Topic: 78 CB750F3 R2 Cam & rebuild

[garyS-NJ]

I had some sort of top end failure where a loose nut got under my #3/4 rocker holder and busted things up.  rockers, holder, & cam wiped.  and one rocker hold down stripped out the head.  So I had a basket 78 F3 motor in my cellar and grabbed the cam from that (already out of the motor).  My wiped cam is stamped R2 and this basket cam is stamped R1.  I'd like to have the same cam back in the bike (I think) but would also like to know what I have in my hands.  Supposedly the seller took a worked on 1978CB750F motor apart and this is the cam he found.  The basket engine has VIN that shows its a '78 but who knows about the cam (and he also gave me some K model parts).  I did a quick/dirty comparison and the cams look about the same but I'll measure the lob heights (only the bearing (bushing) surfaces of my cam got totaled). I can't measure the degrees.  I poked around to find the markings for my stock cam and what this cam is from but I didn't find much except this thread  http://forums.sohc4.net/index.php?topic=62266.0  which didn't nail it for me (there was different opinions expressed) so I'm hoping a new set of eyes might help.

So my motor before (as much as I know) was stock with the airbox and the stock 4 into 1 pipe.  I knocked the baffle out of the pipe and it ran good.  I ran the points for a year or so and then put in a dyna S when I had to do points again.  I bought an aftermarket copy of K&N pods along with the next size up main jets and I'm only getting to that now.

one guy in above thread says the R1 cam came from a 1969 K motor and was the hottest highest reving cam but I thought the 1978 supersport actually sported a hotter cam than previous years and the '78 K model (that's what made the F model super).  Anyway this R1 came looks pretty good except the bearing surface is a little blued (but not gaulled) on the back side of two lobes.  So bottom line I'd like to put the "right cam in (I could buy a new cam if that's best) for the open header and pods but not build it too lopey/racey.

Inputs on the cam ?? and any other recommendations on motor work to do while the engine is out?

[Don R]

The R number is just a casting number, You need to measure the bump on the cam. There are many threads on the subject.

[Jerry Rxman Griffin aka MuthaF'er]

Unless you are THE original owner there is no way to DEFINITELY know what cam you have. Those 'R's have nothing to do with the grind. You have not mentioned what bike/engine you are repairing so it's difficult at best to provide any REAL info. If the 'F3' cam is in fact a F3 cam, which we are not sure, it will be a better cam than any of the other stock cams. Prior to that you will find that the (early ?) K0's and the F/F1 and K7/K8 had the hottest cams. 

So compare the lobe heights. Other than that you can also degree both of the cams to determine durations, actual lifts and check lobe centers.

As far a lopey, I have run a Yoshimura Daytona Special cam and I am currently trying a Megacycle 125-75 but with less than 20 miles which hasn't been tuned yet and neither has been lopey. The Yosh would idle down to 600-700 rpm and so far the Mega seems smooth too. That being said both cams are serious top end cams. There are many things you can do to these engines as long as you have deep pockets and know the right people to use.

[garyS-NJ]

Yes, My bike is a 1978 cb750F3 Supersport and I took out the R2 cam.  I'll measure lobe heights on both cams tomorrow and maybe I can get an approximation on the relative lobe placements/duration.  thanks.

[garyS-NJ]

Not wanting to pollute the forum with same posts everywhere, I posted an update on that old 2009 R1 Cam thread.   I didn't see tons of posts on cam markings but will look some more.  I could repost the meat of it here if that's better??  Also as for gasket sets, I'm hearing cycleX gaskets can't be beat.  but also saw gaskets from Vesrah, Athena, RPM, and I bet there's many more.. comments?  And what about guides, I didn't take the head apart yet but read about the F2/F3 guide problem.  Again, CycleX guides?  and my cam chain bumper (that piece in the jug set) and the tensioner pad look pretty beat.  wear to get replacements>??

[flybox1]

Not wanting to pollute the forum with same posts everywhere, I posted an update on that old 2009 R1 Cam thread.   I didn't see tons of posts on cam markings but will look some more.  I could repost the meat of it here if that's better??  Also as for gasket sets, I'm hearing cycleX gaskets can't be beat.  but also saw gaskets from Vesrah, Athena, RPM, and I bet there's many more.. comments?  And what about guides, I didn't take the head apart yet but read about the F2/F3 guide problem.  Again, CycleX guides?  and my cam chain bumper (that piece in the jug set) and the tensioner pad look pretty beat.  wear to get replacements>??

