Checking Cylinder Compression

i'll see if i can get a hold of one of those. in the mean time & thinking ahead, what will this tell me? the decision whether it may need honed or bored would be my guess (?)

 

It'll give you the dimensions of the cylinder bore and from that you can help determine your problem.

If it needs bored, you need a new set of jugs. I don't think oversize pistons can be had for these.

 

That motor doesn't have enough miles on it for the cylinders to be severely worn out-of-taper.

I'm not seeing what I thought we would, there's no mushy pile of oily rust around the top of that one.

The "lips" you're seeing are just a carbon buildup, that's normal; like I said I don't think you've seen enough miles for there to be REAL wear.

Time to pop the jugs off. have some rags ready to wrap around the connecting rods (those things that connect the pistons to the crank, remember) so they don't get "dinged" on the edge of the engine block.

You will eventually need to make a set of wooden blocks to support the pistons for reassembly, I believe your manual should cover that. Rags will be fine for now, just as protection.

BE READY for the rings on #1 to fall out in a bunch of pieces, don't let them get down inside the motor.

 

It's nice to have a "Rubber Mallet" to help with the Cylinder Block.

An Old Sheet, ... Cut into Sections 6-Inches Wide & 4-Feet Long is useful.
As the Bottoms of the Cylinders just clear the Case exposing the Connecting Rods, ... Wrap the Sheets around all the Rods, on both sides.

Tuck linen all-in and around the Rods to PREVENT the Smallest object from entering the Inner workings of the Engine.

Buy a Piece of Pine SHELF Stock
Construct a JIG that will Support ALL-4 Pistons when they are All at the same height Mid-Stroke.

 

so off to deeper and better things I suppose.. plan remove the cylinder block soon but first I'm digging for some research & answers. this time of the year doesn't bother me in the fact that its this far apart too. not too particulary fond of riding in upper teen degree weather

thanks for the few tips already. I feel as if the connecting rod would fall apart since the piston sits on top of it. some say to construct a jig for supporting the pistons and the manual states that a second person should be present to support each piston as it leaves the cylinder. are they really that fragile? sorry for such an open ended question. this feels like I'm gonna be opening a golden egg or something though lol

I agree. the speedometer has malfuctioned numerous times but it can't have more than 20k on it. anyhow, dad says he should be able to find one of these ID micrometers at work. hope to take measurements tomorrow and get back with you fellas. thanks for your input thus far.

btw, i opened a photobucket account. a few more pictures are posted and all are much bigger in size.

photobucket link

 

Question: Do you have a factory book or a Haynes book?

Your research and answers are in the shop manual, but they tend to leave a lot of things to "pre-existing knowledge." That is, they assume you're already a somewhat accompished mechanic.

The piston is attached to the top of the con rod with something called a "wrist pin." It's a hollow finely machined pivot pin that slides into the piston horizontally, through the top of the connecting rod, and is retained by clips on either side of the piston.

Don't worry, the pistons are firmly attached to the rods by those pins (or are supposed to be anyway.)

The reason for supporting the pistons and rods is that you don't want them banging around and getting nicked by contact with the engine block; you don't want them "banging about" at all. Remember all the stuff inside the motor are precision parts; they have to be--- this is a 10K rpm motor.

The reason I asked about the manuals is I have both, (and a 650 project, which is why) so if I know which book you have I can direct you to certain sections that might help you understand what we're looking at here.

Welcome to Auto Shop 102. Read your manual, then ask away. "Pause" where you are now, until you understand the rest.

We got all winter.

 

Haynes book. I've read sections 6 through 8 so far and with your explanation below..

it clearly makes sense now. Starting to look exactly like what you've described; in sections 21 through 24 of the book. Thanks fitz

 

COOL. Study the book. ASK QUESTIONS, don't be shy about it.

Haynes books are good, there are some errors but then again there are some in the factory books. The aftermarket books for the 550s are from Clymer; bloody amateurs compared to Haynes.

I can also scan you diagrams from the factory book if the Haynes leaves anything out or is unclear.

Read up on it, go look at the motor and compare it to the diagrams, etc. Then ask questions.

Fun fact about Haynes manuals: How about a SPITFIRE book, as in WWII airplane, not POS British car? http://www.haynes.co.uk/webapp/wcs/stor ... ogId=10001

Or maybe you have an Avro Lancaster bomber: http://www.haynes.co.uk/webapp/wcs/stor ... &langId=-1

Or a P-51 mustang? http://www.haynes.co.uk/webapp/wcs/stor ... &langId=-1

Their website is amazing.

