Low compression

[MarioR]

Evening,

So just took another project, fj1100.

Bike has uni pods and cone air filter for crank case. After rebuilding carbs and first start,
I noticed some smoke coming out of the crankcase vent so I did compression test.

Cylinder #1 120, Cylinder #2 85, Cylinder# 85, Cylinder#4 85

Well, not really optimistic number that I can see but hoping that can be restored.

So first thought was seized up piston rings. Did soak it 48H in sea foam and compression barely changed, maybe 5 psi, that's all.

Wondering before end I end up with new motor or rebuilding top end, what other successful method you guys use to save the motor?

Thanks

[red]

MarioR,

If the engine runs, you might try Yamaha's Ring-Free fuel additive.  Yamaha makes it for use in their marine engines, but riders here have had some good success with it.  Not sure about a static soaking process with either SeaFoam or Ring-Free, but that may help; I don't know if that has been tried before.

I would want to add a little oil to each cylinder, to replace what the additive strips off, and crank the engine with the starter for a bit before installing the spark plugs.  Good luck.

[Old Rider]

If the bike has been parked for long time it can be sticky rings.
take it for a ride and ride the piss out of it (in a safe way) and check comp again with throttle wide open.

[gdfj12]

I've been using Yamaha's Ringfree since the mid 90's. I usually dose a tank of gas before every other oil change. It helps clean combustion deposits in the cylinders & the rings. It also seems to clean up some of the fuel deposits on the intake valves. I'm about to dose my F150 that's giving me some trouble. Highly recommend it. My engine has been modified a bit (milled cyl. for higher compression, radiused valve seats, cleaned and matched ports, aftermarket valve springs, XJR pistons & rods) so I may be using it more often than a stock engine needs it.

[MarioR]

What I was told bike was running fine before but also sat a bit. How it was running that is unknown....
There is high possibility of stuck rings since one cylinder has high compression and 3 are low. For me it is hard to believe that 3 cylinders with low compression have broken rings... If that was one only cylinder then maybe....As Old Rider mentioned, probably good hard run may clarify if all can be back to normal...
Otherwise, top end will need to be open...

[MarioR]

So now coming to conclusion; if I need to open the top and rebuild it, what are my options:(motor is 1200 probably stock, not sure till open if was already rebuild):
1. If pistons and cylinders are in good shape and in tolerance, just hone the cylinders and fit new rings. What will be the best place to get the rings?
2. If cylinder have scoring than bore it and get new wiseco set? Or other sets available or recommended?
3. Head will need to be inspected, valve most likely redone, seals etc....
4. I will need all gaskets etc - RPM?

Option I will be most economical, option II - digging to full rebuild and most likely bigger bore.
If bigger bore, what you guys recommend?

I still wondering how all 3 cylinder got same low compression and one has high..... Doesn't looks like typical for me. Most time I see one down with broken rings.

[Pat Conlon]

The same 85 pound number in 3 cylinders means something wonky is up with the test results.
I could see 1 or maybe 2 cylinders reading low....but 3? With the same number?

When you did your compression test
1) was the engine warm?
2) did you open your throttle all the way?
3) did you squirt in oil to see if the compression came up?

A leak down test tells you what's causing the low compression:
1) rings 2) intake valves or 3) exhaust valves.

I recommend a leak down be performed before you open your engine.

[fj1289]

I'd Rey the ring free and simply riding it for a while.

If you do decide to go into the motor - might talk to Robert at RPM.  I think they have some cylinders setup already with XJR1300 pistons.  Should be a bolt-in, gets you 1250cc's, and are stock Yamaha pistons so they don't need larger piston to wall clearance like forged pistons and shouldn't raise the compression much. 
Then again, you could also go with a 1350 or 1380 big bore kit ... send the head to JMR here on the list for some porting ... a bit of nitrous ...

[MarioR]

The same 85 pound number in 3 cylinders means something wonky is up with the test results.
I could see 1 or maybe 2 cylinders reading low....but 3? With the same number?

When you did your compression test
1) was the engine warm?
2) did you open your throttle all the way?
3) did you squirt in oil to see if the compression came up?

A leak down test tells you what's causing the low compression:
1) rings 2) intake valves or 3) exhaust valves.

I recommend a leak down be performed before you open your engine.

Hi Pat,

So before I end up opening the top end, I did some work last week.
I did try sea foam and other specifics adding to the oil as well to the combustion chamber directly.
Did some runs and some oil changes. Those are the results after week of hassle:

Today numbers:

COLD TEST (average)
#1 130
#2 135
#3 140
#4 135

WARM TEST (average)
#1 140
#2 140
#3 140
#4 140

ADDING A BIT OF OIL TO THE CYLINDER:
#1 185
#2 185
#3 190
#4 180

Noticed that:
1. Crank case vent - smoke still coming out as soon as warms up and runs
2. Took a run like FJ1289 suggested - bike has power and accelerate hard and fine, there is no issue with running
3. Spark plugs looks fine except cylinder #2 - plug is black that indicates some contingency in combustion. Other plugs are burning correctly.
4. Plugs are new and carb was just re -done and jetted to the system. Starts and runs smooth. No issues.
5. Top of the pistons had a lot of deposit, now after many fuses looks are a lot of is gone.
6. I can say that I hear slightly valves noise, very minimum
7. Valve seals - when starting bike cold I don't see any smoke coming out of the pipe


When you did your compression test
1) was the engine warm? YES, engine was warm
2) did you open your throttle all the way? YES, compression test was done with open throttle
3) did you squirt in oil to see if the compression came up? YES, after adding oil compression number increased

Thank you

[fj1289]

Success!!! Sounds like install new plugs and ride the hell out of it!

[MarioR]

Success!!! Sounds like install new plugs and ride the hell out of it!

Partial success, yes but smoke  from the vent still bothers me......

[Pat Conlon]

Those numbers look fine. Our air cooled FJ's have loose piston to cylinder wall tolerances, allowing for thermal expansion, so blow by is common.

Ride that bike!

Cheers!

[MarioR]

Those numbers look fine. Our air cooled FJ's have loose piston to cylinder wall tolerances, allowing for thermal expansion, so blow by is common.

Ride that bike!

Cheers!

Make sense Pat.

I think if I have nothing to do, I will collect all new parts and build big bore from scratch. It will be satisfied process at least.

Has anyone seen leaking oil from level sensor? I  have checked O-ring and re sealed on the flange it but looks like oil is coming our of the wire???

Thank you

[Pat Conlon]

You could have a cracked post inside the sensor that allows oil to weep.
Good news, new oem oil level sensors are still available
https://www.partzilla.com/product/yamaha/4H7-85720-01-00

I recall in the past RPM also carried these, but I could not find a listing.
Got your ears on Robert?

[RPM - Robert]

We are out of stock currently. Gosh dang the price went up on those bad boys.