Help need to interprete compression test results

XJ 550

Dry test

Cyl 1 165
Cyl 2 125
Cyl 3 160
Cyl 4 170

Wet Test

Cyl 1 300
Cyl 2 230
Cyl 3 260
Cyl 4 260

Do I read that as worn seals on Cyl 2?

Is there a good thread on next steps? ( I am guessing engine rebuild is going to be painful for a novice.......)

 

Was the dry test done on a warm engine? The dry readings are within spec IIRC.
#2 could just be a stuck ring or a valve out of spec.

 

Yes, on a warm engine......

Doesn't look great does it?

 

It actually looks good. Yamaha calls for 90psi as a minimum. Are your valves in spec?

 

Are valves within spec?

 

I thought the cylinder compression had to be within about 10 % of each other too?

I re-shimmed and everything was in spec but I might just check it all again to be sure to be sure........

 

Having cylinders within 10% of each other is part of the spec, but #2 could be low due to an out of spec valve or a stuck ring (I'm wagering on a ring). I don't see evidence of a rebuild being needed just yet. More diagnosis in needed.

 

ok, great. I have heard about leaving penetrating oil in the cylinder to assist with stuck rings. Does that sound like a reasonable next step?

 

The minimum for a 550 is 100psi IIRC, I'll have to check the book when I get home.

Meanwhile; ALL of the other ones are high, beyond "max" for a 550 even dry. These numbers look like a "wet" test and a "wetter" test; did you already dump some oil in it?

 

No, no oil but.......I failed to get the bike to run dry of fuel..... even with the vacuum tube removed, the bike carried on running when the petcock was in the central position. It did get spluttery but never seemed to completely run out of fuel! Maybe that was the wetness? I can go back to it and take the fuel pip off all together but was trying to avoid spilling fuel on the hot engine.

 

Dark here now so one for tomorrow........... (I need a workshop!)

 

The clymers manual says
Standard 121 psi
Minimum 100 psi
Max 135 psi
For the 550's

Have you tried a different compression tester yet.

 

they do look high to me. I think the max for the 550 is 135. Look into the spark plug holes and see if you possibly have a lot of carbon build up.

 

That begs the question: did a PO "breathe" on the engine?

 

I went to see another bike yesterday (also a 550) and compression tested it. I was getting about 110 on each cylinder using the same compression tester so I think I can rule out a problem with the that.

I didn't understand you k-moe... what is a 'PO'?

Peeing down out there but I'll try to get a light into the hole when it dry's up tabaka45......

 

PO: Previous Owner

aka, pillock that you bought it from
aka, horse's arse that you bought it from
aka, the bloke that had the bike before you that didn't have a clue what he was doing and cocked it all up

 

Oh right, thanks! Just as likely to be me unfortunately.... trying to do things right but making mistakes along the way. Would be lost at sea without this forum!

One thing I have been learning the hard way is to do it right the first time, don't take short cuts or make assumptions. The carb cleaning was a great lesson.

Everything I did before cleaning the carbs, I want to check again and that included valve shims and valve tensioner. Maybe I have made a mistake.

Can I do any harm putting in some cleaning agent down the plugs (think marvel mystery oil or redex) and leaving for 24 hours too see if that affects the compression? Good move?

 

It would be great if others would read this quote and take it to heart! It's GREAT self-analysis that we should all keep in mind.

Dave

 

Fuel shouldn't be the issue. There would be fuel in the bowls anyway, even proper functioning petcock. By all means, take the tank off for your next test. And no matter what, get that petcock rebuilt to avoid future problems with fuel in the crankcase (if any of your float valves ever get stuck open).

Don't know why you are getting such high readings, never have heard anything like it.

But if bike runs reasonably well, you can put a couple of hundred miles on it and see if that will loosen the rings on cylinder 2. I put seafoam in mine and ran it in there for 30 miles as well. Putting kroil in the cylinder for a few days helps as well. Kriol and Marvel mystery oil in the cylinder will not hurt anything at all.

 

It's giving high readings because it's "wet" somehow; there is either gas or oil in the cylinders in enough quantity to raise the test results.

 

I suppose it has to be something like that Fitz. That got me wondering, what about the oil level? If the petcock was malfunctioning and fuel worked its way into the crankcase raising the oil level very high, can that have a bearing on the compression?

 

Oil level in the window on the crankcase looks ok................. and ill take the tank off later and try again.

 

Heck, do it with the carbs off as well. That will completely eliminate that possibility. Once the carbs and spark plugs are off, just crank it a few cycles when all the plugs are off as well to clear out anything in the cylinders before doing any compression tests.

