Topic: High Performance CAMSHAFT Chain tensioner for CB750(MessnerMoto)

[bwaller]

That was a damn tough race for 60's technology. I can't believe they wouldn't check for coil bind, #$%* they designed and maintained 20K rpm GP bikes, these old 2 valve engines at half that rpm are simple in comparison. 

It was early days for this design. Let's face it "survival of the fittest" comes to mind, DNF's were not uncommon in those days.

[kmb69]

That was a damn tough race for 60's technology. I can't believe they wouldn't check for coil bind, #$%* they designed and maintained 20K rpm GP bikes, these old 2 valve engines at half that rpm are simple in comparison. 

It was early days for this design. Let's face it "survival of the fittest" comes to mind, DNF's were not uncommon in those days.

They made the decision to race at Daytona fairly late in the Summer of '69 and had very little time to make it happen. Pretty incredible what they pulled off!

[bwaller]

+1

[Captain]

 With the passing of time and the engineering  and  knowledge advances since it would be fair to say they were very - very lucky to win (Daytona)
Honda didn’t have any idea of the reasons for the poor cam chain performance as they repeated the same engineering mistakes across the whole range during that era.   The only reason they got away with it was because of the different crank to cam distances and RPM ceilings of various engines.
The greater the distance and higher the RPM the greater the harmonic event.
 To make this easier for some to visualise.......think of the old classic automotive fan belt and how it can act like a guitar string at high RPM. This is exactly what is happening to the cam chain inside these engines at high speed.


 Captain

[MRieck]

That was a damn tough race for 60's technology. I can't believe they wouldn't check for coil bind, #$%* they designed and maintained 20K rpm GP bikes, these old 2 valve engines at half that rpm are simple in comparison. 

It was early days for this design. Let's face it "survival of the fittest" comes to mind, DNF's were not uncommon in those days.

Like no $hit Brent. I thought those fellas were pros?

[MRieck]

so you think all the oil went out the exhaust guides?I can see the idea of some smoke but not that much oil consumption,but I could be wrong.bill

I'd say it went out intake/exhaust guides and past rings. Did those bikes have catch cans? If so i imagine they were stuffed full or the oil blew out the breather tube. I bet the track was a mess after those bikes raced...2 strokes, Harley's and British triples. Oil everywhere. Lucky it is a huge track.

[PeWe]

so you think all the oil went out the exhaust guides?I can see the idea of some smoke but not that much oil consumption,but I could be wrong.bill

I'd say it went out intake/exhaust guides and past rings. Did those bikes have catch cans? If so i imagine they were stuffed full or the oil blew out the breather tube. I bet the track was a mess after those bikes raced...2 strokes, Harley's and British triples. Oil everywhere. Lucky it is a huge track.

They started on a gravel track that turned to asphalt end of the race. The old English bike are less on the roads nowadays so the asphalt need a new recipe since they are way too dry and crack early....

[MessnerMoto]

Thank you guys for all the info... There is a lot to be learned here.

If anyone has any suggestions to make on my design please feel free to do it.

There is still time to make small changes because production of tooling will not start before mid of May.

mirko

[HondaMan]

I'm in for 3 but I am curious about what happens when a cylinder and head have been really decked/milled. I'd imagine the 94 link would work??

I’ve read in an old article about Yoshimura that they would shim up the rocker towers a small amount in an effort to improve cam chain life with whatever adjuster they were using at the time.  Odd solution, but the towers could be shimmed up the same amount as any decking would reduce.

George

This particular "fix" was done for those engines with decked head and cylinder faces, domed-and-clearanced pistons, 811cc size, and the normal rubber tensioners. When run with the 95 HP Yoshimura cam, the chain stretch at 9500+ RPM was so much that it developed too much angle in the chain path, flinging the oil out of the chain at those turns and causing short chain life. Like Mike's idea, a shorter chain was later used, being easier than installing the raised cam bearings.

[gschuld]

Interesting, thanks for sharing Mark🧐

George

[HondaMan]

Interesting, thanks for sharing Mark🧐

George

It's just another one of those things that, along with a $1 bill, can still get a Coke at MacDonalds'.

[kmb69]

.....
This particular "fix" was done for those engines with decked head and cylinder faces, domed-and-clearanced pistons, 811cc size, and the normal rubber tensioners. When run with the 95 HP Yoshimura cam, the chain stretch at 9500+ RPM was so much that it developed too much angle in the chain path, flinging the oil out of the chain at those turns and causing short chain life. Like Mike's idea, a shorter chain was later used, being easier than installing the raised cam bearings.

TOTAL GIBBERISH!     

The heads and cylinders would have to be milled a combined total of 6.35mm or .25" to run a shorter chain unless you're dumb enough to run a half link.

.....
It's just another one of those things that, along with a $1 bill, can still get a Coke at MacDonalds'.

VERY true. 

[eli]

One more, please

[BigJimG]

Definitely interested, in at least one, maybe more depending on my budget at the time...

