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Motorcycle Flat Track Racing

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Aug 15, 2020 - 10:05:55 AM
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5317 posts since 9/16/2004

Here's a bit of history for the motorheads among us.

Two historical racing bikes.  Always looking for a competitive edge, these professional race bikes were fitted with Moto One Road Racing engines.  Capable of straight-a-way speeds in excess of 140 MPH on one mile horse tracks, they raised the risk of injury too high.  Both were outlawed in 1975. 

Aug 15, 2020 - 10:29:43 AM

3506 posts since 7/8/2010

Fred, I sure miss mc events that I attended in so cal in the seventies. Notably: Superbowl of Motocross at the LA Coloseum, the races at Ontario Motospeedway and the flat track races at Irwindale.
The one-fifth flat track races were the most exciting. Some of you will remember Billy Gray from Father Knows Best. He was Bud Anderson in the series. What a competitor he was.

Aug 15, 2020 - 11:31:27 AM

10678 posts since 1/15/2005

John ..... my flat track career consisted on a very short (probably a 1/10th mile track) called Glassy Mountain Raceway up near Landrum, SC. We used to get some really good riders there, but I was not one of them. I was racing an OSSA (250 CC Mick Andrews model) that was meant to "trials" riding, so I was at a huge disadvantage. My racing boot on my left foot consisted of an old Marine Corps combat boot with the heel removed. I made the finals heat once when two Harley's both popped their front ends up at the start and could never recover. Lots of fun!

Aug 15, 2020 - 11:58:17 AM

397 posts since 1/28/2011

The picture on the left looks like Ray Abrams with the Kenny Roberts Yamaha TZ750. Ray owned A&A racing and was a major parts supplier for many of the dirt track racers in the 70's and 80's. and also sponsored many of them. Kenny Roberts rode that thing a couple of times, but the engine had so much horsepower that it caused the tire tread to flex so much that the bike would go into a ferocious wobble on the straightaway. The road race bikes that the engine was designed for had slick tires that would not flex, but the slicks would not work in the corners on a dirt track. It was an impossible situation without a complete redesign of dirt track tires. Kenny said that it was too dangerous as it was, and the AMA agreed and banned it. I watched it on two race tracks, San Jose Mile, and Indianapolis Mile. It was scary just to watch it and any rider less talented than Kenny would probably have wrecked.

Aug 15, 2020 - 12:28:13 PM

5420 posts since 12/20/2005

Long time ago I read Dick Mann's biography, or autobiography, I don't recall which. Probably in 1975.
I was in high school. Nuts about motorcycles.
My dad had a BMW R90S. It was modified a bit and would run away from a Kawasaki 900.
My parents forbid that I could have one. Like I wanted. Would have been a Honda CB 750. I have to be grateful for that now. I would have been dead within a week.
But they did get us kids a Hodaka Combat Wombat. Loudest motorcycle I ever heard. It had this huge chrome gas tank and terrible suspension. We had it a while and it was a blast, but we tore it up.
I never got to see a flat track race. I have not thought about it in so long. I'll have to check out what might be on YouTube.

Aug 15, 2020 - 12:51:15 PM

DRH

USA

535 posts since 5/29/2018

That Yamaha appears to be built around the TZ engine. The Kawasaki is a Mach 3 variant. Both engines were squirrelly, even on pavement. A stock, street legal Mach 3 was the most frightening bike I've ever been on. It handled like a shopping cart. The TZ was designed and available only for pro class road racing. The sound alone would make you pee your pants if you were standing too close to the rail.

But the AMA ban was political and had nothing (other than the excuse) to do with safety. Harley Davidson's XR750 was the only American motorcycle left and it was underpowered on the mile tracks. The AMA Nationals were being taken over by Japanese bikes. At that time AMA meant AMERICAN MOTORCYCLE Association and the executive board was not apologetic about it.

Aug 15, 2020 - 1:38:57 PM

DRH

USA

535 posts since 5/29/2018

quote:
Originally posted by latigo1

The picture on the left looks like Ray Abrams with the Kenny Roberts Yamaha TZ750.


If that was Kenny's TZ750 then it was a road racer with different wheels and the fairings removed.  AMA rules at that time only allowed production bikes (200+ units) in the Nationals.   The TZ750 was barely controllable on blacktop and would have been insufferable on dirt, particularly with a road frame and tuning.

