Checking Cylinder Compression

Hey -

how about removing a ring from the piston, and inserting it into the bore 1/2 inch down from the top, then use feeler gauges in the gap??

The ring has to be "square in the bore" usually accomplished by pushing down with the piston, but you could use a drinking glass or soup can. And scroll-up to Maxim-X's post, and buy/rent that tool - - you absolutely need it or you will damage your rings, and, don't flip your rings - keep them right side up AND in order (100% organized).

 

Time's right.

Those measurements you took are not critacal. They only exist in the condition the motor is in now.

The specs he notes are for the ring, compressed by the bore in the cylinder, then you measure the resulting gap with a feeler gauge and it should be within the specs noted.

This is what we need you to do: http://www.muller.net/sonny/crx/rings/index.html

Use Time's specs but the process is the same.

 

the gap is checked with the ring in the cylinder. not sitting on the piston.

you don't care how it sits on the piston. you want to know what it's doing when it's installed.

that's what i meant, time. added one to many zeros. wasn't sure about the .01 though. but i thought it was in that ball park.

 

sorry guys. shoulda gave it some thought. oh well, learnin experience thats for sure. anyhow, was able to get one compression ring off (#1) with two feeler guages and placed in jug/cylinder. see pics of it on photobucket again :lol: ring gap measurement #1

the guage reading i got was .023" or .584mm which looks to be within spec for the book. however, not in TIME's spec

 

I'd do one of the others from a different piston in the bore it goes in.

Your measurement seems large for a ring end gap. And based on Time's spec you're 0.0092 over the high range. The range is only 0.0079 so you're twice as wide as the allowable gap.

Which for this purpuse is a big deal.

Measure another ring in another hole and you should see the difference.

 

Don't get too far ahead of yourself.

You need to Rent a Hone.
Then you'll have to Hone and De-glaze the Cylinder Walls.
Once you have the Cylinder's prepared for Measuring; do the Ring Gap Test.

The Ring Gap Test will determine if you are OK using STANDARD Rings or need to Fit Rings that are OVERSIZED.
Much will depend on how well the Bike was serviced.

You may find that the Ring Gap is too WIDE for STD Rings AND Too Close for the First Oversize.
In that Case you will have to CUSTOMIZE a Set of Ring for EACH Hole by carefully removing Material from the Ends of the Ring with a File or a DREMEL Tool.

 

Rick, that would be his end goal.

Currently I think we're still trying to sort out the original issue. Comparative measurements to another cylinder would show if the rings on #1 are drastically different than the others or the main issue is somewhere else.

 

harborfreight sells the hone tool. or did he say he was too far.

 

Now you're getting there.

Don't worry about comparing to specs just yet; let's check the gap on all of the rings from #1, in the cylinder about 1/3 of the way down, and post those. You need to be sure the rings are sitting squarely in the cylinder, measure down from the top if you need to.

Before you pull the rest of the rings off #1, check their gap in their respective grooves; there's a spec for that too.

Then take one and check its gap in the other cylinders.

Also, carefully inspect them as you remove them, it would be nice to confirm whether or not they were installed upside down.

Did you have a chance to put the ID micrometer in the bores yet and check bore and taper?

The other thing that we're going to want to do is to measure that #1 piston's diameter and see if the piston itself is in spec. You can do that after you strip its rings. If you don't have a big enough/precise enough caliper to measure the piston, take it to an auto parts store or "real" auto repair shop and ask nice.

I'm also leaning toward having you pop the circlips and pull that #1 piston off so we can have a good close look at the underside too. But let's not get ahead of ourselves just yet.

*TIP* You can use 3 or 4 inch-and-a-half wide strips cut vertically from a 2-liter soda bottle instead of feeler gauges to slide the rings off the piston with; just be sure one is under the ring's ends.

We'll get to the honing/refinishing/repair and reassembly stage once we know what the heck is up in this motor.

