Low compression on 1 and 2

[Sweeney67]

Greetings from across the pond!
OK I got my XS11 in November last year as a non runner that had been imported from Minnesota. I've now got the bike up and running pretty well and looking fantastic. The only issue I have is that the compression on cylinders 1 and 2 is way down at less than 4 bar (about 50psi) but on 3 and 4 it's like a new bike at over 10 bar (150psi+)
I have no way of finding how long she was laid up before being brought to Scotland so I suspect either fouled valve seats (most likely) or stuck rings. I'm treating with sea foam and running to try and loosen things up/clean the crud out but have only done 45 miles so far with no improvement.
How many miles should I be doing before considering doing a head/ring job? Or is there any other running techniques that may help?
Hoping someone out there has overcome these issues and can advise.
Cheers
Sweeney

[Tenorman]

Check the Valve Clearance...

Hello Sweeny 67,

Hello and welcome to the curse of the XS1100...LOL

You didn't mention this, but my first thought would be to check the valve clearance...

My bike with 31,500 miles had never been checked...I know this because I knew the original owner (who purchased it new).

You might try a leak-down test...that will save you from removing the valve cover...at least for the moment...

Just a thought...have fun!

Tenorman

[Sweeney67]

Thanks Tenorman, that's a really valid point. I havent actually checked the valve clearances yet because there is definitely more valve 'tappet' noise coming from the left side which (and please correct me if I'm wrong) indicates to me that the clearances are wide which, in turn indicates that one or a number of valves are being held open slightly by crud on the sests. Or am I totally off target? I'm just trying to avoid getting into the motor too deep too quick if it's not necessary. Strange that compression is so different between 1 and 2 against 3 and 4

[motoman]

Definitely check valve shim clearances FIRST! Then put several hundred miles on bike THEN re-check those compression numbers. My bet is those compression numbers will be back up to 150+p.s.i.

[TopCatGr58]

Hey there Sweeney,

Okay, are you running the SeaFoam in the gas or in the oil? Hopefully not in the OIL!
To help loosen up stuck rings the stuff you want to put IN the OIL is Marvel Mystery Oil. SeaFoam can break down the lubricative properties of the oil too much and could lead to bearing damage, similar to getting fuel overflow into the cylinders!

Your logic sounds good with regards to the noisier 1-2 cylinders possibly due to excessive clearance, possibly due to carbon buildup on the valve/seats. Another old trick to help clear out carbon while it's running is to spritz into the carb inlets water vapor. YMMV, plus not sure how well it would remove carbon from the valves vs. just the piston.

Aside from a leakdown test, you've done the compression test, but you didn't mention adding a spoonful of oil into the spark plug hole, rotate slowly a few turns , then repeat test. IF rises considerably, then indicates non-sealing rings. If doesn't rise much, indicates poor sealing valves. Can help you better determine when/if you want to pull the head to do a valve job. It can take several hundred miles of running to re-breakin the rings, once they are loosened up(Marvel Mystery Oil).

BTW, the clearances will usually reduce with age/running because the valves get hammered into the head/ the seats get hammered deeper into the head which actually reduces the valve clearances!

T.C.

[MPittma100]

Low Compression

Running the bike with a "magic" additive in the oil or gas and thinking it is going to correct itself is wishful thinking. Run a cylinder leakage test to verify where the lost compression is escaping. Make corrections as needed.

Leaks can occur at head gasket, valves, or rings. Don't want to run the engine if valves are staying open. 15% leakage is considered normal.

[DiverRay]

If you have seafoam, spray a LOT into one and two when the engine is warm/hot until it stalls. turn it off for ten minutes then restart. DO NOT DO THIS INSIDE THE GARAGE!! At restart, once running rev it up to about 3K for 15 to 20 seconds, then let it idle. You will see the smoke and junk come out of the exhaust, but it should clean most of the buildup out without burning a piston.

[Sweeney67]

Oops, forgot to say that after establishing that I had low compression I put engine oil into the plug holes, replaced plugs and spun the motor with leads removed. There was no difference in subsequent compression readings so that's one reason I'm concentrating on the valves.
The bike only has 16000 miles on it and although the tyres had actually perished through inactivity by the time I got it there was no sign of the it having had any rough treatment while on the road. I'm thinking it's a bit premature for a head gasket to go by this time under normal use or for valves to get bent - rather than just fouled.
I'm curious as to how much Sea Foam is 'a lot'? I have been introducing it via a rig connected to the vacuum takes offs on the head inlet rubbers when idling the switching off an leaving for half hour.
I've done this a couple of times and as I say, run the bike for 45 miles but so far there's no compression improvement. I have heard that it may take up to a thousand miles for this to change, do you guys have any opinions on that?

[skids]

16000 miles or KMs seems like pretty low mileage. If any shim clearances are tight, maybe this has something to do with "break-in" from the factory set-up. If any are found to be on the tight side, it will make the valves stay open longer. From what I have been told, longer duration can burn valves. I would be inclined to check clearances, make adjustments if needed, and put a 1000 miles on it. PS, you do seem to know what you are doing, but remember to hold the throttle wide open when doing compression readings.

[Sweeney67]

16000 miles or KMs seems like pretty low mileage. If any shim clearances are tight, maybe this has something to do with "break-in" from the factory set-up. If any are found to be on the tight side, it will make the valves stay open longer. From what I have been told, longer duration can burn valves. I would be inclined to check clearances, make adjustments if needed, and put a 1000 miles on it. PS, you do seem to know what you are doing, but remember to hold the throttle wide open when doing compression readings.

Thanks Skids,
I've had experience of dropped valves on an air-cooled VW motor at 60mph which didn't end well so am paranoid about tight clearances. The only thing that makes me cautious about setting valve clearances at this stage is that if there is crud on the seats that burns off after the valves are set then they could end up really tight. The dilemma I have is that if I leave things as they are and just run it then I might risk burning the valve stems. I hope I'm not misguiding myself although there's definitely a more pronounced tappet rattle from the left side of the engine which suggests that the clearance is too large than too tight.
Whilst I know about having the throttle needing to be wide open when doing the compression test, I dont know why. Are you able to educate me?
Thanks again
Sweeney

[skids]

You hold throttle open so that the throttle plates are out of the way, allowing free air flow for an true compression reading.

[LoHo]

I learned this on a different engine, but...
One and Two are the low side when the bike is on its stand, and might be more subject to water and rust. 16,000 might not be enough to crud the valve stems or seats with exhaust debris, but rust might do it. A Minnesota bike, sitting in cold and wet winters...just sayin'...

[donebysunday]

I would be hesitant to do any valve shimming at this point. I would take short rides so as to not over heat. Good gas with 3 oz. MMO per gallon, keep checking compression after every 5 rides or so. Keep notes on each cylinder to watch for changes. If compression improves your on the right track. JMO
If it shows no improvement, could be someone was in there and did a poor job of shimming.
A leak down test helped me find a very small leak in a head gasket long ago. Thought to myself check the torque on the head bolts, none were tightened as they should be, and the head gasket was no good anymore.
On another I went from 90s to 110 lb. compression variances, half way through the summer 120-140 by end of summer 145-150 next summer 150-155