I went with the APE bronze guides (got these at cycle-x right before their new ones were available) and OEM guide seals.
new cam chain tensioner as well.  you can get the tensioner as a set, or purchase the individual rollers, etc.  The set is nice tho.  i got it at cb750supply.....

[Don R]

Check APE's site for guides and F2 rebuilds also.

[Dunk]

I used APE guides in my K1, they seemed like good quality and I'll use them again. Can't comment on gaskets aside from I used a coated steel base gasket and am not happy, it is weeping slightly. I will be using standard paper style gaskets in the future. No leaks from Cometic standard style head gasket. This is using HD studs torqued to 20 ft/lbs.

Curious about the cam fiasco. I have an R5 cam out of another engine that idled a little lopey, smoothed out around 2500 and pulled hard from 8000 past the end of the tach. Sounds like R5 would be a K2 and up lower performance cam so maybe this one was a regrind as it didn't feel like stock.

[Old Scrambler]

I also posted this in the other 'cam' thread

.......I have 4 F2-3 motors/heads and all have or had R-1 cams indicated on the #3 side of the center-sprocket; PLUS the F identifier on the #2 side of the sprocket. These cams also have small horizontal 'bars' on the casting between #3 & #4.  If your spare parts are within spec.........they should make for a good exchange.

Your central cam bearing races are worn so the cam should be replaced because that is the area of greatest 'flex' and strain caused by the cam-chain.  Yes, you could plasti-gauge the fit when you get new caps or install an entirely different cam-tower.  If the cam-races are within spec.........you might tighten the caps just a bit if they are slightly worn.

I would suggest a 'time-cert' versus a heli-coil thread repair............

While you have the motor apart is a VERY GOOD time to replace the valve-guides and valve seals.   Be sure to re-assemble the stud-nuts in the proper order regarding the copper washers and acorn-nuts. 

[garyS-NJ]

thanks all.  I'll look at the APE and cycleX guides.  and check out that other type of helicoil (the brand I have is OEM Fix-a-thread from an autozone or aid auto.).  And I guess when I get those cam clamps I'll plastiguage it before looking for an another cam.  Any suggestions on cam?

[Old Scrambler]

Thoughts.............a good-condition cam-tower replacement from any motor will assure fitment.........

I may have a spare cam-shaft but would have to 'mic' it...........

A Web-Cam 41A or one of the Cycle-X basic performance cams would be very similar to the F2 unit.

............assuming your pistons and bores are good.............new rings and a mild hone would be nice.

[garyS-NJ]

thanks much Scrambler  ...

I looked on cycle-X and webcam sites and Cycle X site said the stock inner cam journals are 0.006" smaller than the #1 & 4.  This basket cam I have is exactly that with 0.864" on the #1 & 4 and 0.858" on the #2 & 3 journals.  factory spec says 0.864" (I don't measure the 10s) with a service limit of 0.8618.  So I'm wondering are my 0.858" journals small or not.  funny I can see the #3 journal has very little wear (I can see the factory finish) so I'm pretty sure it was machined at 0.858".  I probably won't need your cam if this pans out... I'll call cycle X to confirm,

Also, my two manuals say to replace the journal caps with towers as a matched set (WHAT!!??), but I don't have the caps and haven't found them sold online..

lastly, my cam chain rollers and the long pad look pretty beat so I plan to buy the OEM kit from cycleX but their site and webcam says one must degree the cam when changing the rollers..  I don't have the set up and wonder if this is overkill.  Oh, and while I'm at it, should I change the cam chain?  it's hard to measure cam chain wear..

and on those time certs?  do you know the drill size and is the tap a standard size tap?

[Old Scrambler]

Yes,..................you should replace the cam-tower with the caps from that tower.  They were 'worn-in' as a set and will best serve a replacement or new cam.

No for me regarding the sizes for the time-cert..............I have a friend with those tools and pay him for the work. I have a zero failure rate with time-certs.......in motors and for mirror-thread replacements in perches.