 

Oh, and one of these to clean the carbon out of the piston grooves

Your barrells should look like this after honing


using a tool like this (example)


then get a ring compressor (example) and an extra pair of hands as you will be putting the barrels back on from the top

Hope all this stuff isn't scaring the sh*t outta ya.

 

You can Rent a Hone like the one shown here at AutoZone, RentAll or the Rental Tools department in some Hardware Stores.



The Spring adjusts the Force of the Hones on the Cylinder.
Heavy force isn't needed.

If you have the Block on a Bench and are Honing the Cylinders Horizontally; take GREAT care NOT to let the Hone Elements be inserted too deep in the Cylinder that they escape.

 

you can use an electric drill to run the honer through the cylinders.


you want it at a somewhat slower speed then using it as a drill though. but not slow enough that it just creeps along. and move it up and down as she spins. so you get the cross pattern like in the picture.

youir going to need 4 of those ring compressors as all 4 cylinders will be going in at the same time. or 2 from top center and the other 2 from bottom center. (something to that effect)

 

All very good advice.

For when the motor is going back together. Right now we're in diagnosis mode; examination of the #1 piston and cylinder hasn't been completed yet.

 

Am I the only dino out here that still hones by hand? I have a nice 3 stone hone but just prefer to do it by hand.....

jeff
sry, didn't mean to hijack the thread...

 

I apologize for the slight delay. between working part-time at arby's and visiting family (since it is my christmas break afterall), I've come to a slight halt. also, many thanks to those with advice on honing the jugs/cyclinder walls. at this point I am still digesting the specs and trying to figure at what the problem was :?

so i took some time this late morning and got some measurements. the taper in the cylinder jugs is present but nothing major wrong from what I perceive... the ID #'s are measured (to an average) about 3/4" (measured to be sure they're level) from top & as well as bottom.

#1: top=2.478"
bottom=2.481"
#2: top=2.477"
bottom=2.481"
#3: top=2.480"
bottom=2.480"
#4: top=2.479"
bottom=2.482"

also, got the correct ring end gap measurements for piston #1:
compression ring=.022"
wiper ring=.014"

#2 compression ring=.017"
#3 compression ring=.016"
#4 compression ring=.019"

Before I put the rings back on #1, took diameter reading of Piston #1 and got 2.463" which makes sense, since it should be smaller than the jug/cylinder wall ID :lol:

Then reinstalled rings back on #1 to get the ring groove clearance. boy, those were tight (which should be good correct?) and for the top compression ring, only got .002" and couldn't even get a clearance for the wiper (second) ring.

no, you wouldn't be the first. I just don't have the proper tools but wouldn't mind trying. alternatively is it cheaper? this would be the only thing I'd see myself honing so it may just be better to have the shop do it

btw: i couldn't find the ring gap remover tool (looks like funky pliers) at any automotive store in town. autozone, advance auto, or napa said they should be in stock on shelves but couldn't even get the employees to find 'em for me. so i just did it like i said before.. 2 sets of feeler guages 8)

long story short, what can you guys suggest my next step be?

 

your top end number should be HIGHER then the bottom number. not LOWER. it gets the most heat so it should wear down more.

all 4 of y our rings end gaps are beyond max specs. .0059in - .0138in
.15-.35mm

you took a reading of #1 cylinder ID at the very top. what's the other 3?
standard bore size is 2.4803in. limit is 2.4843in.
taper limit is .0020in .05mm
ovality limit .0004in. .01mm
piston to bore clearance .0012-.0020in .03-.05mm

AND FOR THE LAST QUESTION. did you pay attention to the rings so we would know if they were installed wrong???

youi'll probably be allright with just honing all 4 cylinders. put new rings on it. including the bottom oiler rings. put some expansion material in there also. your going to want to take up the slack you've just gained from honing the cy linders. once them cylinders are honed. you should have pretty close to same measurement from top to bottom.

a honed cylinder will always be a little wider then stock cylinder. but honing is much better then boring the cylinder. boring takes out more material. leaving your cylinder THINNNER. and more prone to heating issues.

i've seen lots of cars bore there engines out to the max. and they can't stop them from overheating in the middle of winter.

