Topic: CB750 Camshaft repair

[kaysystems]

This winter the engine will come out of my K0 yet again.

The original camshaft has a gouge in one of the bearing journals, which is also tapered making it undersize.

I will be replacing the camshaft bearings.

I have 3 options

1) replace the camshaft with a K2 model. Don't know what this will do for performance etc

2) Find another K0 cam - no success yet

3) have the K0 camshaft repaired by building up the bearing & regrinding to stock size

Any thoughts, or ideas where #3 can be done?

thanks

David

[GroovieGhoulie]

I would work to keep the K0 cam or find another.  The K0 had a hotter cam than later 750s, with more duration and (I think) a hair more lift.  Even the K1 had a milder cam, and it was downhill from there, (as far as factory engine de-tuning, which continued until the mid-70s, resulting in some VERY mild 750s).  The K0 is the most hairy-chested of the K models and I would seek to preserve that.

[kaysystems]

I guess that nobody wants to give up their K0 cams. Even with a really rattling top end, the performance is much beter than I remember my friends K2 in the mid 70's

David

[eurban]

David- From what I understand, the earliest camshafts were a bit "hotter" than those that followed, except perhaps  those for the F0/1 and K7/K8s and for that matter the F2/F3 cams although I don't know how well those work in a non F2/F3 motor.    If you cannot find a suitable OEM cam, you could certainly purchase a mild Megacycle or WebCam camshaft.  You could also probably have a cam ground to your K0 specs either as a regrind of good stock cam or from new stock. When I ordered my cam from Webcam, they first sourced a new blank and then ground it to the specs that I requested; so there certainly are suitable blanks available. . . . .As to the "hairiest chested" K models,  (sorry if I sound like Eldar) I think their is alot of nostalgia about the performance of the Sandcasts.  The test numbers that I have seen show the K7 and K8 pulling better 1/4 mile times inspite of being a good bit heavier(40lbish).  I don't know whether or not the late cams were tweeked to benefit performance but it would be worth confirming as they should be plentiful.  Good luck

[GroovieGhoulie]

Also, the K0 had a higher redline (8500 versus 8000), which the K0 cam was tuned to work with.  The later cams were tuned more for the midrange while the K0 was tuned more for up-top.

[kaysystems]

From what I read, the later K models were a bit quicker, but they had other mods too. So doing a mix on my K0 may not work. I like it the way it is. Also remember that the K0 has less exhaust backpressure, which can affect tuning somewhat.

Thanks

David

[kaysystems]

Anyone think this is a K0?

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&ih=006&item=160005231077

David

[MRieck]

Why don't you just get a Megacycle 125-05 regrind and get more performance than any stock cam. No matter what all SOHC stock cams are weak...some are just weaker than others.

[kaysystems]

Why don't you just get a Megacycle 125-05 regrind and get more performance than any stock cam. No matter what all SOHC stock cams are weak...some are just weaker than others.

but what else would I need to do? I'm not going to mess with mufflers, carbs, timing etc to get it running. I've just been through all that with the stock setup.

David

[nteek754]

Hey there  what eer you do make sure you  put in new towers do not mix and match  been there done that 20 years ago and what a rotten summer the towers being aluminum get a wear pattern and if you put  differant cam in there gonna make new wear pattern and by then its woen out  if it was me I would get new towers and a one step up from a stock cam did it years ago with an andrews A grind  but dont know if there still around but like in other post there are cams available good luck seven fifty four ever  Craig in Maine

[kaysystems]

Hey there  what eer you do make sure you  put in new towers do not mix and match  been there done that 20 years ago and what a rotten summer the towers being aluminum get a wear pattern and if you put  differant cam in there gonna make new wear pattern and by then its woen out  if it was me I would get new towers and a one step up from a stock cam did it years ago with an andrews A grind  but dont know if there still around but like in other post there are cams available good luck seven fifty four ever  Craig in Maine

Yes I intend to get new towers. What about the carbs & rejetting?

David

[Sam Green Racing]

Dave, I would go with the cam Mike Rieck mentioned, $228 and get Mike to tidy up your ports.

That will transform the performance of your bike without turning it into a racer or putting it under any stress.

You shouldnt have to alter your carbs but what fuel you do put in will flow better.