[garyS-NJ]

Hey scrambler I don't have the journal caps for the replacement towers. I could use one of my old towers with caps but need a second.  I figured the supersport with different valves and valve angles would have a different tower but if not then I found some k motor towers on ebay.  Will check parts list p/n's tomorrow.
What about degreeing my new set up?  With a new tensioner need I degree the installation?  (I'm not going to the track).  &should I get a new cam chain? Bike isn't here but I think my odometer was around 20k miles.

[Old Scrambler]

Forget the 'valve-angle' BS....................the valves are shorter to accommodate the higher dome in the chamber.

Yes to new chain and tensioner parts.

You may have to degree the cam..........depending on what type you select..........instructions should come with the cam.  Most important is to set the ignition timing to correspond with TDC.

After you have the motor running, check the adjuster clearances on the valves, and then again after a few miles........not thousands of miles.   Hopefully you have freshened the valve-seats, lapped-in the valve edges, replaced the seals and the guides..............and checked the cylinder and head surfaces to be sure they are flat.  Try not to scratch the head surface on the tops of the studs when re-assembling. 

[garyS-NJ]

much thanks again Scrambler.  I found  the '78 750F cam holder P/N 12010-410-000 same as the '78 750K P/N.  and a '76K showed the same P/N with a note that it replaces the 12010-300-040. and 750K3-5 use the  12010-300-040...  so does seem I could use either P/N and do you know the difference??  (is one markedly better?).

And yes definitely put in a new chain even tho I'm not splitting the bottom and so using the the old bottom sprocket (and one of the used top sprockets)  I was thinking maybe old sprockets kill new chain worse than the old chain..

And cam?  If I confirm with Cycle-X site that the inner journals are supposed to be 0.006" smaller than the outers than my basket cam with outer journals 0.864" and inners at 0.858" is nominal and I'll use it.  But definitely using a new tensioner set so still wondering if degreeing is required.  I can't imagine the factory ever did it.

thanks on the other stuff.

[MidnightLamp]

There's a long thing on cam holders and shafts from hondaman. IIRC, the part number change is for the rocker shaft set screws.

[garyS-NJ]

thanks midnight.  Do you have the link to that?  My rockers are the later ones with set screws and this early cam holder doesn't have the rockers so I'd be looking to retrofit my late rockers into the early cam holders.

[Jerry Rxman Griffin aka MuthaF'er]

No degree wheel on a stock cam is necessary, only if you have another intent.

The 'bottom sprocket' is part of the crank. You can not install a new cam chain without using a master link unless you open up the bottom end to loop it around the crank. A new cam chain would be nice but I'd almost tell you to use the new tensioner and go with what you have unless there is OBVIOUS issues.

You can get a new Camilla Tsubaki heavy duty cam chain for half the price of a new one.

DO YOU HAVE A MANUAL??!! There is a download on here if you need one. I'm thinking from some of your questions you need to do a little studying in addition to all the practical knowledge on here but keep throwing out the questions. 

[garyS-NJ]

Thanks jerry.  I have a Clymer &a shop manual and have been reading as much as can balancing other things.  The Web - cam site says degree if you install a new tensioner.  I understand a cam chain with link. Didn't think about the drive sprocket as part of the crank.  I'll keep the old chain and move the cam sprocket to other cam.  And forget degreeing.

[Jerry Rxman Griffin aka MuthaF'er]

If you are planning on using an after market cam vs a stock Honda cam degreeing it would be a real good idea for performance purposes. I initially installed my Yoshimura Daytona cam just like a stock cam since it used the same cam billet with the notch. My first time. It worked but probably could have performed better had I degreed it. Maybe I was just lucky! If it is more radical then you need to be sure the valves don't kiss the pistons too. Keep reading those manuals AND asking questions! Doing all this the second time is MUCH easier.

[garyS-NJ]

Using a basket engine cam but stock.

[garyS-NJ]

[garyS-NJ]

Cam hold down bolt lifted and stripped head threads.  I have OEM fix-a-thread inserts but scrambler likes time certs.  Hate to spend another $70 for the time certs.

[garyS-NJ]

Actually looking close I see one hold down bolt from the cyc1/2 cam tower has some rounded threads.  That tower was socked down fine. Are these bolts & threads in the head a weak point that get treated to new bolts and inserts all the way around? (Hello time cert kit). The bolts are available but I do have other used bolts from the basket motor.