Aug 15, 2020 - 1:40:39 PM

heavy5

USA

1308 posts since 11/3/2016

I began to appreciate 2 strokes when cart racing in the 60's souping up mostly McCullough motors . Then fast forward many motorhead years w/ 2 stroke bikes & into building & flying ultralights w/ Rotax motors which I became very familiar with .
This established my belief in some 2 strokes as being the lightest highest horse power plants for some applications .
My story & I'm sticken w/ it .

Aug 15, 2020 - 3:20:12 PM
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397 posts since 1/28/2011

quote:
Originally posted by DRH
quote:
Originally posted by latigo1

The picture on the left looks like Ray Abrams with the Kenny Roberts Yamaha TZ750.


If that was Kenny's TZ750 then it was a road racer with different wheels and the fairings removed.  AMA rules at that time only allowed production bikes (200+ units) in the Nationals.   The TZ750 was barely controllable on blacktop and would have been insufferable on dirt, particularly with a road frame and tuning.

 


The AMA  rules only applied to engines, not frames or complete bikes.  That engine was from a Yamaha TZ750 road racer and there were over 200 available at the time, and AMA rules did not specify it be used in any one particular type race.  It was OK by AMA rules to be used in dirt track races.  That bike had a custom built Schwerma "Champion"  frame built strictly for that bike for dirt track racing.  A road race frame would not be anywhere close to what was necessary for dirt track racing.  At the time, even Harley offered thier 750 dirt track motor for sale and people were using several different frames to build dirt track racers. The three primary frames used were Trackmaster, Red Line, and Champion.  Most, if not all, dirt track bikes were built up units, and if it had an AMA approved engine it could be one of a kind.  Most people bought an engine from whatever company they wanted. Harley was the most common flat track engine, but there were still some Triumph's, BSA's, and the Ron Wood Norton running.  Many other brands were used for short track and TT.  Then you bought the fiberglass seat and tanks from one place, (usually from John Silberbauer in San Jose), the brakes and wheels, and forks from another (usually from Sandy Kosman or Barnes).  Handlebars, levers,  throttles, shocks, and other small parts from your local dealer, and put it all together in your garage.

Aug 15, 2020 - 3:41:59 PM
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RonR

USA

1683 posts since 11/29/2012

I pulled my 42 flathead Trog racer out today. After 20 kicks and several shots of ether it actually ran. It has been sitting too long. A few times around the block and I was happy.


 

Aug 15, 2020 - 3:52:58 PM

10678 posts since 1/15/2005

Cool looking bike Ron. My '69 Triumph Bonneville is still sitting in the corner of my garage still gathering dust after I put it up almost 30 years ago. My children were young and I was in the prime of my earning years, when I was out in the large field in front of my house trying to get the second carburetor to kick in (after the bike had sat for several months). The grass was damp and I was in a slight turn accelerating when the second carb kicked in. The rear wheel started spinning and I just laid the bike down injuring the knee on one leg and the hamstring on the other. I was able to get up pick up the bike and wheel it to the garage where it has been ever since.

Aug 15, 2020 - 3:59 PM

DRH

USA

535 posts since 5/29/2018

I thought the 200+ production requirement applied to the frame and engine. I stand corrected.

Aug 15, 2020 - 4:03:12 PM

RonR

USA

1683 posts since 11/29/2012

I always liked the antique machines. I certainly am not a racer at 66 years old. 26 horsepower suits me fine.

Aug 15, 2020 - 4:05:58 PM
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5317 posts since 9/16/2004

quote:
Originally posted by RonR

I pulled my 42 flathead Trog racer out today. After 20 kicks and several shots of ether it actually ran. It has been sitting too long. A few times around the block and I was happy.


the picture is muli time National Champion Carroll Resweber on a factory racer version of your rigid flathead Harley.  This bike was competitive into the late 60's


 

Aug 16, 2020 - 8:35:50 AM

5317 posts since 9/16/2004

The two race bikes in the opening post are a Yamaha TZ750 and a 750 HR2 Kawasaki. Both bikes have historical significance. The number 19 Kawasaki on the right is/was owned by World Champion tuner Irv Kanemoto and was ridden by National Champion, Gary Nixon and later by Scott Brelsford. The TZ750 Yamaha powered race bike was built by the Yamaha team of World Champion Kel Carruthers and World Champion Kenny Roberts in response to the dominating speed of the Kawasaki ridden by Brelsford. It was Brelsford who first demonstrated the potential of powering Flat Trackers with Moto One engines.

