Low Compression

Hi all

I've just had a compression test done and my 3rd cylinder reads 30!!!

My mechanic reckons that it's possible (but not necesarilly probable ) that the ring may be stuck and so I've used a synthetic oil in the slim hope that it may help.

If there is anyone with opinions on this I'd love to hear them.

If the rings need replacing, is it imperative to do the pistons too?
Now, I'm pretty sure I don't have the skill do do this myself so if there are any Aussies out there who can give me an idea on price of parts & labour for this sort of job, please give me the bad news.

Cheers

Sammy

 

It depends on your definition of "imperative"! And it also depends on the condition of the pistons and cylinder walls once you get everything apart.....you'll never know until you do.

A full engine rebuild....which is what you're looking at doing.....is going to set you back around $1500 US. Not cheap..........

I'll assume that the above information easily qualifies as "bad news"?

 

Hi Sam, what did the other pots read? A ring job wouldn't be the hardest job & if it's just the rings, not that costly, but, as chacal says, you're not going to know what you are in for until you get the thing apart.

 

I just rebuilt my engine and I didn't need to replace my pistons. There's a good chance that if you have patience and can read and follow directions, you can do the job yourself for somewhere around $200-$300. My pistons and cylinders were within spec so I just needed a gasket kit, new rings, hone the cylinder walls and lap my valves. After that I needed to re-shim my valves but that's not hard to do and isn't expensive either.

 

WAIT.....

did you check the valve adjustment yet???? if one of those valves is tight its going to bleed off compression.

if the adjustment is good, take out the spark plug, bring the piston to TDC on the compression stroke and pressurize the cylinder with a rubber tipped blowgun.
-if air blows out of the crankcase its piston/rings
-out the carb its the intake valve could be bent/chipped
-exhaust....you got it! exhaust valve issue!!!

 

Comp test results
110 110 35 125 :cry:

 

I feel sick :cry:

 

Ugly. Stay away from tall bridges.........

Zookies advise is good, check the valve adjustment and try to determine whether it's bad valves vs. bad rings. A valve job won't be nearly as much.

 

If the bike has been sitting a while, it is a good bet the rings are sticking. Might want to soak the offending cylinder in some Marvel Mystery Oil, a shot in the sump wouldn't hurt either. If you ride it daily, you gots problems.

 

I think the bike sat for a while, then the PO did a few thousand km in a couple of months, probably without an oil change . I just changed the oil and the filter which were both filthy. I put in Guardian 15-50 semi-synthetic.

 

Run the bike through a few heat cycles and retest. If no improvement and valve clearances are good, you need to do a leak-down test. If that turns out bad, you will need to pull the head at a minimum and a motor at worst.