SOHC.co.uk Forums > CB750

cam shaft oil starvation

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the-chauffeur:
Mouse

Been there, done that - the blocked oilway on one side, that is.  Expensive problem if you don't catch it early . . .

Long story short, I trashed a camshaft because of a blockage in the right oilway.  After some investigation, and much to my surprise, the blockage wasn't in the jet in the head, but was much lower down the engine - it was in the top of the crankcase.  My advice would be don't even think of starting the engine again until you've been able to pump some oil through the engine manually and can watch it flow out the top end.  This is easier said than done unless you've got some way of holding the engine still with the rocker cover off (and preferably with the camshaft/rocker assembly off as well). 

I fitted a kit to the frame of my '72 that allows me to remove the top of the engine while it's in the frame.  When it came to second/third reassembly, I was able to leave the cam train parts off the top, fill the bottom end with oil and then crank the engine using the kick start (which engages the oil pump).  It took a good few pumps, but after a while oil came flowing out the jets, and I only reinstalled the camshaft/towers when I was sure there was a good supply to both sides.

And yeah, you need all four O-rings under the cam towers - the outer ones may sit in blind holes, but they seal the join between the cylinder head and the underside of the towers, which in turn creates the pressure needed to force oil to spray around the top end from tiny oilways in the tops of the towers.  Having said that, be aware that there are two different sizes of O-rings; the bikes up to and including early K2's (I think) had fixed oil jets in the head, and use smaller O-rings than those used on the later K models (which have removable jets).  Check your parts carefully.  You might also want to take a look at Hondaman's guide to modifying the cam towers for better oiling.

I've also found rag bits in my filter in the past.  Mine were bits of polishing mops left over from when my polisher had shined up the engine sidecovers but didn't clean them out when he'd finished. 

Hope that helps.

bluemouse1006:
Hey Thanks

Ive the engine back in now with the rockercover on,as you say it would have been better to check for oil before hand but I was happy I found enough restriction to cause the fault  (there was a little oil getting through. the other link was very good but has made me nervous now about every thing seizing in the future,Im running the bike this summer and will be changing the camchain etc in the winter if the rattle that they all have annoys me enough ..

Thanks again and Ill keep you updated

Amos

K2-K6:
It's really easy to turn these over with the starter motor when out of the frame so you can check oil supply with cam cover off before install.

If you cut the right shape whole in a piece of 3/4 inch plywood. and fix it onto blocks, you can get the engine to stand quite firmly in it. Can be useful when assembling the top-end anyway.

As an interesting point, I've always turned these motors over by hand for the first time after fitting cam etc as you can feel if anything is wrong (I've seen many times bent valve from others using the kickstart or electric) one or two rotations then double check the cam timing before going further.

Hope youv'e got the oil supply sorted now.

bluemouse1006:
Hi

As you can see from my clutch horror story on the other post I have the engine running and seem to have a good oil supply to the top end now just wished the clutch would clear!!
Im going to keep an eye on it just in case. thanks for your help and comments

Amos

ChrisD:
Hello.

Yep can identify with the previous posts, rebuild my K0 in 88 and used to much gasket goo on the cases which got up to the cam carriers and yep blocked the restrictors and blew away a cam and followers, took out the engine and cleaned it all up but this time made sure had good flow by connecting up oil tank and mounting the engine on a dexion frame and turned it over untill oil flowed well to the top end. Refitted and and its still oiling ok. In process of rebuilding bike back to original colour so will have engine apart again to renew primarys and cam chain and anything else that looks suspect.

Cheers all Chris.

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