Scott Breslford, along with Champion Frames, Doug Schwarma were responsible for figuring out the necessary chassis changes to make the road race engine's power delivery work on a dirt oval. Brelsford's air cooled Kawasaki was the first to win an AMA (non-National) Mile Race at Stockton California. Immediately after, the Yamaha team were working with Champion Frames to fit their water cooled Road Race engine into the recently developed chassis. Yamaha powered bikes ended up dominating the Mile tracks. Brelsford's faster Kawasaki never overcame the overheating problems associated with air cooling. The slower but cooler running Yamaha outlasted the air cooled Kawasaki. Oddly, it was the Yamaha that got the credit for developing this engine and chassis combination. Proving once again that history is indeed written by the winner.

Everything in professional motorcycle racing was changing in the decade of the seventies. In last half of 1974, the American Motorcycle Association (AMA) changed the decades old homologation rule requirements necessary for a motorcycle's eligibility to compete in professional competition. It was done surreptitiously to accommodate Harley Davidson's entry into the Road Race portion of National Championship series. The rule change was to reduce the 200 complete motorcycle requirement down to just 25 engines. Now, all a factory had to do was make 25 engines available to be legal to compete. By the last half of the decade, the Road Race powered bikes were outlawed for competition. The claim was, they were too fast and way too dangerous (see photo.) Road Racing was no longer part of the AMA National Championship Series. Road Racing was divided into multiple classes with their own multiple championships... The halcyon years of "On Any Sunday" motorcycle racing was over.


Aug 16, 2020 - 9:53:27 AM

397 posts since 1/28/2011

John, I agree with most of what you say, except about Yamaha dominating the mile tracks. Yamaha was never successful on mile tracks. There were a few riders using the XS650 twin, including Kenny Roberts who was their factory rider. That engine was never successful on mile tracks. When they finally got enough horsepower and flywheel weight to be competitive on mile tracks the reliability suffered, with broken crank cases being a major problem. When they built the TZ 750 it was only run a few times, and won only one race. Shortly after, Kenny went off to Europe to compete in world class road racing and Yamaha in America lost interest in flat track racing until they came out with the V twin Virago. The 25 engine homologation rule allowed Yamaha to build 25 Virago engines with chain drive instead of the standard drive shaft street version, which would not have worked for a dirt tracker. Yamaha had their factory team of Mike Kidd and Jimmy Felice, using CR Axtell to build their engine and using, if I remember correctly, Red Line frames. They also had a support team in northern California with rider Billy Scott, and frames by Terry Knight and I built the engines. It didn't take long to realize the Virago engines had traction problems on dirt tracks. I felt the problem was caused by the Virago engine rotating counter clockwise instead of the more common clockwise rotation of the Harley engine. Yamaha didn't agree, and even though I cobbled together a clockwise engine, and tested it with promising results, Yamaha decided to disband the Virago project and concentrate on road racing and moto cross. All history now, but it was fun (and a lot of work) while it lasted. Interesting to run across someone with your interest and knowledge of dirt track racing on a banjo forum.

Aug 16, 2020 - 10:50:41 AM

10678 posts since 1/15/2005

Great post Dave & John! I think there are a number of us on the HO that like racing and grew up with it, but there are very few with you guys inside knowledge on any forum, except maybe a motorcycle forum. I grew up when the Honda Scrambler had just came on the market and that is when many of us were introduced to dirt track racing. Of course it had been going on for years, particularly flat track racing, but it wasn't until them that most people could go to a bike shop and buy one of the showroom floor and have it at a motocross/scramble track the next day. That was also about the time (maybe 10 years early or so) when the Japanese bikes started overtaking the European (mostly English) bikes. A buddy of mine and I went to Europe in 1972 and our first stop was in London to buy English bikes. It was then that we noticed that all of the other serious European riders were on Japanese bikes. The British companies trying to keep pace with the Japanese bikes was pretty much a failure (i.e Triumph Trident). I guess there is only so far you can go with a Lucas electrical system!