 

Hold on - -
I gave the installed spec RANGE, not the LIMIT.

PISTON RINGS END GAP INSTALLED: (top and second)
0.0059 - 0.0138 inch
SERVICE LIMIT - 0.0394
(oil wiper rings)
0.0118 - 0.035
SERVICE LIMIT - 0.0591

PISTON RING GROOVE CLEARANCE:
top - 0.0012 - 0.0028
LIMIT - 0.0059
Second - 0.0008 - 0.0024
LIMIT - 0.0059
oil wiper - no specs (from Haynes Service Manual)

---------------------------
So, we can conclude that the rings are in-spec and begin the clean-up process?? Get the Easy Off and ScotchBrite pads and have at it!!

 

beats me. i figure specs are specs and since all four over the range but under the service limit, what's right and what's wrong? leaves me clueless and wondering how much of a change would benefit me if i purchase all new rings.

first of all, NO i didn't. were you there? and didn't you read what i described?

sorry to sound bitter but read. I try to be as descriptive as I can so there's no confusion. afterall, i was the only guy measuring

wouldn't that defeat the purpose of honing? what kind of expansion material would work? if these pistons rise and fall thousands of time per minute, i wouldn't think any material besides oil lubricating steel would work especially with such a tight tolerance.

i carefully looked at all four compression (top) rings and did not find a stamp or any notification on which is the correct top/bottom. i cant tell by the shape of them anyhow since they've been in operation for at least two years, since i've owned the bike. as a result i personally can't tell if they were installed correctly or not, given my mechanical experience on the guts of an engine btw, i've kept them all the same orientation as they were on the bike so worries there lol. any other way i could maybe find out?

 

when you hone the cylinders you lose some meat. when you bore the cylinders you lose qu ite a bit of meat.

when you hone the cy linders. you should have even readings from top to bottom. since you lose some meat trying to make the cylinders perfect again. you use expansion material. it acts like a space to force the rings into the cylinders tighter. your cylinders are no longer stock diameter. but if you want to replace the cylinders. then you won't need the expansion material. you will have stock diameter.

the rings themselves are shaped in a manner so what when installed. they indicate the correct way to be installed. OR, they are scribed with a marking to indicate which way is top.

make sure you measure the skirts of the piston. (very bottom end of piston). the skirts are what hold the piston solid in the cylinder. if the diameter of the skirt is less then the diameter of the crown (top) of the piston. the piston will rock in the cylinder. you will have piston slap. it will sound like the motor is pinging due to low grade quality fuel. only it will sound worse.

I READ YOUR POSTS JUST FINE. you measured all 4 cylinders and posted all 4 measurements but only posted ONE measurement of the top of one cylinder. the portion that gets no wear and tear.

i would never use rings that are beyond max specs. but not close to serviceable limits.

i also read your post where you claim the ring end gap is within spec. you measure .023. that is within service limits but beyond spec of .0138.

the rings are useable but i wouldn't want to have to tear down the motor again in the future if something went wrong.

tear it down once. do the job right. and do it one time only. nobody likes to do a job twice.

 

somehow these #'s don't sound right
.15 to .35 service limit at 1 !!!!
but the inch #'s
.0059 to .0318 service limit .0394, make more sense
this wouldn't be the first time the books been wrong
carry on gentlemen

 

If you measure the ring gap with the ring at the top 1/4 inch zone, then slide down to the top wear zone, measure, subtract the top #, divide by PI (3.14) you end up with an accurate measurement of cylinder wear without using inside calipers.

Polock - I had to correct one of Haynes' numbers. A typo in the book.

Snowwy - where can I buy some of this Expansion Material - can you post up a link?? Further reading?? Free samples??