[HondaMan]

The shorter chains were used: I saw this done myself at Mannheim Honda in 1971. Keep in mind, the pistons were not the ones we see now: they were both rimmed and domed (much like the -392- pistons, but lower shoulders and taller domes) in 811cc size, the cylinders were decked (on those it was 1.00 mm or 0.040") to bring the piston shoulders to the top edge of the [compressed] head gasket when assembled, and the head was decked 0.020" more for a total height loss of 0.75mm (0.060"). When the cam and chain were assembled and the tensioner "set", there was almost no length left on the tensioner's rod, as the lockbolt was sitting against the edge of the notch on the outer end of the shaft. Always the experimenter, their head wrench (Mike) pulled the cam out, broke the chain and removed a full link and riveted it temporarily together (it wasn't run with a riveted chain, not to worry) to test-fit: while it was as snug as a K7 engine with the K4 front tensioner installed, it went back together fine. While I wasn't there when it went racing, I know the pit crew found a 1-link shorter endless chain before the season started, and it ran that way the whole season. I did see the bike in late 1971 when I went to Chicago for Christmas that year, and it had done well in local roadraces.

Honest!

[kmb69]

The shorter chains were used: I saw this done myself at Mannheim Honda in 1971. Keep in mind, the pistons were not the ones we see now: they were both rimmed and domed (much like the -392- pistons, but lower shoulders and taller domes) in 811cc size, the cylinders were decked (on those it was 1.00 mm or 0.040") to bring the piston shoulders to the top edge of the [compressed] head gasket when assembled, and the head was decked 0.020" more for a total height loss of 0.75mm (0.060"). When the cam and chain were assembled and the tensioner "set", there was almost no length left on the tensioner's rod, as the lockbolt was sitting against the edge of the notch on the outer end of the shaft. Always the experimenter, their head wrench (Mike) pulled the cam out, broke the chain and removed a full link and riveted it temporarily together (it wasn't run with a riveted chain, not to worry) to test-fit: while it was as snug as a K7 engine with the K4 front tensioner installed, it went back together fine. While I wasn't there when it went racing, I know the pit crew found a 1-link shorter endless chain before the season started, and it ran that way the whole season. I did see the bike in late 1971 when I went to Chicago for Christmas that year, and it had done well in local roadraces.

Honest!

Dude, you're in Colorado right? I want some of what you've been smoking! The more you try to defend that BS, the fuzzier it gets! 

To remove 1 link, or 1 pitch, requires what's called an offset link. Picture attached. Did you ever wonder why chains usually come in even lengths?
Even if your pal used an offset link, the cylinder and head would have to be decked 3.175mm or .125" combined unless your using plumb stretched out chain!

[MRieck]

You are correct....even #'s only. You have been around this stuff?

[MessnerMoto]

Just to inform general public;) that production has started.

In the end everything is done on CNC. There is no plastic injection tooling etc.

I opted for PA 6.6 + MoS2 plastic.

Also, I will be able to adjust tensioner shoe according to your decking. Maximum is 2mm. But that will cost extra. Nothing expensive but tensioner show needs to go on CNC again....

[slikwilli420]

It would be interesting to test this at high RPM's vs stock system to see how much less the valve timing varied without the chain whipping about. A unit that would dynamically tension the chain would be a nice addition over the stock unit as well.

[MessnerMoto]

Things are getting ready....

Stainless still support plates cut on laser CNC

[MessnerMoto]

Finally plastic started arriving from CNC shop. When you depend on other people things usually get delayed

[slikwilli420]

Awesome. Looking forward to beating the piss out of this on the race bike next year.

[StanLipert]

Mirko,
There is NO modern engine that has so many changes in direction for the cam chain. Overly clever design, but un-tested in racing/stiff valve spring/high lift cam at redline  application. Ken Miller's KA tensioner has been proven to be reliable in dozens of 1/4 mile dirt track racing engines for 20 years, the solution has been around that long.

[MessnerMoto]

Mirko,
There is NO modern engine that has so many changes in direction for the cam chain. Overly clever design, but un-tested in racing/stiff valve spring/high lift cam at redline  application. Ken Miller's KA tensioner has been proven to be reliable in dozens of 1/4 mile dirt track racing engines for 20 years, the solution has been around that long.

This solution is tested with cx-7 cam with 0.4"(10.16mm) lift and Bee-Hive Racing Springs. There was no higher lift cam when I assembled the engine one year ago. Works all over the range without the problem.

This is a copy of modern cam tensioner systems(image provided) used probably since 80". And similar solution already exists for DOHC CB engines, provided by Vince and Hyde Racing from NZ, design by Brent(Captain on this forum)

Nothings is invented here. The trick part was not to invent something but to fit and transfer modern system and materials in to existing cam tunnel of cb750 sohc engine.

Mirko

[StanLipert]

Mirko,
There should be one arc against a supporting slider between each sprocket, if possible. You have a roller changing direction in the front and back runs. How many hours at red line has you engine on it?