Topic: Rocker Tower Bracing

[ealanm]

I'm overhauling a race-prepared CB750 engine that was built by someone else (I know not who).  It has bolts through the rocker cover intended to stiffen the rocker towers.  Does anybody know how these are meant to be used?  Do you just snug them up to the rocker towers and then tighten the jam nuts?  Is there a recommended torque spec?

I'd upload a photo but I can't figure out how.

[MCRider]

I'm overhauling a race-prepared CB750 engine that was built by someone else (I know not who).  It has bolts through the rocker cover intended to stiffen the rocker towers.  Does anybody know how these are meant to be used?  Do you just snug them up to the rocker towers and then tighten the jam nuts?  Is there a recommended torque spec?

I'd upload a photo but I can't figure out how.

The reinforced rocker cover was first used on the original CR750s (I think). Certainly shortly after. RC (Russ Collins), Action 4s, and many others used them. I am using one on my project, many of the racers here use them. They are mostly now made as one offs by various machinists, though some like 3M Racing have them in catalogs.

Current school of thought is that they may not be necessary as the current crop of heavy duty springs and cams are not so hostile to the rocker stands, not trying to distort them and tear them from their roots. It gives me some peace of mind however as I had some problems in this area years ago and why not? They look cool.

To your actual question, we had a thread on it recently and the consensus I came away with is that little presure is needed for them to do their job. Something like 5lbs torque and a good snug on the lock nuts will do it.

I'd certainly entertain any engine builder wanting to revisit this issue.

[kos]

Yes, these were first shown on the cover of the Cycle magazine Oct 1970 where all the parts were lay-ed out on the cover with the Dick Mann bike in the background. Funny thing is, there never was a part number in the CR parts list for this cover and none of the factory bikes ever used the cover with the 6mm hold down screws! In all of my CR750 parts hunting over the last 40 years I have never found real Honda made cover like the one shown on that cover of cycle magazine.  As far as pressure, we recommend that once you have the cover bolted to the top of engine, that you then just screw down the bolt/screw until it touches the cam tower, then tighten the nut .

KOS

[MCRider]

Yes, these were first shown on the cover of the Cycle magazine Oct 1970 where all the parts were lay-ed out on the cover with the Dick Mann bike in the background. Funny thing is, there never was a part number in the CR parts list for this cover and none of the factory bikes ever used the cover with the 6mm hold down screws! In all of my CR750 parts hunting over the last 40 years I have never found real Honda made cover like the one shown on that cover of cycle magazine.  As far as pressure, we recommend that once you have the cover bolted to the top of engine, that you then just screw down the bolt/screw until it touches the cam tower, then tighten the nut .

KOS

Thanks for the backstory, isn't that weird. I could've sworn i saw a picture of a CR750 with the cover, but it may have been a misguided repro. If you haven't found it, I'm guessing it doesn't exist ... in the CR world that is.

Thanks for the confirm on bolt pressure.

[ealanm]

Thanks guys, that info on bolt pre-load makes sense.  On mine, you can clearly see where the tips of the bolts have been in contact with the rocker towers, which suggests either that they were done up fairly tight at least once or, possibly, that the flexing of the rocker towers pushes them into the bolts.  I don't think there's anything modern about the cam and springs in my engine, so the bolts are probably necessary, for me.

[rklystron]

Make sure the 6mm bolts are nice and smooth at the bottom where they contact the cam towers. No sharp ends. If you have to take a bit of time and clean them up. It will be worth your while.

[voxonda]

Actually Honda did use these cover bolts. Have a picture of a Sumiya/Hishiki bike with this setup. Will see if I can scan it tonight and place it here.

Rob

[lordmoonpie]

Actually Honda did use these cover bolts. Have a picture of a Sumiya/Nishiki bike with this setup. Will see if I can scan it tonight and place it here.

Rob

Rob - do you mean the '69 Hisiki/Sumiya bike or the later blue/red Sumiya bike? If it's the early one that picture sure would be appreciated, I've only ever seen sketches of it or B&W photos without fairings and tank, never the full thing...