 

i see what you did, convert .35mm to inch .0138 with a service limit at 1
that makes a upper limit to service limit of .0256
but
if the .35mm is the typo and .0318 is right then the difference from the upper limit to the service limit is .0076
my .02$ thinks the .35mm is wrong and .0318 is right

 

PISTON RING GROOVE CLEARANCE:
top - 0.0012 - 0.0028
LIMIT - 0.0059
Second - 0.0008 - 0.0024
LIMIT - 0.0059

-----------------------

I didn't convert the figures, but the Second Ring clearance was wrong -
Haynes Manual said:
"Second - 0.008 - 0.0024"
I just added a zero so it would make more sense. It's alot of zeros !!

If somebody would like to double-check these specs from the Yamaha Service Manual, that would be a good thing.
(edit/added, .0318 is Moellear's typo from earlier)

 

eight thousanths of an inch... the smallest feeler gauge i have is .002" so like i said, couldn't even measure the ring clearance to groove. no biggie. must be good enough for specs. thanks for the clear-up though TIME and Polock

so i seen Fitz's write up this morning on head gaskets. i just recently purchased these (aftermarket) and thought i could just place the new ones in place. never gave it a thought the old ones were still in there. after careful inspection, i found more evidence leading to my #1 cylinder problem.

take a look at my photobucket. link pictures are worth a thousand words. lol #1 valve is oily and gummy in there. the carbon build up at the exit of head; near the header gasket I was gonna replace just a minute ago. is this an acceptable amount of carbon? go ahead and clean any crap I can get to with my hands? notice the other three valves i could see with my "head"lights (I use when camping) are clean and barely any trace of oil is present. should I be getting myself into more work now... a valve job/inspection?

btw: many thanks to Fitz for the head to header gasket write up. I put the new aftermarket gaskets away cause I couldn't get them to snug with the header & bolts. shoulda known the old ones were still in place. duh. should be able to get the job done correctly soon

 

y our poor compression is related to improper seating of the rings. that also cause engine blowby. you were sucking an excessive amount of oil through the rings. your air filter box(if it still exists) is also probably covered with oil where the crankcase breather hooks to the air box.

i've never personally bought expansion material. but i beleive it can be purchased from anyone that sells engine rebuild kits. (auto parts stores, engine rebuild shops)

it should be a common place material as most engine rebuilds usually get just a hone job. but how commonly used it is i couldn't say.

 

so my piston ring end gaps varied slightly from #1 to the remaining three, concerning the top compression rings. could the small difference of .022" with #1 compared to .016" or .019" or .017" make such a dramatic increase in compression? seems like a long stretch to me..

and nobody else has anything to say about the carbon build up at the exhaust ports? guess snowwy66 must've got it right on.

i don't plan to use any expansion material though.. has anybody here?

 

I haven't had time to compare your findings to the (factory) manual yet; the oil in the exhaust port could be from the wet tests or could indicate a valve stem seal "in need" which is OK, those need to be in the reassembly game plan anyway. But that's a ways off, we'll discuss later.

Ixnay on the "expansion material" we will be able to do this right, no worries.

I'll try to dig into the factory book tonight and like I said, that will produce a couple more questions from me.

 

if he hones the cylinders. he has .003 inches of taper. he's going to lose AT LEASE .003 inches of cylinder meat to make the jug nice and even again.

that's .003 inches of piston to cylinder clearance he's going to gain. or higher.

the piston rings also won't seal as good. he's also going to have that much more looser fitting pistons. but that situation would be remedied by knurling the piston skirts.

wonder how much and how hard new jugs would be to install. then he's got the stock size. and not have to worry about taking up the extra slack.

 

how many miles on this engine?
now the big question, do you really love this bike and want to keep it another 5 years?

