SOHC.co.uk Forums > CB750
Help! What's caused this?
Johnny4428:
Devastating! That’s enough to make any owner of a newly built engine check their camshaft and rockers.🥵
K2-K6:
We don't know in this case yet if it's been through any type of blast process.
Certainly I'd not subject the interior of these engines to blasting of any media type. It brings too many questions that don't need to be considered.
The gasket faces for one, any bearing surfaces, any interior paint Honda used to prevent oil seep from original material porosity etc.
Completely enclosed, assembly with all ports plugged, all bolts substituted (unless you're going to subsequently plate them ) then I could see a case before then dismantling and refinish of outer surfaces.
Bristolbadger:
--- Quote from: Trigger on March 25, 2022, 11:31:12 PM ---
--- Quote from: Bristolbadger on March 25, 2022, 07:36:56 PM ---
--- Quote from: Nurse Julie on March 25, 2022, 05:22:32 PM ---I suppose in theory, even though oil is observed getting up to the cam on a newly rebuilt engine at initial start up, it could take a few miles of riding to dislodge any debris that is in the bottom end, such as the dreaded silicone sealer, blobs of glass bead etc, etc.
--- End quote ---
Julie I reckon you're spot on and this is what happened. I'd been pretty surgically clean and really tried to make sure all oil routes were clear but I guess something somewhere blocked a jet and gave me the two fingers!!
So painful to fall on the last hurdle like this after a couple of years but I guess I'd be looking at ANOTHER tear down of the head etc anyway even if I'd discovered the oil blockage before meltdown. Just this is now even more of a costly one for parts and it now not going anywhere (will cancel my insurance on it now as it's just started) and almost beyond me putting anymore into it, moan moan f@#k s@*t
--- End quote ---
If when you strip the cam towers off and the oil jet is not blocked then, you have to look at the oilways in the towers. A lot of owners forget to check the oilways in the towers. When you find out what caused the problem and rebuild, when you start the engine do so, with the tappet covers off. This way you can see if oil is feeding the cam ;)
You have not said, if the engine was media blast cleaned.
--- End quote ---
No media blasting was done just careful pre cleaning of all components with cans and cans of parts cleaner on assembly. When the head and block was off initially I degreased them, washed, then steam cleaned all the hard to get to passageways before spraying out with parts cleaner before assembling
I was double careful of all the tower oil passageways, metering jets ×2.
When I got the engine the bottom end was together just the barrels and head taken off, it had been taken apart by a friend who was a careful and had covered the opening with bubble wrap. I should have probably flushed out the crankcase then somehow but for some reason didn't. I stripped the oil pump completely, there was sludge on the mesh with what looked like possibly a little of rubber hose shavings... I later had to split the cases to get to the gearbox so made sure that whole area was spotless as could be with careful cleaning of the inside cases and with all remnants of the pervious sealant got rid off.
I wished I'd maybe used a cheap light engine oil and changed it after a few initial start ups/miles to help just flush the system then used the decent 15/40... might have spared this pain but maybe wishful hindsight thinking... F*#K!!!!!
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Oddjob:
At least it's a 750 and is repairable, if it was a 500 you'd have ruined the head, cam and camcover. Count your blessings, could have seized when you were riding it.
McCabe-Thiele (Ted):
A very disturbing / scary post it will be informative to read what you find was the cause of the oil starvation.
If you are like me after beating yourself up you will find the cause and get it sorted best of luck with the investigation.
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