 

rain interrupts play again....

just had time to wip the carbs off run it tell it cut out (amazed how long it can go just on the fuel in the bowls - several minutes)

tested cyclinder on and got 170 psi so pretty much as per yesterday.

looked into each hole and it looks like it has a good coat of carbon in there and looks a bit wet. Gently scrapped a bit with a long screwdriver and it was black crumbly carbon deposits.

Feeling the pipes when warming her up, I noticed the one from cylinder two took longer to get warm and didnt get as hot. Thats also the cyclinder wih the lowest pressure reading albiet still high.

Hoping rain will stop and I can go check the valves again.

 

Today revealed some more information:

The valves are in spec exept an inlet valve in cylinder 1... this is now in spec.

Valve Chain Tension re-set.

Swapped Coils and found that the cold pipe followed.... Concluded bad coil or at least HT lead so ordered a pair second hand (fingers crossed one will be ok).

I put some REDEX engine cleaner down the plugs and left for an hour. Cranked over and soaked up what came out of cylinder 4 but nothing shot out from 1, 2, or 3. Not sure if it managed to escape?

Fired up again and didn't see the clouds of smoke I was expecting.

New compression test which I did running the bike with fuel off until it died but results STILL look wet:

1: 175 2: 130 3: 170 4: 175

Put in some REDEX again to leave overnight.

So, looks ore likely to be stuck rings than valves, is that right?

 

Stuck rings would show up as low compression, so the rings on #2 may be stuck. I still suspect that engine work was done at some point to bump up compression. In looking at the bike have you noticed any fasteners that were drilled for safety wire?
The only other cause I can think of would be a significant build up of carbon on the piston crowns.

 

Imo whatever is going on in there needs to be visually inspected. With all that's been advised and the fact that the compression numbers are not being consistent i'd "hang the chain" (remove the head) and do a visual inspection. Then he'll know for sure what it is and can fix it. Seafoam cleaned pistons and rings, lapped in and spec seated valves, new stem seals, might need a new head gasket; button it up and it should be straight for a good while.

Gary

 

What is safety wire for k-moe? Right now I don't know where it would be attached. Interesting that someone may have done something already, just a shame that one cylinder is out of kilter with the others.

I kind of like the idea of having to go in and inspect.... I wouldn't do it unless it was needed but I know I will learn a lot (never tried before). Well, actually about 25 years ago I helped my dad fix a burnt valve on my Morris Minor and remember thinking he was God, cos I would never be able to do it. Maybe that's why I am drawn to doing this.... As a dad myself now, time I stepped up!

Are there any good step by step guides for this..... idiot proof ones! Also, will I need any specialist equipment?

Thanks for the support fellas.

 

Safety wiing is used to keep fasteners from loosening themselves, and is required by the majority of racing organizations. The presence of holes in external fasteners would be evidence that you have a former race bike that was put back on the street. It's not too common, but I have looked at a few bikes that turned out to have been raced.
Keep in mind that your high compression numbers could be due to carbon buildup (though that is a lot if increase for it to be just carbon, but that does jibe with a possible stuck ring on #2), or to the head having been decked at some point to correct a warpage.

None of that means your engine is necessaraly in bad shape, it just means that you need to find out why the compression is high. I think that removal of the head for inspection is warranted. If it's carbon buildup it will be self-evident, and you can remove it and get it back in running condition. If it's a purposeful compression increase (finding out will require some measuring) then you'll want to run higher octaine fuel so you don't melt a piston, or reduce the compression by running a thicker head gasket.

These are just possibilities. Further investigation must be done to know for sure.

 

Valve spring compressor tool (or you can make one), manual(s), basic bike tools, a camera, note pad and a lot of "attention to detail". Continue to interact with this forum and you'll get there. A idiot would run the bike knowing something is farked. You're not a idiot.

Gary.

 

Thanks guys,

Fish and finger sandwich and a manual for supper.......

Thoughts on doing this leaving the engine in the frame versus removal?

Removing means I could work indoors out of the rain but then I will have to face the broken exhaust studs on pipes that havn't leaked yet! Also sounds more scary!

 

Anyone able to recommend whether I remove the engine before taking the head off or just leave it in the frame? Thanks, Stuart

 

I think that there enough room to remove the head in situ, but I haven't had a 550 apart to know for sure.

 

A 550 I bought had similar compression numbers due to carbon build up, it burnt a litre of oil per 1000km as well

You can remove head and barrels with the engine in the frame on a 550