[voxonda]

It is neither one of these bikes, but one they seem to have used during the 8 hour of Suzuka. Tonight will scan that pic. You can clearly see the cover and the hold down bolts.

rob

[voxonda]

Hey LMP,

This is the picture:

Is from "Honda Motorcycle Racing Legend vol.3"

[lordmoonpie]

Nice pics thanks Rob - I guess the whole book is in Japanese is it?

[voxonda]

Yes, is in Japanese. Did you get a look at that valve cover?

Rob

[nippon]

Nice pics!
Did they just remove the vertical bars between the cylinder head fins in the pic at the bottom or what type of cylinder head is this? Any close ups available?

[voxonda]

Nice pics!
Did they just remove the vertical bars between the cylinder head fins in the pic at the bottom or what type of cylinder head is this? Any close ups available?

These heads are milled down to the width of the cylinder block, so the fairing could be narrower. As you look closely you'll see the cooliing fins are straight(er) than the standard heads.

[nippon]

got it, thanks.

[daley]

Is this what your valve cover looks like?

[kos]

Hey LMP,

This is the picture:

Is from "Honda Motorcycle Racing Legend vol.3"

That is not a factory bike pictured and that top cover is just something a local tuner did during the period. There was never a CR kit cover and non of the "works" Honda RC750's ever used them.

Bike in picture appears to have a street oil tank and standard EOM street bike carbs, nothing Honda factory would run.

I know Mike H personally and he did a lot of , afterwork projects while at Honda in Japan and in California at AHM (American Honda Motor Co, Inc)

In fact, the chassis that is the basis of the CR kit bike I have in Barber Museum was something Mike did while he worked for a dealer in Pennsylvania, USA. It was an awful looking thing, worse than  a Pops Yoshimra preped bike of the era. But is did compete at Daytona 1971.

KOS

[MCRider]

I accept i was wrong about the cover being used on CRs. I had qualified my statement with "I think". Likely the first production units were made by RC as he had them in his catalog. Although I can't say for sure i ever saw an RC cover, other than in pictures of RC Cobra motors. 

Many before during and since were hand made one or two offs by various machinists. Hence they all have different looks to them. Some use square lugs, some round, some use 8mm bolts, some 6mm, some are allens, some are hexheads, etc.

The one I have now was made by Les Barker somewhere in the Pacifc NW. He claimed to have gotten the pattern from someone selling patterns that RC had sold.

RC used higher lift cams than the roadracers (again, I think) and thus the extra hold down strength was necessary. With the wimpy cam I'm going to use, i fully agree the reinforced cover is over kill. But I think it looks SOooooo kewl!   

[paulages]

I accept i was wrong about the cover being used on CRs. I had qualified my statement with "I think". Likely the first production units were made by RC as he had them in his catalog. Although I can't say for sure i ever saw an RC cover, other than in pictures of RC Cobra motors. 

Many before during and since were hand made one or two offs by various machinists. Hence they all have different looks to them. Some use square lugs, some round, some use 8mm bolts, some 6mm, some are allens, some are hexheads, etc.

The one I have now was made by Les Barker somewhere in the Pacifc NW. He claimed to have gotten the pattern from someone selling patterns that RC had sold.

RC used higher lift cams than the roadracers (again, I think) and thus the extra hold down strength was necessary. With the wimpy cam I'm going to use, i fully agree the reinforced cover is over kill. But I think it looks SOooooo kewl!   

Les is still here in Portland, Oregon (well, across the river in Vancouver, WA). I have a CB550 race bike he built in the late '70's. You can find him at his site: http://www.vintageadvantagemotorcycles.com/

[MCRider]

I accept i was wrong about the cover being used on CRs. I had qualified my statement with "I think". Likely the first production units were made by RC as he had them in his catalog. Although I can't say for sure i ever saw an RC cover, other than in pictures of RC Cobra motors. 