Aug 16, 2020 - 11:39:44 AM

397 posts since 1/28/2011

quote:
Originally posted by BanjoLink

Great post Dave & John! I think there are a number of us on the HO that like racing and grew up with it, but there are very few with you guys inside knowledge on any forum, except maybe a motorcycle forum. I grew up when the Honda Scrambler had just came on the market and that is when many of us were introduced to dirt track racing. Of course it had been going on for years, particularly flat track racing, but it wasn't until them that most people could go to a bike shop and buy one of the showroom floor and have it at a motocross/scramble track the next day. That was also about the time (maybe 10 years early or so) when the Japanese bikes started overtaking the European (mostly English) bikes. A buddy of mine and I went to Europe in 1972 and our first stop was in London to buy English bikes. It was then that we noticed that all of the other serious European riders were on Japanese bikes. The British companies trying to keep pace with the Japanese bikes was pretty much a failure (i.e Triumph Trident). I guess there is only so far you can go with a Lucas electrical system!


Oh yes!  Joseph Lucas, better known as the Prince of Darkness.  Owner of the Lucas Electric Co, and inventor of the three position headlight switch:  Off, Dim, and Flicker.  Great stuff, as long as you got home before dark.  On the other hand, a great contributor to the lack of auto thefts in England.  The thiefs could never figure out exactly how to wiggle the key to make the ignition switch to turn on.

Aug 16, 2020 - 11:46:20 AM

10678 posts since 1/15/2005

quote:
Originally posted by latigo1
quote:
Originally posted by BanjoLink

Great post Dave & John! I think there are a number of us on the HO that like racing and grew up with it, but there are very few with you guys inside knowledge on any forum, except maybe a motorcycle forum. I grew up when the Honda Scrambler had just came on the market and that is when many of us were introduced to dirt track racing. Of course it had been going on for years, particularly flat track racing, but it wasn't until them that most people could go to a bike shop and buy one of the showroom floor and have it at a motocross/scramble track the next day. That was also about the time (maybe 10 years early or so) when the Japanese bikes started overtaking the European (mostly English) bikes. A buddy of mine and I went to Europe in 1972 and our first stop was in London to buy English bikes. It was then that we noticed that all of the other serious European riders were on Japanese bikes. The British companies trying to keep pace with the Japanese bikes was pretty much a failure (i.e Triumph Trident). I guess there is only so far you can go with a Lucas electrical system!


Oh yes!  Joseph Lucas, better known as the Prince of Darkness.  Owner of the Lucas Electric Co, and inventor of the three position headlight switch:  Off, Dim, and Flicker.  Great stuff, as long as you got home before dark.  On the other hand, a great contributor to the lack of auto thefts in England.  The thiefs could never figure out exactly how to wiggle the key to make the ignition switch to turn on.


LOL Dave ..... so true!

I had a 650 Matchless scrambler that I used for all my transportation my junior year in college.  After a few months the clutch cable broke right at the fork in the housing.  I did not have $15 for a new one so I got one of architecture professors, who was also a sculptor, to try and weld a bead on the end of the cable.  The cable was too brittle so every time he heated it yp the cable wires just crumbled.  Therefore, I drove my bike for three months with no clutch.  The biggest challenge was uphill stop signs which I tried to avoid.  It worked!

Aug 16, 2020 - 1:10:19 PM

DRH

USA

535 posts since 5/29/2018

quote:
Originally posted by latigo1

John, I agree with most of what you say, except about Yamaha dominating the mile tracks. Yamaha was never successful on mile tracks. There were a few riders using the XS650 twin, including Kenny Roberts who was their factory rider. That engine was never successful on mile tracks. When they finally got enough horsepower and flywheel weight to be competitive on mile tracks the reliability suffered, with broken crank cases being a major problem. When they built the TZ 750 it was only run a few times, and won only one race. Shortly after, Kenny went off to Europe to compete in world class road racing and Yamaha in America lost interest in flat track racing until they came out with the V twin Virago. The 25 engine homologation rule allowed Yamaha to build 25 Virago engines with chain drive instead of the standard drive shaft street version, which would not have worked for a dirt tracker. Yamaha had their factory team of Mike Kidd and Jimmy Felice, using CR Axtell to build their engine and using, if I remember correctly, Red Line frames. They also had a support team in northern California with rider Billy Scott, and frames by Terry Knight and I built the engines. It didn't take long to realize the Virago engines had traction problems on dirt tracks. I felt the problem was caused by the Virago engine rotating counter clockwise instead of the more common clockwise rotation of the Harley engine. Yamaha didn't agree, and even though I cobbled together a clockwise engine, and tested it with promising results, Yamaha decided to disband the Virago project and concentrate on road racing and moto cross. All history now, but it was fun (and a lot of work) while it lasted. Interesting to run across someone with your interest and knowledge of dirt track racing on a banjo forum.


