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Slight loss of compression and not idling nicely

Just put the head cover back on, Hopefully gasket sealant doesn't ruin internals of an engine if it gets in contact...


I think I had the piston at TDC, pretty close I believe.. and the intake valves had a little bit of clearance but the exhaust valves were rock solid... Maybe I was a tiny bit off because it was hard to kick it over to TDC and stop it but i'l check again tomorrow


Can you take off the ignition cover and turn it over with a spanner?
 
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how did the cam follower bearings feel ?

yes turn engine over with a spanner on the ignition side, its a LH thread
 
Cam follower were the smallish bearings attached to the arms?
They were still smooth and didn't have any grinding bits


I do think that the exhaust valve doesn't have any clearance, Could that cause poor off throttle response and lower compression?
 
yes, tight valves do that

question is .. if the lash was set not long ago why were they tight ?

human error or a failing cam follower bearing or badly wearing exhaust valves/ seats,

if the Clearance tightens up again quickly I would consider the valve/ valve seat as a problem, if the clearance and the compression problem comes and goes look again at the follower bearings
 
The mechanic probably did it wrong, It was serviced in his shed shortly before I bought it... And a few things weren't right with it.

Also he said the clearances were still perfectly fine after 207 hours or whatever it was, Is that even possible? He must have still touched them though... I'll check them again at proper tdc
 
I'm really stumped, all valves seemed fine... And couldn't see any broken springs or anything

Cam follower bearings were still spinning freely and not rough at all


Any other ideas on what it could be?
I'll try to get a video up of what it's sounding like
 
If it is losing compression, it is either something to do with the valve train or the piston. Maybe a piston ring is sticking in its groove.
 
Could pistons sticking also cause backfiring, and slow throttle response?
Or would I be leaning more towards valves...

Is there anything more I can do to see whats wrong, will I be able to tell if a valve isn't fully closing or if it's sticking without pulling it apart?
 
Thanks, I'll try and find someone who can help me with that...

I believe it is valves, purely because it doesn't idle well, sometimes backfires and has poor throttle response....
Would I be correct, or can piston rings cause this as well?

Could it be something like the timing chain? It's done 210 hours, what happens when you timing chain tensioner runs out of clicks?


Here's a video of it
https://www.youtube.com/watch?v=yYyQYMKGXyc&list=UU929TJ0by7MmWbD18D6Vygw
 
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Hi Matt,
You can try the following spray your intake boot with penetratingoil while the engine is running, if it picks up revs, or runs on idle good youre intake boot is leaking.
I don't wan't to scare you,but if it ran on a very lean mixture it's possible that youre exhaust valve are burned.
Because of a lean mixture an engine gets very hot, but it's possible that the coolwater doesn't boil over.
Hope for the best.

Grtz Rens
 
Hi,

I have done up the intake boot quite tight, And I have just replaced it... Never been ridden on
I'll still try it, but I have my doubts


Is it something that can affect compression?
 
mattwilkinson said:
Hi,

I have done up the intake boot quite tight, And I have just replaced it... Never been ridden on
I'll still try it, but I have my doubts


Is it something that can affect compression?
Click to expand...

No
Valvetrain or piston assembly
What about all the decomp assemblies
 
Will a leakdown test be able to tell me if it's piston, or if it's valves or if it's decomp?
Should I put a bit of oil in the head, and turn it over and see if it's piston rings?


Also, if I bought a compression tester, would it be useful at all?
I don't really understand the difference between compression testers or a leakdown test, But will a compression tester tell me if I actually have lost some compression?
 
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I would say get a compression tester. it will tell you the peak pressure, Compair this to a fellow members or buddies bike of the same engine model etc.

Im no expert as im a rotary sort of guy however the only things that could be causing loss of compression would be piston blow by (where the gasses are squeesing past the piston rings into the crank case) or valves not sealing properly.. Tuliped valves?

could you start it and put your hand over the crank case breather on the head to see if there's alot of pressure coming out?
 
Will a tester fit in?
It seems like you have to screw them by the bottom, and looks extremely difficult to thread in since the plug hole is so deep inside
 
It should. They usually have an o ring seal so they don't have to go all that tight. A leak down would be better as you have a decomp on your engine.
 
I think I will remove and clean the carb, Because it's sat for a couple of years... When it was serviced before I purchased it off a mate the carb was cleaned, but it may have gunked up again from old fuel or something else.

Also I think the intake boot was still leaking when he tuned the carb, so maybe now it is running really lean or rich...


How hard is it to remove the carb, Do I need to undo the shock at all? Or do I just remove the intake boot and that'll give it enough room?
 
Hi Matt,
It's a good idea to clean the carb,because the gas that is made today has so much additives,that it's aging very rapid and will clog youre carb.
Also pay some attention to carb venthoses,because they can also give trouble if clogged.
About the compressiontest,normally the spark plug is a 10mm one,so in this case you could take an old sparkplug and carefully take out the porcelain and try to weld a nipple to fit youre compressiontester to it.
Tried and tested it on my Husky TE 510,wich has the same sparkplug measurement.
Compressiontesting has to be done with !! FULL THROTTLE !! so that will be a challenge.

Cheers Rens
 

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