low compression, --inevitable strip down??

so-- I finally got round to checking my engine, during my rebuild.
the engine is on the bench, and has been sat a couple of years, with carbs removed and rags stuffed in the intakes and exhaust.
I got the valves in speck a couple of years ago, and ran the engine, and all seemed fine, no bad noises, or overheating.
so I did a compression test today, and the numbers are---

#1----0
#2----45
#3----100
#4----85

squirted a few presses of the oil can in each cylinder, and now

#1----110
#2----155
#3----160
#4----100

so #1 and #4 still low, so this would indicate stuck rings right?.
before I tear into it, what "magic potions" could possibly free these up.
as you can see from my profile I'm from uk, and the chemicals you get off the shelf in u.s. , are just not available easily here.
cheers,
stu

oh, p.s.
engine has 47k miles

 

A engine that has been sitting for a few years will most likely have a few sticky valves. Your compression numbers show that. Pull all the plugs, put some penetrating oil in each cylinder. Spin it over to mix the oil in and let it set a week. Do the compression test again and see if the numbers improve.

 

I don't trust those numbers.

You should get some compression even from totally shot rings. To truly get zero you need a major valve problem or a holed piston. I suppose a valve sticking partly open could do it too. A shot of oil won't bring those up.

 

use a 50/50 mix of atf and acetone. let it soak a few days and try the comp test again.

CN

 

Bensalf - did you check the valve clearance??

I got a "100" reading on a good motor with a valve way out of spec.

 

Compression readings which improve by adding oil to the hole generally indicate the hole has some Ring Related issue.

If you had a Valve or Gasket-related problem, ... the "Wet-test" would have shown little or no improvement.

 

rechecked valve clearance on #1 today, and in spec at, int= .127mm , ex = .2mm
-----------------------------------------------------------------------------------
Compression readings which improve by adding oil to the hole generally indicate the hole has some Ring Related issue.

If you had a Valve or Gasket-related problem, ... the "Wet-test" would have shown little or no improvement.
-----------------------------------------------------------------------------------
yep, that's why I did it.

so-- redid the compression numbers again today with still a trace of oil in there, and-----

#1----25
#2----75
#3----105
#4----90
so it appears the original numbers were correct

I managed to get some acetone today, (from of all places , a pharmacist)
mixed it with a.t.f. , and put a couple of tablespoons in each cylinder,
as cyclenoob suggested.
so i'll let it sit for a few days, and see how we go.
thanks for your help so far
cheers
stu.

 

so I let the acetone/a.t.f. sit in the cylinders for above a week, and redid the compression test.
#1 was back down to zero, other 3 improved slightly up from original test.
so ,as I said in my original heading "inevitable strip down"
so did just that.


squirted some penetrating oil in the upturned head, and it leaked straight out of #1 exhaust valve

other 3 held on a little longer

#4 held longest at about 1hour

pistons measured (with a digital caliper) in spec.
ring end gap is in spec when placed back in cylinder.
nothing to measure the internal bores with but I can see some crosshatching in there from honing.
are the bores honed from manufacture ,or would this have been done recently?
so definitely some valve issues,
but hopeing bores are ok.
stu

 

oh, and, rings were all free, motor has 47k miles
stu

 

The bores would have been honed at manufacturing. If the crosshatch is even on all cylinders then you can put all of your effort into getting the valves in order. I would go ahead and clean up the pistons (paying attention to the ring lands), and the bores with the petrolium-based solvent of your choice, just to make sure any remaining detritus dosen't contribute to premature wear. Ideally you'd remove the rings to clean the lands, but given how your rings are in good shape, and how easy it can be to break them during removal, I'd suggest leaving them in place.

 

bensalf, excellent thread and photos!
Thanks for sharing this.

 

doesn't 47K seem like a lot for still having original cross hatch?
is there a lip at the top of the cylinders?

 

So what's wrong with the exhaust valves? Can you see anything wrong?

I spent January fixing this. Not even close to an XJ, but thought you might like inspiration:

 

Both good questions. I have had, in front of my very eyes, engines with more miles that still have the original crosshatching. It's not common, but it is very possible. The main point being that there is no sign of excessive blowby at the piston shoulders, and the ring end-gaps are in spec. The cylinders could be egg shaped, but if they were I'd expect to see clear signs of blowby on the pistons. What I'm seeing appears to be leakage from the valve guide seals.

Even so, it certanly is a good idea to measure the bores while the engine is apart to confirm my assumption.

 

Rice.......I'm not seeing anything wrong with the EXHAUST valves, but that INTAKE valve looks like it might let a little too much fuel in..........unless you're figuring that with THAT condition, it's become an exhaust valve, too. LOL

The smaller ones are the intake, and the larger ones are the exhaust, iirc.......

dave f

 

-------------------------------------------------------------------------------------
The smaller ones are the intake, and the larger ones are the exhaust, iirc.......
-------------------------------------------------------------------------------------
er, no
t'other way round.
look at my pic of the head, smaller ones exhaust.
stu

 

dave

I just checked in my manual for the Seca900 and they say the head diameter of the valves is 36.1 mm for the intake and 30.0 mm for the exhaust. I would have thought the opposite.