 

that cylinder wall looks pitted. unless you've got a lot of dirt in there.

2 of the pics look like a section of the wall is scratched up??? pic 11 is most noteable.

 

probably a little dirt and grime from when I was wiping the top portion off the piston with a paper towel. i felt like the jugs/chambers were in immaculate shape. any others want to chime in?

hoping that when I cautiously pull the cylinder block off by the weekend that only the piston rings on #1 need replaced. the others should be good due to the compression strength they provided hopefully *fingers crossed*

 

Do all the pistons at the same time, then you know they are all good and you won't need to go back in again for a while.

 

yep, if you only do one piston. your still going to have 3 weeker pistons.

do all 4 pistons and you'll have much higher compression all the way.

 

boy oh boy guys, this is getting pricy for the shape my wallet is. 5th year engineering student at a private college, about to graduate in may finally.

questions about quantity then. started getting a menu put together for analysis. per chacal's catalog...

however, found these on ebay for a significantly lower price. ebay piston rings am I missing something. grant it, the ones on ebay are for a +1 boresize but why such a huge price difference?

 

Go buy a few cheap Bottles of Rubbing Alcohol.


Level the Pistons at Half-stroke: ➙ ䷉䷉䷉䷉
Pour 2 Oz of Alcohol in each Cylinder.
See how long it takes for the Alcohol to drain past the Rings.
If Number-1 is way faster than 2, 3 & 4 ... expect fragments.

Level the Head with the Combustion Chambers UP. >> LEVEL ⌣ ⌣ ⌣ ⌣
Spark Plugs IN
Fill each Combustion Chamber to the brim with Alcohol.

You want to see NO Bubbles
You want to see None draining out.
If you have a leak, ... you need to Lap the Valves.

 

Sure, one set will do the job, but the other three have been doing just as much work as the one that's broke. Take into consideration your time so far, a new set of gaskets and all the other stuff you've invested in. It may run for years with the one repair, then again two weeks after you may have to tear it all down again, new rings, gaskets etc.
You have come to that point in the rebuilding phase where you put off doing the job right til you have the extra cash or doing a partial repair and getting religious real quick!
I'm surprised that you haven't found something else that needs fixing now that you are that far into the rebuild.
Good luck with whatever you choose to do, but to be honest, it's still winter here (in London Ontario) so unless you can go riding as soon as it's all buttoned up, I'd hold off until you can get all four.

 

this would be good if the fragments don't drain down into the engine wouldn't it? seems counterproductive to drain a fluid into the engine that would flush more particles into the engine, unless this wouldn't be such as big as a problem as I think it would... just wonderin

 

The oversize rings are likely cheaper because you can't find the oversize pistons to wrap them around. They could also be of a lesser quality.

 

At this point, I wouldn't bother. We already know there's a problem with that cylinder; the jugs are going to come off, so I agree that let's not make any more work.

Rick's other advice about "stuffing" the area with an old sheet, cutting out a plywood "deck" to support all the pistons, etc; is all very good. I don't think we need to do a "leakdown" test at this point.

I would hold off ordering any parts until the triage process is complete.

 

alright, got up early (7:30 is early for me during a christmas winter break lol) to remove the cylinder block. it seems very stiff and I'm afraid of rocking it since the pistons are in there too. just lift straight up right? i've got a gap so far by tapping with rubber mallet about .25"

the only nut i removed was in the front and it wasn't as big as you were saying fitz; 12 mm so maybe i'm not seeing something else?

 

Just lift straight up; is the rear chain guide at least loose so it's not snagging?

And this is where you need the second set of hands to "catch" the piston/rod assemblies as you pull the cylinders free, and wrap a rag around them.

 

got it off. by myself. feel like a champ. pictures to come very soon. piston number 1 is not bad at all. rings look new. pictures will be up soon

 

okay, pictures are on the photobucket link piston examination. pictures show the #1 piston closest and i took one other picture with flash towards down the cam chain gap just to see what's down there. i really think the rings are good. i can rotate them fully on the piston and there is no cracks or missing pieces from what i could tell. gonna wrap the rods now so i can make sure the pistons are stable.

tell me what else you fellas would like to see and i'll snap them

 

And they (the rings) aren't in pieces?

Something is weird.

Check something: Gently grasp each piston, and try to move it in relation to its connecting rod.

It should move ("slide," kinda) purely horizontally (on its pin) from side-to-side, a small distance.

You should NOT be able to "rock" it side-to-side at all (front to back, yes, it rotates on the pin.)

Pull straight UP on each, ensure there is no "up and down" play.

Compare how the other three "feel" in relation to their connecting rods, and compare to #1.