 

18000 +/- miles. the speedometer used to work intermittently (problem solved since this past summer) and was not working for PO two years ago. young engine life in my opinion for yamaha, which adds to the confusion

yes. this bike is my starter bike and I would like to keep it for a few more years at least

 

since you've got the piston out. make sure to measure the outer diameter at the very bottom of the skirt. (lowest ends). and measure the top of the diameter.

the bottom number should be higher or even with the top number. the piston skirt keeps the piston snug and not dancing around. if it's less. then the piston has a chance of dancing around and causing piston slap.

the piston skirt can be knirled if need be to make the bottom slightly larger then the top.


((this dude joins the internet. and he gets all kindsa free schooling on building an engine))

 

No knurling. If the piston's become "tapered" or distorted, it gets replaced; this ain't a Ford V-8.

I finally found my 650 book(s) and spent this morning's "quiet time" comparing the factory and Haynes manuals in regard to this subject.

Oh golly.

I highly recommend anyone tearing a 650/750 down this far have a factory book, the Haynes is just flat MISSING a lot of important info and details.

Now, some questions:

Where on the piston did you measure its diameter? Factory book says measure it at a point 7.5mm (0.3") up from the bottom and place your micrometer at a right-angle to the piston pin. Get that measurement and post the result if you would.

Is the top of the piston clean enough to be able to see any markings and the little arrow on top?

Are there ANY markings/numbers, anything, on either side of the top two piston rings? (anything that's there should be on the "top" of the ring, but that assumes they were in there correctly to begin with.)

Where in the cylinder did you put the rings to measure gap? Yamaha wants you to do it at the bottom of the stroke. If you didn't before, get us some gap measurements from the top two rings at the bottom of the stroke.

Were you able to get "side clearance" measurements? (The gap between the rings themselves and their grooves in the piston.)

And last but not least, PM me with your email address so I can get you some pages from the factory book, to fill the HOLES left by the Haynes.

 

originally it was measured where the grooves are. re-measured this morning perpendicular to the piston pin where the factory book says and got 2.479"

yes, arrow is present and also a raised circle at the center of the piston. see pics on photobucket link

also when handling the rings this morning, i held 'em up to the window and daylight helped me spot an "F" (without the parenthesis) on all top rings at same location and an "R" on top of the 2nd wiper ring. what would these mean? what else have other guys seen on the rings to notify up or down? i'm guessin Forward & Return for mine...

originally took end gaps with ring in cylinder about 3/4" from top. took measurements with rings at the bottom of STROKE, or where piston reaches its minimum point approximately 1.4" from VERY bottom of jugs, this morning and here's what i got
#1: top ring- .023"
2nd ring- .016"
#2: top ring- .019"
#3: top ring- .018"
#4: top ring-. 019"

I was able to get a side clearance of .002" between the top ring itself and the groove on piston #1. Did not even get a feeler gauge between 2nd ring and groove though. too tight

PM sent. thanks

 

EXCELLENT.

Now let's run these against the factory book and see where we're at.

I'm becoming highly suspicious of the piston itself; stay tuned.

The marks being on top means the rings were assembled to the piston in the correct orientation is all.

I'll post back in a few hours; I'm at work, 56 miles from home, and it's about to start snowing big time.

 

Just a note, or question - -
Is the XJ piston diameter above the top ring sized smaller, on purpose, or is it made the same size as the skirt??
I'm only asking because automotive pistons are made with some clearance there for the inevitable ridge that forms.

 

Honestly, I don't know. The only way to truly tell would be to "mic" a brand new one; If they are, I would imagine it's only by a few thou.

The only "published" spec is for the measurement of the skirt as I described.

Good question.

 

Time, I havn't noticed any difference in diameter.

 

Ok, was that with the piston as is or with the ring grooves cleaned out?
Just curious in case there is a build up inside the grooves.

 

is it possible to have rings too thin in diameter?

cuz other then his compression being non existent. his cylinder sounds like it had no reason to be dead.

didn't see any measurement of what his piston skirt is in comparison to the top of the piston though.

how about a magnifying glass and checking the top of the piston for any cracks.

maybe the rings were made in some other country and just didn't last at all.