 

take a closer look. the results of not checking and adjusting the valves at the proper intervals.


valve by bmonkey36, on Flickr

CN

 

Nice picture! No wonder the compression was very low on that cylinder!

 

Oops Well I never intended to muddy the waters with that pic, but seems I did...

First off, that pic I posted is not of an XJ. In fact, it's not even a motorcycle. It's from one of the DD's in the family. I posted the pic simply as inspiration and as an example of valve damage that can be seen with the naked eye. I had no compression on that cylinder, and after digging into it, found the reason why. I was just wondering that since bensalf's compression numbers were as gruesome as mine were, that maybe he could see something clearly wrong with his valves as well.

Hogfiddles, No, it's an exhaust valve. Burned up real good, huh? The general configuration is for exhausts to be smaller than intakes.

cyclenoob, it was a joke... Hogfiddles saw the problem. He was making a funny. Also, it's academic, but my valve problem was not caused by improper clearances and lack of maintenance. It was caused by carbon buildup on the seat that prevented proper closure. The hot gasses being pushed through the small opening ate away at the valve.

Sorry for any confusion guys... Back to your regularly scheduled investigation!

 

Dang it, got my fingers going faster than my eyes again------------didn't proof-read fast enough. Remember: more in, less out.

Yeah, I saw the problem right away-- those chunks out of the valve edges are quite something.

dave

 

Haha! "quite something" alright! I gotta tell ya that I used much much more colorful language than that when I figured out what was going on. That repair was no fun at all.

bensalf, Have you pulled any of the valves out of the head yet to get a good look at the sealing surfaces?

 

yes, pulled them all out today, took about an hour.
nothing like the damage as on "rice burners" photo, but #1 exhaust has carbon deposits on the valve and seat.

I'm trying to get some more pictures to load, but my Olympus master program has stopped working and that's where the photos are.
began clean up of the head after strip.
will try again with the photos
stu.

 

so I put photos on a stick, hope they show up

had to make a small wooden "dolly" for the spring compressor as it was too big for the head


heres the suspect #1 exhaust valve, theres carbon deposits on the seat and sealing area
but would this cause zero compression?



compared to the intake side


stu

 

nothing a little valve grinding compound can't fix

 

heres the cross hatching on the cylinders, and its fairly uniform all the way round and up the bores



stu

 

ive been trying to look for clues to tell me if this engine has been stripped before, but it all looks fairly newish , ie, no previous scratches on the mating surfaces , no rounded fasteners etc.
would the manufacturer have used silver gasket cement on the head gasket?


what other clues could there be,
the rubber "o" rings on the cylinder base and on the oil feed dowels on the block are orange, would these be oem.
stu

 

I'm no valve expert, but I don't think that carbon would result in zero compression. Lower than desired maybe, but not 0.0.

For comparison, here's what I found on my valves (the ones that WEREN'T destroyed):



And here's a corresponding seat:


But here's the trick... That motor still RAN. And up until that one valve blew chunks, it ran fine! And I got reasonable compression on the other cylinders even with all that carbon.

Maybe one of your valves was sticking in the guide? Did they fall easily out of the head, or did you have to fight with any of them?

 

they all came out easily, but I think you my have provided the answer "rice".
the pic of my exhaust valve ,above, has a carbon/rust lip on it ,probably stopping the valve from closing.
i'll have another look tomorrow.
cheers
stu

 

I think the silver you see is from the gasket it's self.

 

Well for zero compression, the list is pretty short:

A problem with the valve(s).
A problem with the piston/rings.
A problem with the timing between the two.

The valve wasn't sticking when you did the compression test though, right? You measured reasonable clearances, didn't you? It's not like you measured a tenth of an inch between the shim and the cam, right? Was there maybe some carbon chunk goober stuck between the valve and the seat that you knocked off when you pulled the valve?

Did the rings come out intact, and not in pieces? I see in one of the pics it looks like there's a ring inserted back into one of the cylinders. Are you checking ring gap there?

 

I don't see enough build-up to cause zero compression. You'd have to have quite a bit there for that, but it will definitely make a lower rate.

I'd recommend getting a 1/4" thick, or thicker, piece of glass about 8 inches long. roll the valve stem on the glass, with the valve head off to the side of the glass. What you're looking for is ANY wobble anywhere........that would indicate a bent valve.

Also ,I don't see anything to indicate a rebuild.....it all looks otherwise normal.