I'm concerned about the overall condition of the #1 piston; I'm wondering if it's cracked underneath where it supports the wristpin, or something else is up.

Check the #1 rod; perform pretty much the same tests on it: it should slide slightly side-to-side on its crank journal but have NO PLAY in any other direction (no "rocking," no up-down play) other than purely rotational fore-and-aft, as it rotates around its crank journal.

And let's see some close-ups of the #1 piston, rings, etc.

I'm currently stumped; until we can see more, anyway.

 

Your photobucket link takes me to the main page not your gallery.

 

This is his album: http://s1115.photobucket.com/albums/k549/moellear/ link is back a page.

I've never been this deep into a XJ motor but based on other engines I have rebuilt that top ring gap on #1 looks pretty large. I'm wondering if that's big enough to cause the issues. Or maybe I'm not seeing it correctly in the picture.

 

yeah sorry about that previous link. thanks to iwingameover for the link. the four pictures I quickly snapped are generic of the entire thing. after lunch i'll snap some very descriptive pictures of #1 and one other to compare.

i'm stumped to this point too. in a way it feels like a waste of time for this total break down, especially if the rings aren't in that bad of shape. oh well, i can definitely say i understand the crankshaft and piston movement in any engine now.

 

You may want to wait for someone else to chime in....

but the next thing I'd do is take those rings off the #1 piston and check their end gap. You do that by putting the ring into the bore of the jug and measuring with your feeler gauge what the space between the ends is.

Make sure the ring is level across.

I don't know what the spec is for these.

 

No, there's something going on or you wouldn't have been getting really low numbers dry and really high wet. I'm worried about the #1 piston and rod themselves at this point; there has to be a reason for getting those readings; and they kept being repeated. Something is amiss.

Do the "wiggle tests" I outlined and report back...

 

With the gap shown in this picture 1 the gap looks a little too open (I know it will compress a bit when it's inside the cylinder) and 2 shouldn't the gaps be at like 90 degrees from each other? If the gaps are lined up like that I'm sure that it would affect the compression, unless you have moved them since lifting off the barrels.

 

He has moved them around.

However, I agree 110%; next step would be to check the ring end gaps.

I'm developing a theory:

Look closely at the cylinder walls in hole #1. There are "stutter" marks up near the top; this generally indicates a partial seize condition.

I'm leaning toward: At some point, the motor seized up, or nearly so, in #1. A PO re-ringed JUST THAT cylinder, and didn't do it right, didn't hone it, and/or didn't understand about ring end gaps, or even used the wrong parts. Those rings look awfully new compared to the piston itself...

The validity of this theory will hinge upon: The results of the "tugging and rocking" tests;

and just exactly what the ring gaps are, compared to spec. They look scary-wide to me too.

I'm still concerned about the overall condition of the #1 piston and rod. But let's don't pull the piston off the rod just yet, let's see what the ring gaps tell us, and see if there is any "improper" play in that piston/rod relationship anywhere.

moellar I believe your book covers how to check ring end gaps, ask questions if you don't understand.

Input, anyone?

 

Also, IIRC the rings also have a "this side up" application don't they? So if the rings are in the wrong way that would drastically affect the compression. Not sure about this model but I think there is a slight chamfer (SP) that should face up I believe, if the chamfer was down it would allow blowby by allowing the rings to compress into the grooves under compression. Been a while since I've done this kinda thing, so just throwing it out there.
\_| = correct
_
/ | = incorrect
Crude, but I think you get the idea.......or not. LOL!!!!!

 

You may be right about the chamfer but it's too late for that now.

Maybe a piece of ring broke off, making the gap that large, and is long since missing?

 

may seem like an interview but i've thoroughly checked over things. at the end I'll come up with something. others feel free to chime in. I've put a lot of time and exhaustion getting this far. want to come up with something. going to have dad take a look over things when he gets home, with an ID micrometer tool to measure the jugs. should i look at anything for the jugs or the head itself??

nope

yep. slides horizontally about 1/8" more or less. all 4 do so evenly.

All four are have evenly distributed strength connected to the connecting rods, which in response do not lift up off the crankshaft at all. no hesitation about that

I checked underneath and also tried to get a snapshot of the underside when the piston was at TDC. I didn't notice anything and all lubrication was smooth on all four of 'em.

on my photobucket again. hopefully this is the correct link. piston examination

So what can I think of? not much considering the amount of mechanical background I have. the only thing that I can propose is maybe a ring got just enough resistance against the jug wall to have lower compression. however, why would the compression increase dramatically beyond the excessible amount others say >175psi consistently? this really puzzles me


side note: since the head is off, I'm currently changing rubber on the tachometer drive unit, *perfect timing to visually see everything * the bolt in the housing unit is STUCK :evil: i've ordered kroil but in the mean time tried heat & other lubrications but its not budging. even used steel plate rather than screwdriver, and the plate gets twisted every time

 

Here's my theory. it follows along with Fitz's.....