Sam.

[eurban]

If your bike's  carburetion was pretty well optimized prior to this reworkl, then I doubt installing a mild performance camshaft would necessitate carb tuning.  With a mild cam you wouldn't need to use stiffer valve springs just make sure that your current springs/retainers/cotters are in good shape.  Also, consider why your current camshaft is damaged and correct any issues prior to risking your newly purcha$ed part

[HondaMan]

If you want to keep the K0 cam, then you can check the cam bearings for roundness (they won't be) and align-bore them, then install inserts, and have them cut to match the cam. Expensive, though.

Alternately, you can check the current size of the cam bearings, ACROSS the bearings. The 2 middle ones are the ones that really wear, and they let the cam flex. This makes the top end rattle like an old Model T. Check the dimension across the 2 middle bearings, determine what camshaft journal would be required to get you back to .004" - .005" clearance, and have the cam built back up and turned round to that size. I'm not good enough on my lathe to do this for you, or I'd offer it.

Alternately, you can reverse the bearings in the head (1-2 on 3-4 side & vice-versa). This puts the worn ones on the outsides and the newer ones on the inside. This is the "poor man's rebuild".

[kaysystems]

If you want to keep the K0 cam, then you can check the cam bearings for roundness (they won't be) and align-bore them, then install inserts, and have them cut to match the cam. Expensive, though.

Alternately, you can check the current size of the cam bearings, ACROSS the bearings. The 2 middle ones are the ones that really wear, and they let the cam flex. This makes the top end rattle like an old Model T. Check the dimension across the 2 middle bearings, determine what camshaft journal would be required to get you back to .004" - .005" clearance, and have the cam built back up and turned round to that size. I'm not good enough on my lathe to do this for you, or I'd offer it.

Alternately, you can reverse the bearings in the head (1-2 on 3-4 side & vice-versa). This puts the worn ones on the outsides and the newer ones on the inside. This is the "poor man's rebuild".

I looked at the poor man's rebuild, but the #1 end of the cam is so badly worn it just wouldn't work.
Yes, it sounds like a Model T right now. Also #3 cylinder had a leaking intake valve, although the clearance was slightly wide. I lapped it in, but still sound a little off & the carb needle on this one is higher than the other 3. There are signs of mile backfire through the carb. I need to get rid of the flex in the cam.

According to the specs in my (K0) manual the middle two journals on the cam are smaller to start with, but the bearings are all the same size.
If I don't get a replacement cam (even aftermarket) I'll get it built up. I don't want to have to play with all the settings for another year just to get it running nicely, so I want to keep the original cam.

Thanks for your insight.

David

[Jerry Rxman Griffin aka MuthaF'er]

I hope you see this before 18:05 PDT TODAY. Check out this NEW cam on EBay. It's a -300 part. Listed as 1969-1976 cam. Check item #160005231077.
Jerry

[upperlake04]

According to the specs in my (K0) manual the middle two journals on the cam are smaller to start with, but the bearings are all the same size.

Glad you brought this up - exactly the same situation on my 78 750F.  The journals measure the same diameter on the working surfaces and the small area beside it which doesn't touch anything in use. They must have been manufacured that way.   I read the bearings were factory line reamed, which would make them inline and the same size. The bottom half of bearings 1 and 4 are worn shiny while 2 and 3 are only worn shiny on a  5/8" area at their bottoms.  All the top halves are still matte finish - completely unworn.  I don't understand.

  Can someone explain why it was done this way?

[kaysystems]

I hope you see this before 18:05 PDT TODAY. Check out this NEW cam on EBay. It's a -300 part. Listed as 1969-1976 cam. Check item #160005231077.
Jerry

Anyone think it's a K0?

[HondaMan]

I hope you see this before 18:05 PDT TODAY. Check out this NEW cam on EBay. It's a -300 part. Listed as 1969-1976 cam. Check item #160005231077.
Jerry

Anyone think it's a K0?

Check with a Honda shop, especially the last 3 digits. It might be the one used as a "general replacement cam", which often had the last-made durations, like the F models. Since it would fit and run, Honda did this with a lot of replacement parts.

Kinding a K0 cam might be tough. American Honda swears the cam never changed, but my dial indicators (over the years) know a different story...