Dave F

 

that appears to be it "hogfiddles" at least 3 bent exhaust valves and 4th not great.
this #1 exhaust valve is supposed to be closed



after I cleaned the valve up and did a little bit of grinding
I shone a torch up the exhaust tract

 

"hogfiddles" I roled the valve stems on the base of my pedestal drill, which is a machined flat surface, 3 of the exhaust valves had a deffinate wobble,
the fourth also showed light through the exhaust tract, all intakes seem ok
so what could cause 4 exhaust valves to bend and the intakes are ok?

piston tops show no sign of impact


on another note, the camchain has a white paint mark on it, I guess that wouldn't have been on at manufacture.


maybe the chain has been changed at some point

cheers
stu

 

That is interesting news. My WAG: Perhaps there was some trouble with the cam chain or the tentioner that caused the engine to go out of time while running, causing damage to the pistons. PO honed the bores, replaced the pistons, cam chain and the intake valves, but missed the fact that the exhaust valves were bent (or simply figured, wrongly, they were still straight enough to run with).

 

so I started a search for 4 exhaust valves ,
4 oem ones would run to about £200.
I can get a complete engine for almost half that.
may try to get just a complete head.
its a 3km model number
stu

 

Woof. Well at least it seems you've found the problem.

As for how it got that way, if there's no marks on the pistons, then I'm at a loss for an explanation. At the start of this thread, you said that the bike was in your possession and running fine a couple years ago?

I might have missed it, but if it was running fine, what promoted you to pull the motor in the first place?

 

rice,

I bought this bike a couple of years ago from a salvage yard, it was a stolen recovered bike, with parts missing ,
I bought it as a project to turn it into a café racer.
I obtained the bits to get it running, and did so.
but the bike never moved, but it seemed to start and run ok.
I stripped the bike and started renovating
got the frame, wheels, forks, swing arm, calipers etc all renovated and polished, then I turned my attention to the engine ,thinking it was fine.
it wasn't until I bought a "dam" compression tester, I discovered these problems, still, better now ,than later.
I'm much too far into this bike now to let it go.
so I'm searching for 4 exhaust valves, or a complete head .
stu

 

all it takes is a little contact with the pistons to dink the valves. Being the 600, I wontder if someone was over-revving or -redlining i a lot............

dave

 

Gotcha.

I'm thinking that maybe it wasn't running as fine as you thought it was. Just like my car with the burned exhaust valve. That car seemed to be running fine with all valves carboned up. Granted, my compression wasn't as good as it should have been, but it wasn't zero like you got.

So I'm betting the motor came to you like that and the question still is how it got that way. I bet the only person who would know the answer would be the previous owner...

So, another question... You got better compression numbers when you put oil in the cylinder, right? That should not have made a big impact on the results if the problem was with the valves. Maybe you've got more than one thing going on here?

 

-------------------------------------------------------------------------------------
So, another question... You got better compression numbers when you put oil in the cylinder, right? That should not have made a big impact on the results if the problem was with the valves. Maybe you've got more than one thing going on here?

--------------------------------------------------------------------------------------
hmm. well maybe
I was wondering if putting a couple of tablespoons of acetone/atf in there, was enough to lift the compression ratio, ie, there being less volume in the cylinder when compressed? thereby boosting the numbers?

I stripped the rings off #1 piston, cleaned up the piston, and slotted it back in the bore.
then measured the piston to bore gap with feelers
the measurement I got was at the maximum limit ie .15mm ,but not all the way down the piston, i'll do some more measuring tomorrow.
I'm fairly confident with the bores/pistons being ok.
stu

 

another question, would it be possible to bend a valve whilst using a bucket holder or ziptie or whatever, when checking shim sizes.
when you think about it, you're holding the valve open whilst turning the engine to release the spring pressure, thereby raising the piston.
if the bucket holder is too long ,or ziptie, or whatever too big
could enough leverage be put on the crank to bend a valve without realising.
stu 8O

 

Not without leaving a corresponding mark on the soft aluminium piston.

 

Either I missed this earlier, or you didn't post it. If the ring end gap is at the maximum limit anywhere in the bore you need to go oversize, unless you want to tear the engine down again in the near future. If that isn't in the budget, you can go ahead and run without doing anything to the bores (again assuming that they are not egg shaped, or beyond the ring end-gap limit elswhere in the bore), and save your pennies so you can do the job properly when you start noticing excessive blowby.

 

-==============================================
Either I missed this earlier, or you didn't post it. If the ring end gap is at the maximum limit anywhere in the bore you need to go oversize
==============================================
no--no--, the ring end gap is fine and in spec,
the .15mm is the gap between the piston and the bore with the rings removed.
max gap ,in the Haynes is .15mm, but the feeler wont go all the way past the piston.
I've got loads of measuring to do to confirm the bores.
but I believe they're ok
thanks
stu :?

 

================================================
all it takes is a little contact with the pistons to dink the valves. Being the 600, I wontder if someone was over-revving or -redlining i a lot............
================================================
yeh,!! probably the cu*t who stole it
stu :x

 

Stu! Check your PM...