Those rings were setup incorrectly, the gap is too wide.

You want the rings tight against the cylinder wall or no compression. That opening in the ring has to close almost completely when in the cylinder.

Next step is to check those ring end gaps and might as well measure the bore.

The oil (wet test) increases the compression for two reasons:

1. it seals (temporarily) the bad rings.
2. depending on who much you put in it takes up volume. Less volume above the piston = higher compression.

 

okay i like the idea iwingameover and fitz. however, if the gap in the ring didn't completely close then how did the oil not drain. i agree less volume above the piston = higher compression but if the gap wasn't fully closed then wouldn't the oil just run down the side wall where a slight gap would be present? (maybe too much of a question to get an accurate answer but I'm used to asking nitty gritty questions in engineering courses)

gonna take some precise measurements either this afternoon or tomorrow. gotta busy night ahead of me. there's gotta be something wrong with the rings... or else I would've never gotten an increase in pressure in the first place.

 

The oil would have leaked out..... eventually.

The gap does not have to be very big to allow pressurized air to escape. The oil was under no real pressure until the motor was spun over and obviously filled the gaps..

Example: take a balloon, blow it up and tie the end. Now poke it with a small pin. Bang, no more balloon, all the air pressure released qucikly.

Now fill a similar balloon with water or oil and poke it with the same pin. The water or oil runs out in a nice smooth stream until it's empty.

Your compression loss works the same way.

 

Good analogy. Also, because the gaps are NOT aligned when the piston is correctly installed, the resultant overlap would trap the oil.

The "ring gap test" results are going to be the biggie.

moellear Your book shows you how to measure the bores; I'm not expecting to find a lot of taper, but it won't hurt to check them. Your book gives "taper tolerance" specs, I believe. If not I can look them up in the factory book.

Other than that you're looking for scoring or pitting; I'm not seeing any.

Re: tach drive unit: You found this already, right? http://xjbikes.com/Forums/viewtopic/t=19538.html All I can say beyond what's in the how-to is KROIL and gentle application of heat. I actually did two of them for the article, one came right apart and one put up a heck of a fight.

 

Here's my Sherlock Holmes.
The bike was ridden in-town with questionable oil quality and increasingly colder weather, causing incomplete combustion and no residue burn-off.
The ring that was crud-fouled was actually de-fouled by the wet test.
Some PB-Blaster, good oil change and 75 MPH riding would have cleaned things up. I'm saying there's nothing wrong with this engine.

And - rings rotate as the engine runs. The top ring rotates one way; the bottom the other. Except for 2 strokes.
Whatever careful ring alignment you do is lost in 10 minutes of running.
(Best of luck Moeller)

 

I disagree. Look closely at the #1 cylinder. That had a piston seize, or try to seize in it, although it doesn't appear it was real recent.

There is something truly wrong with this motor; it's just not super obvious (yet.) This is becoming "forensic mechanics."

Quite frankly, I'm beginning to suspect a PO may have replaced the #1 piston/rings without any fitting or honing, after it seized up on him. Might even have had a holed piston.

Let's see what he gets for ring gaps. They look insanely wide to me.

We also need to get that piston measured; it might not be in spec anymore from overheating. But first things first.

I want to know what the ring gaps look like.

 

I've been following this thread with interest, sure beats "how long should my kickstand be" threads.

Moellear, no matter what, this engine needed a top end rebuild so don't for a second feel that you've wasted your time. I took the time to review each photo that you took and other then not have a couple good, bright pics of the undersides of the piston crowns, you did a great job of posting pics.
To me, #3, #33 and #'s34&37 tell the story. This engine did indeed suffer a sieze or partial sieze as fitz noted. It's illustrated in # 34. Remembering the siezures typically occur at the top of the stroke, when the piston heat is it's highest. #33 shows what appears to be scrapes along the cylinder walls. The biggest indicator is #3. Look at the space between the top ring and the top edge of the piston.....where all the other 3 pistons have a nice, even coat of blowby, #3 shows direct cylinder wall contact. Also noting that there are little to no hone marks. Guys, I have an H2 engine with 15000 original miles and when I pulled the cylinders to mod them, the original hone marks were clear as day, and that's a high performance 2 stroke engine!
Yup, I think #1 (along with the rest of the engine)was run without(or very little) oil then the owner, attempting to compensate ran it with a crank full of STP or other oil thickening agent causing all that cooked gook that we can see throughout

I'm not going to offer any suggestions because I don't want to send you off to chase your tail. I think that you're in good hands now with Fitz and just go through it methodically and step by step and these guys won't steer you wrong. As far as the rings go, when you pull them off, look for any marks, they are always supposed to be installed, marks up! I have a feeling you'll find the top ring very, very loose and the test oil got between the piston and ring then the compression forced the ring against the cylinder harder then normal, causing the super high readings.

