Cam wear / low compression could they be related?

[Guest]

Afternoon all

It wasnt too cold today so i went out to the garage and double checked the valve clearances I adjusted a few weeks ago and buttoned it back up with a new gasket. I did notice that there seemed to be a fair amount of wear on the cam lobes. The engine is apparently a 18700 Km motor so it shouldnt be like the pics I have attached, should it?

I also did a compression test once it was all back together and I got the following;

1 130psi
2 70psi
3 130psi
4 125psi













Any ideas what might be going on with Cyl 2 and whether it is related to the cam wear.

thanks in advance for any assistance.

[Nessism]

Did you start up the engine and run it to get it hot before performing the compression test? Did you hold the throttle wide open during the compression test. How many miles are on the engine in the recent past? When you adjusted #2 valves were they tight?

Regarding the cam wear, no that shouldn't effect compression. It is a classic problem though with the 2nd generation 750 because the oiling system is weak - spun crank bearings are even more common from what people have said. I strongly advice doing some research regarding the oil pressure relief spring shimming mod. Some guys have talked about this in the archives.

Another thing is to keep so much crap from getting into your engine. Those cams are dirty big time so all that stuff is now going into the engine.

[tkent02]

#2 is the carb which the vacuum line to the petcock comes from. If the petcock diaphragm fails, fuel runs down into that carb, that cylinder then runs very rich. This washes oil off the cylinder walls and thus wears the rings.
Fix the petcock and ride it several thousand miles, the rings should start to seal better, it will likely be OK after that.
The other cylinders are fine, all of the cylinders would read higher at sea level, your higher elevation will make every engine's compression test slightly lower.

[haggisbasher]

Thanks Nessism

I did clean them up as best I could before buttoning it back up but point noted. I have not put any miles on it since i got it last fall, As far as I can tell neither did the PO. I did the compression test cold with the throttle wide open. I am off to research the oil pressure mod.

The bike did start and run before i did the valves but it was fouling the plugs in all cylinders even after running with no choke and no air filter so I suspect the carbs have been fiddled with. I got my berrymans las weekend so the carbs are next on the list.

How much should i be concerned about the compression, I have tried searching and have seen a few posts saying just run it it will be fine, being a noob that sounds better than tearing it down.

Thanks
Tom

[haggisbasher]

Thanks tkent

I new the fasct it was cylinder 2 was significant somehow although I have had the tank off the bike for 8 weeks now and the tank hasn't leaked a single drop on prime or run. I know that the petcocks are a known weakspot so I will look at it more closely.

[Nessism]

Italian tune up needed! Ride the **** out of it for a while and check again. Fix the rich running first of course. If you don't find the info about the oil spring mod after an honest search, ping me via PM and I'll dig though the archives and try to find the reference.

[tkent02]

Try putting vacuum on the line as the carb does when the engine is running. Maybe it will leak, maybe a PO fixed the petcock, I dunno.
Either way ride it, a lot of miles, it should be fine. Maybe a top end rebuild is in the future (like next winter?) maybe not, but get everything else working correctly and ride it.

[rapidray]

That exhaust cam & rockers are JUNK! Ray.

[haggisbasher]

I had a feeling we might get to that.

Thanks Ray

[SqDancerLynn1]

Yep the engine would carbon up and block the oil passages, cook the motor. You might think about looking for another motor

[haggisbasher]

Is it new motor time or could it be saved by a new top end? I cant really afford to buy and rebuild another motor, right now I'm not sure I can afford to rebuild this one.

I dont think theres any point in just replacing the cams and rockers because whatever caused this failure is probably still unresolved. That tells me that at least the head needs to come off and be dipped or whatever the best way to clean out the passages is.

When I did the clearances they were all tight but 1 and 2 seemed tighter than the rest. I presume its possible that there is already carbon build up on the valves of 2 causing my compression issue?

Thanks for all the advice

Tom

[Nessism]

I have no idea what Lynn is referring to with regard to her comment. Cam wear won't cause carbon to form, and carbon can't plug up oil passages anyway.

I suggest you button that bike back up and ride. Keep your radar up for some new cams and rockers and change them at some point down the road - no need to pull the head to do this. Use good oil such as diesel engine oil and don't let it run longer than 2000 miles. And shim that oil pressure relief spring straight away.

[haggisbasher]

Hey Nessism

Thanks for sticking with me on this. Thats kinda the plan I had figured on I have all the other stuff to check before spring arrives so I hope I can ride it a bit this year and assemble the parts over the summer to fix it next winter. I am going to shim that spring but I am not very sure where it is located so I am reading through the manual from Basscliffs site.

First thing I did was change the oil and filter so shes all topped up with Rotella 10w40.

I need to clean the carbs and rebuild the brakes and hopefully some riding this summer will boost the motivational juices for some more major work to come.

On a side note is there a time limit on gasket sets? theres a NOS set for my bike on evilbay right now but he admits they have been in inventory for around 25 years. Do they degrade over time?

Thanks all
Tom

[Nessism]

It was GregT that posted about the pressure relief spring shimming job. You might want to contact him for more info.

http://www.thegsresources.com/_forum/showthread.php?t=146890

As for old gaskets, I don't think that's a problem on the gaskets but I'd replace the rubber parts if they don't feel soft.

[1948man]

[QUOTE=I have had the tank off the bike for 8 weeks now and the tank hasn't leaked a single drop on prime or run.[/QUOTE]

It should flow freely on Prime.