Many before during and since were hand made one or two offs by various machinists. Hence they all have different looks to them. Some use square lugs, some round, some use 8mm bolts, some 6mm, some are allens, some are hexheads, etc.

The one I have now was made by Les Barker somewhere in the Pacifc NW. He claimed to have gotten the pattern from someone selling patterns that RC had sold.

RC used higher lift cams than the roadracers (again, I think) and thus the extra hold down strength was necessary. With the wimpy cam I'm going to use, i fully agree the reinforced cover is over kill. But I think it looks SOooooo kewl!   

Les is still here in Portland, Oregon (well, across the river in Vancouver, WA). I have a CB550 race bike he built in the late '70's. You can find him at his site: http://www.vintageadvantagemotorcycles.com/

Not to hijack the thread, but OK its hijacked. Mentioning Les made me look him up and I found his site. I think I originally found him thru the Vintage Japanese Motorcycle Club when I needed to have the cam chain tensioner on my 305 SuperHawk repaired. He fitted it with a new wheel and needle bearing of his design. Nice work. OEM stuff no longer available. I mentioned my project and he said he could make the cam cover, and did. That was nearly 12 years ago. If I ever get it finished I'll send him a picture.  Hope he's doing well.

[voxonda]

Hey LMP,

This is the picture:
Is from "Honda Motorcycle Racing Legend vol.3"

That is not a factory bike pictured and that top cover is just something a local tuner did during the period. There was never a CR kit cover and non of the "works" Honda RC750's ever used them.

Bike in picture appears to have a street oil tank and standard EOM street bike carbs, nothing Honda factory would run.

I know Mike H personally and he did a lot of , afterwork projects while at Honda in Japan and in California at AHM (American Honda Motor Co, Inc)

In fact, the chassis that is the basis of the CR kit bike I have in Barber Museum was something Mike did while he worked for a dealer in Pennsylvania, USA. It was an awful looking thing, worse than  a Pops Yoshimra preped bike of the era. But is did compete at Daytona 1971.

KOS

Not to question your knowledge Mark, but it is a picture from a official Honda book. Think maybe there is more under the sun than meets the eye.................................. But does not matter, think it is before RC did it. Pic is from 1970.

Rob

[kos]

RC Engineering was right across the Street from AHM (American Honda Motor Co, Inc) and Russ saw the same cover picture of the DaytonaRC750 and parts on it, as we all did in Oct of 1970, that cover shows what appears to be a top engine cover with welded on cam tower supports and he (Rc Eng) took off and ran with it, as we say over here in the states. And started making his own. This was in 1970 when he offered them.

IMHO, that picture you have posted with that cover, does not appear to be of any high quality that Honda RSC would claim credit for.

Standard carbs and side oil tank with half fairing also fits no known CR I have ever viewed or read about?

I would offer that this is a privately raced entered machine that was helped with addition of RSC parts, save for that cam cover.

We will have to agree, to disagree about this issue.

BTW, we make these covers on CNC machine with hold down bolts that are dead on, within .001" accuracy. And that can also be used as locating points for top engine to frame mounting system we invented. really the only good use for this period modification as with a max of 85 lbs for spring rate, no need for them.

KOS

[voxonda]

No worries Mark, no right or wrong here IMO. Just nice to see the old pic's with parts we still want to have after 40 years.

Cheers, Rob

[Sam Green Racing]

Sorry Mark but the Bike in question IS a factory CR750.
It was entered in an international long distance endurance race in the production class.
The clue is in the two names on the tank, factory development riders Morio and Tetsuya.
The stock oil tank was to make way for the battery and stuff needed to run lights plus spot lights and starter. (check out the Bol-D-Or winning bike)
The stock carbs were to comply with FIM regulations of that period.
Sorry Mark, Rob wins this time.

Sam.

[kos]

Last I heard, Mike H is still with us so I will contact him and get his take on this debate and then we can put a period on this!


KOS