I truly wish you the best of luck with this....and I'm confidant that you'll get it sorted out.
Jeff

 

I would a one Ring and use at as a Measuring Device to determine the Inside Diameters of all four Holes.
Set the Ring at the SAME Depth on all four Holes.
Measure the Ring Gap and note any changes.

Something looks strange about those Rings on the No.-1 Piston.
Carefully remove the Compression Ring and Wiper.
See if there is a [ Dot ] or a "Top" or "Up" marking on the Ring.
They look Up-side/Down.

The excessive amount of Blow-by looking wear on the 1-Piston Crown makes me think that you're going to be OK after you Hone the Holes, ...
And ...
Measure the Holes to see if you need STD or OVERSIZE Rings.

 

Rick, is there a proper way to remove the ring? I've read the manual but didn't come across anything on what to use to take the ring off. little apprehensive to just use my fingers. last thing I'd hate to see it bends or snaps :cry:

i agree. maybe the rings are just upside down. maybe the rings are slightly bigger than spec allowing some air to swiftly pass by giving me low compression. its a shame I didn't do any of this compression testing 2 years ago when I purchased the bike.

of course at that time I was just learning how to drive. i'm lucky nothing major has gone wrong thus far and hope this rebuild does me good once said and done. i really appreciate you guys taking the time to inspect something for me by pictures and coming up with theories. it helps everyone out, especially me with a problem that I really discovered out of no where.

 

if the rings are upside down. you've driven it for 2 years. i wouldn't attempt to reuse them.

i wouldn't attempt to reuse them if they were only ran for 5 seconds.
they were installed wrong. and they were put to use.

buy new rings.

check the jug. if it needs honing. you can probably buy the standard rings. along with some expansion material. the material goes inside hte piston groove and the ring goes over that. the expansion material helps to push the rings into the cylinder walls. your basically taking up the slack from losing a little meat from honing the cylinder wall.

there is a piston ring tool that is used to take the rings out. it basically spreads the rings enough to slide over the piston. although you could probably figure out some other way. they have to be spread wider then needed to break. you just want to spread them enough to slide off.

 

Take a few Feeler Gauges and slip them between the Ring and the Piston.
Keep the Ring from having any torsional force applied to it.
Move it off toward the top keeping it leveled or it will snap in half.

 

This is a piston ring expander, you may be able to go to a local auto store and see if they have a "Loan a tool" program.
Oh, and if you're not sure how to use it, ask the guy at the counter. It's pretty self aexplanitory, but spread the ring just enought that it will slip up and over the piston. Like the other guys said you should probably replace them anyway.

 

in the automobile engine when you put the ring inside the cylinder and check for end gap. i think the spec. is .005 inches.

the rings were put to use. so now they are worn down to fit the position they were installed. putting them in the right position will be no good as they are worn out and no good anymore.

 

The REAL specs are:

0.0059 to 0.0138 (inch)

 

for what? cause I'm getting .300" +/- for all eight ring gaps. will post description of what i've measured so far soon

 

sorry TIME. didn't read snowwys post

 

okay did i do this wrong?? three snapshots are up on my photobucket link of what i measured. ring gap measurements

measured all four pistons; both compression and wiper rings

#1: what we're really concerned about,
top ring = .302"
wiper ring=.311"

#2:
top ring= .300"
wiper ring = .311"

#3:
top ring=.295"
wiper ring=.297"

#4:
top ring=.290"
wiper ring=.312"

as far as consistency, all four seem to be really close. these measurements were done with a manual caliper. the book states on pg 71 "Piston Ring End Gap installed"
Top and 2nd = .0059-.0318"
Service Limit= .0394"

therefore I conclude a.) I misread the caliper or b.) the gaps are ALL too large.

just double checkin; these measurements are taken on the ring when the rings are not compressed correct? obviously if you push the rings together like the cylinder jugs would then the gap would come so close together they should almost close right?

i will have measurements for cylinder wall/jugs taper either tonight or tomorrow