No compression in cylinder 3

[edekalil]

Well the l16 I choose to put in the goon has no compression in cylinder 3. It had been rebuilt way back and does not have a great deal of miles on it. When I took it out it was not because of a compression issue. I figured a valve is not seating completely. Took off the valve cover and all looked ok. I could tell it was not running great but figured it has been sitting for a long whiles do might straighten out. Well I guess I will have to take the head off to get it figured out.

[DanielC]

You may have to take the cylinder head off, but first, set number three at TDC, and use your compression tester hose to put compressed air into the number three spark plug hole.  Then listen to the carb, exhaust pipe, or remove the oil cap to hear air escaping.

Sometimes rings get stuck in pistons, and do not seal properly.  One fix for this is to put ATF in the spark plug hole, let it sit for a while, and recheck compression.   If you get some compression after that, try running the engine, and a recheck of compression.

If a valve is stuck open, put a penetrating oil on the valve stem, and allow it time to soak down to the bottom of the valve guide.  This may loosen a stuck valve, and get the compression back up.  

[datzenmike]

To have no compression there has to be a large leak. Even broken rings or hole in gasket will squeeze the air some, enough for a reading.

 

Check the valve lash. As long as the rocker will wiggle it's not too tight. But it may not be fully on it's seat and closed.

 

You could remove the rocker and set the piston well down the bore and using a rubber mallet strike the top of the valve spring. This will drive the valve open and make it snap shut harder, perhaps dislodging an obstruction.

[banzai510(hainz)]

seen cracked valve once on a head sold to me!!!!!!!!!!!!!!!!!

[edekalil]

Thanks for the info. I figure first I'll try the old poor slowly a cup of marvel mystery oil or trans fluid down the carb while the motor is kept at a high rpm to see if that helps it. I saw an old fella do that to a friends truck way back, it looked like the truck that sprayed for mosquitos when I was a kid we would ride our bikes behind it calling if the fog man (I'm still wating for that lawsuits to show up on tv with the law firms of Sakeroff and Sskeroff). Anyway I'll give it a shoot and report back later.

[banzai510(hainz)]

THIDS IS THEW WAY I LOOK AT IT. PULL VALVE COVER OFF.  IF VALVE IS MOVING AND HAS VLAVE LASH CORRECT(WITH LASH PAD STILL THERE ) THEN ITS A HOLE SOEMWHERE IF NOT COMPRESSION..

 

But I seen a moron with a bad spark plug not firing once also

[edekalil]

seen cracked valve once on a head sold to me!!!!!!!!!!!!!!!!!

I had that happen once to, if I don't get lucky first then I will for sure have to pull the head off and then will for sure know what is the issue. Thanks for the input.

[edekalil]

To have no compression there has to be a large leak. Even broken rings or hole in gasket will squeeze the air some, enough for a reading.

 

Check the valve lash. As long as the rocker will wiggle it's not too tight. But it may not be fully on it's seat and closed.

 

You could remove the rocker and set the piston well down the bore and using a rubber mallet strike the top of the valve spring. This will drive the valve open and make it snap shut harder, perhaps dislodging an obstruction.

Mike I believe your right on the money, My guess is that the valve that is not seating was probably open when I last pulled the motor and since it sat so long with that valve open now it is not seating completely. I will give your method a try first and see how it goes. Thanks

[edekalil]

THIDS IS THEW WAY I LOOK AT IT. PULL VALVE COVER OFF. IF VALVE IS MOVING AND HAS VLAVE LASH CORRECT(WITH LASH PAD STILL THERE ) THEN ITS A HOLE SOEMWHERE IF NOT COMPRESSION..

 

But I seen a moron with a bad spark plug not firing once also

At first I thought it had to do with it not firing but when I did a compression check I ruled that out.

[edekalil]

Got to catch up on some guitar work today for some friends( on my vacation as always) but I will squeeze in some time to look at it this evening.

[datzenmike]

Make sure piston is not near TDC. Good luck.

[edekalil]

Well I did not do that yet but did the pour the marvel mystery oil some down the carb at higher rpms where it would not die thing did not go crazy but now it does ideal at about 1000 and does not die. Could not get it to do that befor. Did not do a chech on compression yet but will later. Befor I did the oil down the carb thing I did hook up a air tank to the cylinder with the hose for the compression tool opened up the air and nothing happened had the 3rd cylinder at tdc and no sound or leak I could hear. Did a compression check and it was in the 0 range but it had a very small amount of air in the gauge when I bled it. Also found a vacuumed leak I fixed. I will add a video of it ideling here soon as I can get it up.

 

 

http://s338.photobucket.com/user/ekalil/media/510parts/9FEDB2ED-6866-457C-9F1B-76B5C058953B.mp4.html

[banzai510(hainz)]

vid sounds normal to me was hoping to rev it up.

 

you make sure the valvelash  adjusted? or even on there

[edekalil]

vid sounds normal to me was hoping to rev it up.

 

you make sure the valvelash adjusted? or even on there

It does seem normal in the vid before you could not let down the idel with out having my foot on the gas I guess something is getting better so i will check the valve lash here as well' at least it is now running on it's own ideling. I'll get ya some revs next time.

[datzenmike]

A bad cylinder is less noticeable when revved up. Try dropping it down to 700 or so. At that RPM the mechanical and vacuum advance is likely in. Get it down and then check the timing is what, 12 BTDC on an L16?

 

Adjust the idle mix screw for fastest smooth idle and assuming the RPMs went up, turn back down. Repeat several times until you cannot improve the idle quality and the idle is holding at 750-800 ish. 

 

I've seen worse off engines that only got better as they were driven.

[edekalil]

Will do Mike, at least it is now idling on its on before it would not idle you had to keep your foot on the gas. I figure it will get better as it is used in time. Noe just to get the tank cleaned to get to flow gas to the front to the engine.