Low Compression

[Johnny]

Hi all

I booked my track bike in to have to work done and they have called and said it is running low on compression on two pistons.

They ran it on the rolling road and said it runs a bit rough at low revs but fine up top.

They also saw it smoked a bit.

Any verdicts on what this may be? They said it could be rings but would need to take apart to have a look and then if it is the rings a rebore would be costly.

Is this thing likly to go bang??

Last time I rode it at Brands it was running fine. If it was on its way out what are the signs?

thanks in advance

John

[Variablevalves suck]

If its on the wayout it will smoke/use oil and pull like a wet fish.
Have you had the valve clearences checked?

[racesupplies]

Might be a good time to start a new thread.
WTD another motor.

[Variablevalves suck]

D'oh!

[CMSMJ1]

Beg borrow or buy a compression tester and check it yourself. Take the readings. Then dribble some oil in the cylinders and retest - if it is a lot better, then it is rings. If not, likely valves - so get them lapped in and go from there.


All is not lost..depends how much time you have and inclination to sort it out.

[racesupplies]

Yes go with that mate,dont take any notice of us,probably be a good time to have a look in there anyway.

[Johnny]

Thanks for your advise guys.

Do you know of anyone who has an engine for sale?

How much do they normally go for?

What would you recomend, buy a new engine of get mine rebuild. Don't want to buy another and have issues again!

[knight1077]

mine was the same and then it went pop turned out to be a f#*@ed barrel did the wet fish and smoking stuff then bang the rebore and new pistons is the best part of 400 squid as the next size pistons are not cheep so dont let it get past the point of no return as i did and am now putting a second hand motor in which took a while to find expect to pay between 200 and 400 for a good one.

[Johnny]

I have picked it up today and does not seem that bad.

I'm not a mechanic, however it still pulls ok.

It is a rough under 4k but above that it is fine. I only got to 2nd as it’s not road legal.

I'm hoping that it may last me a little longer. It has had its valve clearances checked so would it indicate a wearing ring?

The mechanic said that the compression is fine when the engine picks up revs with a little smoke at high revs.