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No compression

Ray.

Just got it firing!
Joined
Jun 19, 2016
Messages
21
Location
Bristol, England
After recently breaking down a getting recovery home I've finally had the chance to look at my Stelvio. When it broke down it was an immediate loss of power. It felt like a valve was burnt out/leaking. I've just put s compression tester in it and there is no compression on the left hand cylinder.

The question is, before I pull the head off, are there any typical problems I could check for first?

Thanks in advance.
 
What John says above, and drain the engine oil and see what you find. My guess is a wiped cam/lifters. If you have a roller engine, let us know the complete history and what you discover.
 
What John says above, and drain the engine oil and see what you find. My guess is a wiped cam/lifters. If you have a roller engine, let us know the complete history and what you discover.

Ray -

From your past posts, it looks like you have a bike that had the original cam recall (as did my 2009) but still has the flat tappets.

If that's true, your problem is probably related to that, although I'm not quite sure how a wiped cam could result in zero compression readings .... ? An expert may know.

Checking your valve clearances will tell the tale ....

Lannis
 
that, although I'm not quite sure how a wiped cam could result in zero compression readings .... ? An expert may know
If you're trying to call me out... The cam issue would mean ring/cylinder detoriation/wear from fragments and/or lack of oiling.
 
If you're trying to call me out... The cam issue would mean ring/cylinder detoriation/wear from fragments and/or lack of oiling.

OUCH! "Call me out" has a sort of connotation I certainly wasn't implying .... I was just wondering how a sudden loss of compression could be caused by a valve not opening due to cam/tappet failure. When I've checked compression on cylinders where a valve was always closed for some reason, it always showed reasonable compression ....

Lannis
 
OUCH! "Call me out" has a sort of connotation I certainly wasn't implying
Heh, well you quoted me and then said "an expert should know." I've been tinkering and building my own race engines since I was about 11 years old. As I said above, a failed cam wouldn't cause any compression issues with zero lift/the valves closed, but failed rings from loss of oil pressure and metal shavings sure would. ;)
 
Without getting into the middle of it, my first question is did you use a simple compression gauge test? What about a leak down tester, that is a little fancier but has the advantage of often pointing to where your issue is. If an intake valve is leaking badly you will get airflow into the airbox. If an exhaust valve is leaking you will have airflow into the exhaust pipe. Air coming out the crankcase breather can mean rings.
If you did a simple compression gauge test, make sure you held the throttle wide open during the test. You might even want to make sure the throttle for that side works. When you say it had "no compression", do you mean zero compression or just not much?
 
Heh, well you quoted me and then said "an expert should know." I've been tinkering and building my own race engines since I was about 11 years old. As I said above, a failed cam wouldn't cause any compression issues with zero lift/the valves closed, but failed rings from loss of oil pressure and metal shavings sure would. ;)

Well, sorry it came out like that. I guess I use the same style of "writing" on all of the forums I visit, without thinking much about the connotation of the words I use and how they might be different on different forums.

Rest assured that after buying your suspension components, wheels, and engine parts over the years, you're my "go to" guy on anything I'd like to upgrade on my Guzzis, and anytime anyone asks about it, I point 'em over here to GuzziTech .....

Lannis
 
Perhaps you will get lucky and you just need a head gasket. When the engine is running how much blow-by do you have at the dipstick tube? Personally for your sake I hope it is a gasket. Likely the cheapest and easiest to fix.
 
Hi guys, still working on this...

Today I took the cam shafts off, clamped the head back down and checked the compression again. I am now getting a reading on the gauge of around 200 psi instead of 20. I can only guess tappet adjuster has moved and a valve is staying open? When I put the shafts back on the compression went again. I should have turned the engine over manually to see if the valves closed completely but do to poor weather I didn’t get the chance.

Can I assume I am looking in the right area?
 
Did you measure your valve clearance when you opened it up? That would be useful to know when trying to figure out if your valve train / tappets failed.
Also, if you are using a typical compression tester gauge you need to hold the throttle wide open when running the test. Not holding the throttle wide open will reduce the reading, if the throttle is closed the reading will be very low. Always have the throttle wide open when running a compression test.
A different option is a leak down tester. That you run without spinning the motor. You put the piston at top dead center with both valves closed and you put compressed air into the combustion chamber. the tester will measure how much of that compressed air is leaking out. A nice advantage of the leak down tester is it can tell you where the air is leaking from, which can tell you what is wrong if there is an issue.
 
Hi guys, still working on this...

Today I took the cam shafts off, clamped the head back down and checked the compression again. I am now getting a reading on the gauge of around 200 psi instead of 20. I can only guess tappet adjuster has moved and a valve is staying open? When I put the shafts back on the compression went again. I should have turned the engine over manually to see if the valves closed completely but do to poor weather I didn’t get the chance.

Can I assume I am looking in the right area?

You are but I can't really see an adjuster getting tighter but it is possible if they were set at the wrong TDC. That being said, the bike would not have run from that adjustment. I am wondering if the timing is off.

Put it at the correct TDC and check the valve lash before you do anything else. Easy check is when it is a TDC, all the rockers should have some play up and down when you pull on them. If all the lashes are correct then test it again. You need to get the head back to a proper starting position before you try to investigate.
 
To expand a little on what canuck said, if your valve train is failing the clearances typically get looser not tighter.
 
Hi guys, still working on this...

Today I took the cam shafts off, clamped the head back down and checked the compression again. I am now getting a reading on the gauge of around 200 psi instead of 20. I can only guess tappet adjuster has moved and a valve is staying open? When I put the shafts back on the compression went again. I should have turned the engine over manually to see if the valves closed completely but do to poor weather I didn’t get the chance.

Can I assume I am looking in the right area?
I would think that you are looking in the right spot.

Low compression can only happen from a limited number of things. Worn out rings nope you have compression without the cams in place. Failed head gasket nope same as above. Hole in the piston or cylinder wall nope same as above. Burned valves nope same as above. You are losing compression when you reinstall the cams. Compression loss can only be due to the valves being held open by the cams you have proven that. So now you need to figure out why the valves are being held open. Look for the obvious lol that's the things I regularly miss!
 
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