Low compression on 1100....

[Newbee]

Finally gettin around to working on the 1100...got it runnin' but runs terrible. Carbs rebuilt and valves adjusted. Did a compression check and find my problem. 120 in 4, 90 in 3, 85 in 2 and 70 in 1. Not good of course.

As I recall I set valves for .013mm which looks to be on the loose end of spec?

I am trying to determine without pulling head what might the problem be?

The 1100 is a 1980 vintage 4 valve 20 bolt valve cover. I have a 1980 vintage 750 4 valve 20 bolt cover spare motor. If I determine the head is bad can I bolt on the 750 head?

[doctorgonzo]

I doubt the head is "bad", the valves might not be seating well, and the head might need rebuild, and/or you might need rings. You are lucky in the sense that parts for the 4 Valve 1100 are more available and less expensive (because aftermarket stuff exists) than for the 2 valve. I think the procedure is to put some oil in the cylinder and see if the compression jumps up (do a search), I think that indicates rings.

[not a biker]

with that many cyl low it might be the rings. with each cyl at TDC comp stroke ,if you have a air compressor put air in the spark plug hole and listen for air leaking out the carb or the exhaust pipe. if you have a bad valve seal at the valve seat it will make a lot of air leaking sound from the intake or exhaust valve. if no air is escaping past the valves it prolly will be the rings.

[almarconi]

If the engine has been sitting along time the rings could be stuck. Try putting some marvel mystery oil in the cylinders and letting it sit for a while. Did you do the compression test while the engine was hot? Need to hold the throttle wide open when doing the test.

[Newbee]

A few tests done...

Compression readings were with engine hot and throttle open. I will try some oil in the cylinders and see how much if any compression raises. I did a cold check also and readings were on the average 10lbs lower per cylinder.

Engine did sit a long time and could be stuck rings so I guess I could put something in the cylinder to maybe free them up.

[Newbee]

Compression up-bad or stuck rings?

Did a wet test on cold engine all cylinders exlcuding number 1 went pretty close to 150lbs. Number 1 staying around 90lbs.

Put a couple tablespoons of Marvel Mystery oil in each cylinder and will let it sit for a week or so I guess?

Where do I go from here?

[chef1366]

How long did this bike sit? If a long time the rings might seat.
I'd recheck the valve clearance on #1. If it's ok the valves aren't sealing.

[doctorgonzo]

How long did this bike sit? If a long time the rings might seat.
I'd recheck the valve clearance on #1. If it's ok the valves aren't sealing.

Mildly off topic.....

The 1100 salvage head I got, when I tore it down, a hose clamp had fallen in the spark plug hole and blocked open one of the valves. I'd bet my 401K that's how it wound up in the salvage yard.

[tkent02]

Finally gettin around to working on the 1100...got it runnin' but runs terrible. Carbs rebuilt and valves adjusted. Did a compression check and find my problem. 120 in 4, 90 in 3, 85 in 2 and 70 in 1. Not good of course.

Not good but well within reason for a good engine that has been sitting way too long.
Do the Marvel Mystery Oil thing, recheck for a tight valve clearance, get it running as well as you can, and ride it. It should run half-assed OK at normal riding RPM with those numbers, might not idle too smoothly.
Ride Long and Ride Hard. After a thousand miles or so, check the compression again, it might surprise you.

[Newbee]

Sounds like a good idea

I will recheck valve clearence on number 1. Let the Marvel mystery oil try and do its thing.

Is there any other type of "goop" I can put in cylinders to aid stuck rings?

I'm in MT.... so I got awhile until riding weather comes along.

[SqDancerLynn1]

People sometimes use transmission fluid. Make sure to crank the motor a few revolutions before putting the plugs back in..

[rapidray]

Take the motor out of the bike & ship it to me with $7000.00! I'll have it back to you in 5-7 weeks & GUARANTEE it will be 1400 ccs & scare the CRAP out of you! It will run REALLY good too! Ray.

[chef1366]

Take the motor out of the bike & ship it to me with $7000.00! I'll have it back to you in 5-7 weeks & GUARANTEE it will be 1400 ccs & scare the CRAP out of you! It will run REALLY good too! Ray.

A couple of extra zeros there Ray?

[rapidray]

A couple of extra zeros there Ray?

Not to do it right! Push button start, 200 at the back wheel, crank, clutch hub, block, pistons, cams, carbs, headwork, trans work, etc, etc... Ray.

[asetech]

Im with not a biker. Put it on tdc, put compressed air into cyl. then listen if you hear a hiss from exhaust your exhaust valve is leaking, from carbs intake is leaking, from oil fill cap rings are leaking.