The history lessons are much appreciated.  ( And a big thanks to Fred for starting the thread ).  My early interest was flat track racing.  By the time I could afford to race everybody was into motocross.  I cut my own short track and spent many hours on it.

I followed the great AMA riders of the 60's and 70's but eventually succumbed to motocross.  By 1976 amateur riders were deliberately running over downed riders.  A friend saw five riders run over me in practice - I was unconscious.  So I turned to desert racing.

By the time short track got popular in Oregon again I was living on the wrong side of the state and trying to feed a family.

I recall reading somewhere that Harley Davidson's advantage on flat tracks was due to the crankshaft configuration.  The pulsing nature of the engine allowed better feel and control of wheel spin.  The inline (2 and 4 stroke) Japanese engines were all squirrelly to me. 

When the Japanese V twins came out I expected them to take over flat track.  They never did as far as I know.  The light flywheel and double throw crankshaft may have been what made them less controllable on dirt.  But at least they didn't shake.  Honda eventually built a single throw crankshaft V twin, hoping the shaking and "potato sound" would appeal to ex-Harley riders.  I don't know if it went into production.  It probably would have made a good circle burner.

Yamaha's XS650 might have been competitive but for many design flaws.  I think it was the worst engine Yamaha ever built.  The Yamaha dealer I worked for wouldn't even stock them.  I don't recall much about the TZ750 miler but I understand now why Roberts tried it.  I remember him being frustrated with the XS650.

Aug 16, 2020 - 2:49:13 PM
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397 posts since 1/28/2011

quote:
Originally posted by DRH
quote:
Originally posted by latigo1

John, I agree with most of what you say, except about Yamaha dominating the mile tracks. Yamaha was never successful on mile tracks. There were a few riders using the XS650 twin, including Kenny Roberts who was their factory rider. That engine was never successful on mile tracks. When they finally got enough horsepower and flywheel weight to be competitive on mile tracks the reliability suffered, with broken crank cases being a major problem. When they built the TZ 750 it was only run a few times, and won only one race. Shortly after, Kenny went off to Europe to compete in world class road racing and Yamaha in America lost interest in flat track racing until they came out with the V twin Virago. The 25 engine homologation rule allowed Yamaha to build 25 Virago engines with chain drive instead of the standard drive shaft street version, which would not have worked for a dirt tracker. Yamaha had their factory team of Mike Kidd and Jimmy Felice, using CR Axtell to build their engine and using, if I remember correctly, Red Line frames. They also had a support team in northern California with rider Billy Scott, and frames by Terry Knight and I built the engines. It didn't take long to realize the Virago engines had traction problems on dirt tracks. I felt the problem was caused by the Virago engine rotating counter clockwise instead of the more common clockwise rotation of the Harley engine. Yamaha didn't agree, and even though I cobbled together a clockwise engine, and tested it with promising results, Yamaha decided to disband the Virago project and concentrate on road racing and moto cross. All history now, but it was fun (and a lot of work) while it lasted. Interesting to run across someone with your interest and knowledge of dirt track racing on a banjo forum.


The history lessons are much appreciated.  ( And a big thanks to Fred for starting the thread ).  My early interest was flat track racing.  By the time I could afford to race everybody was into motocross.  I cut my own short track and spent many hours on it.

I followed the great AMA riders of the 60's and 70's but eventually succumbed to motocross.  By 1976 amateur riders were deliberately running over downed riders.  A friend saw five riders run over me in practice - I was unconscious.  So I turned to desert racing.

By the time short track got popular in Oregon again I was living on the wrong side of the state and trying to feed a family.

I recall reading somewhere that Harley Davidson's advantage on flat tracks was due to the crankshaft configuration.  The pulsing nature of the engine allowed better feel and control of wheel spin.  The inline (2 and 4 stroke) Japanese engines were all squirrelly to me. 

When the Japanese V twins came out I expected them to take over flat track.  They never did as far as I know.  The light flywheel and double throw crankshaft may have been what made them less controllable on dirt.  But at least they didn't shake.  Honda eventually built a single throw crankshaft V twin, hoping the shaking and "potato sound" would appeal to ex-Harley riders.  I don't know if it went into production.  It probably would have made a good circle burner.

Yamaha's XS650 might have been competitive but for many design flaws.  I think it was the worst engine Yamaha ever built.  The Yamaha dealer I worked for wouldn't even stock them.  I don't recall much about the TZ750 miler but I understand now why Roberts tried it.  I remember him being frustrated with the XS650.


The Harley crankshaft was exactly why they were successful on those hard, slick, mile tracks.  They ran both cylinders off of one crank pin, which meant that there was an uneven firing sequence between the front and back cylinders.  That is why Harley's sound the way they do.  The HD crankshaft is also heavy and a large diameter.  The rotating weight helps them hook up and prevents the engine from revving up so fast that it breaks the rear wheel loose.  The down side was, it was a dry sump oil system and if any oil collected in the crankcase, the flywheels would pull it up between the crankcase and flywheel and cause a hydraulic drag that would pull about 15 horsepower out of the motor.   As far as the Japanese V twins go, Yamaha was not successful for the reasons In my other post, but Honda starting to show an interest in flat track.  Gene Romero was retiring from racing about that time, and Honda bought his Harley from him and sent it to Japan.  That bike was checked and tested by every means available to a large engineering company like Honda.  They measured every dimension on that bike.  When they were done, they knew how much wheelspin was acceptable.  They knew how the swing arm should react, even though they went from a two shock design to a single shock chassis. They knew exact weights and center of gravity, steering head offset, rake and trail, and everything else pertaining to a dirt track race bike.  Then they built three complete bikes and as per AMA rules, made available to the public another 25 of the air cooled V twin engines based on thier water cooled street V twin.  It was called the RS750.  These were crude looking sand cast engines, but they were straight out of  Honda Racing in Japan, and inside they had all the right stuff,  They had 4 valve heads with titanium valves, and bronze valve seats.  The crank was a two throw crank but was timed so it had a firing order closer to a HD.  The flywheels were not as large as a Harley, but had been drilled and heavy Mallory Metal plugs installed to add flywheel weight.  Every thing about that engine was for race only.   I was fortunate to have been on the original R&D team the first year that bike was used.  We spent most of the year shaking out the bugs but before years end Hank Scott rode one to a victory at the Du Quoin mile.  The next several years Team Honda went on to dominate mile track racing with riders Ricky Graham and Bubba Shobert.  Eventually Honda decided to concentrate their racing efforts on Road Racing and Moto Cross, and they disbanded their dirt track team.

  

Edited by - latigo1 on 08/16/2020 14:57:39

Aug 16, 2020 - 3:18:31 PM

5317 posts since 9/16/2004

Thanks Latigo 1,
You've educated me.

Aug 16, 2020 - 3:32:41 PM

397 posts since 1/28/2011

Thanks John, for starting the thread. Dirt track racing was a big part of my life for over 30 years and it brought back a lot of memories.

Aug 17, 2020 - 8:34:01 AM

5317 posts since 9/16/2004

quote:
Originally posted by latigo1

Thanks John, for starting the thread. Dirt track racing was a big part of my life for over 30 years and it brought back a lot of memories.


After reading your comments about Yamaha's Flat Track racing attempt with their XS 650, I began searching my memory for what I remembered.  What I remember confirms what you said about their inherent weaknesses.  I remember seeing one of the Yamaha factory entries with massive welds all around the cases.  If I remember right, when they increased the engine size to 750cc, they began pulling the cylinder studs out of the cases.  Nearly half a century has past since those days.  Is this what you remember? 

    

Aug 17, 2020 - 12:13:55 PM

397 posts since 1/28/2011

quote:
Originally posted by Frisco Fred
quote:
Originally posted by latigo1

Thanks John, for starting the thread. Dirt track racing was a big part of my life for over 30 years and it brought back a lot of memories.


After reading your comments about Yamaha's Flat Track racing attempt with their XS 650, I began searching my memory for what I remembered.  What I remember confirms what you said about their inherent weaknesses.  I remember seeing one of the Yamaha factory entries with massive welds all around the cases.  If I remember right, when they increased the engine size to 750cc, they began pulling the cylinder studs out of the cases.  Nearly half a century has past since those days.  Is this what you remember? 

    


Yes, that is what I remember also.  The cylinder studs were a weak point.  If I remember right, the flanges the studs went through on the cylinders would also break off.  The cases would also break around the main bearings, and some of that welding you mention was to reinforce the cases.  That old engine was fine for a 650cc 40 horsepower street bike, but just didn't have the strength to handle the extra stress of a 750cc 80 horsepower race engine.

                                                 

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