 

It would be POSSIBLE, ... But, I think "Very unlikely" to have BOTH, the WRONG Rings AND the wrong Rings placed Up-side/down.

But the Grooves in the Piston would have taken a tremendous beating from Rings with the wrong THICKNESS having been installed.

Because there is a premature loss of Compression ... "Across the Board" ... at this point we should be verifying the correct specifications of EVERYTHING there is to get a specifications measurement on.

I-D's. O-D's, Round, Part Numbers, and the Possibility that Engine might have a set of Incorrect Pistons and Rings.

Have you looked-over that No.-1 Piston with a Magnifying Glass for a Hairline Crack or a Fracture that is getting started?

 

We're in the process of exactly that, Rick; comparing the measurements, done Yamaha factory-style, to the specs in the factory book.

The other three cylinders were fine, good compression and no issues. But #1, no such thing. I'm beginning to suspect that JUST THAT cylinder had an unfitted, salvage piston thrown in it at some point.

If you closely at the pics (have to follow the links to photobucket,) the cylinder walls in only that cylinder show some "stutter" marks toward the top, an indication of a seize or partial seize.

I'm betting something horrible happened in that one pot, maybe it even holed a piston; and somebody just threw something in there.

 

i've never taken a bike motor apart. are those piston pins pressed in. or do they have c-clips. cuz that would be a lot of work and money to just throw something in to be able to ride. i'd rather buy another $500 bike.

somehow i just don't see any joe wanting to just throw a piston in.

 

The XJ's pistons use circlips.

SOMETHING scuffed the upper walls of that cylinder; and I don't think it was that piston.

Sherlock Holmes says that when you eliminate the impossible, what's left is the solution, no matter how improbable.

I don't think it's possible that the piston that caused those marks lived to tell about it. As a result, I don't think we're looking at that piston.

Therefore...

Let me tell you a little story:

Years ago, a buddy of mine bought a raggedy old 500 Triumph twin for something like $150-$200 and was all excited to get it running. So he brought it to me; but try as I might, it COULD NOT get it to give me a decent, balanced idle.

We did a "dry" compression test, one cylinder was within spec, one was considerably higher. Dry.

Plus the thing was peeing oil everywhere from the pushrod tube seals, so we popped the head off to have a look-see (and replace the pushrod tube seals.)

The sight that greeted us was a real surprise. The bike had one standard, flat, stock Triumph 500 piston, and one highly domed fly-cut racing piston (the higher compression side.)

We replaced the push rod tube seals, and buttoned it back up. I got it running as best as possible; and he rode it for a couple months and sold it.

So yes, people WILL go through the trouble to replace just ONE piston in a motorcycle engine.

 

How about this???

The One-Hole went Lean and ruined the Original Piston.
Somebody took the trouble to put-in the wrong Piston.
The searing is from the over-heat.
The "Stutter" marks are from Blow-by.

It's amazing that the Motor didn't "Throw a Rod"

I'm just guessing.
But there signals in a lot of the pix that make me think the Bike was run with a condition that allowed a lot of unburnt gasses to cause enough Carbon build-up that you'll be spending time getting rid of that accumulation, too.

 

at this point, go ahead and remove piston as well for examination?

 

Yes, it would be the next step anyway. I'll have some observations and a few more questions for you this evening.

Just the "ugly" one; the others should be fine, so no sense having to buy 8 new circlips instead of 2.

 

Hang in there kid, these guys take a while but you can't beat the free, CORRECT education!! Next bike you have, you will fear no project!!

I'd give my left n** to have an hour with that engine! Not really, but you get the idea...I'm the curious type and the suspense is killing me!! <LOL>

I almost would have bet money that there waqs a. a cracked piston b. a cracked or upsidedown ring.

Hmmmmm

jeff

 

haha ya I really do appreciate all the advice from everyone. this website is the best knowledge available for anyone with an XJ series bike.

update: mom has me busy working today around the house so I'll get to the engine tomorrow or late tonight. we just got 5~6" of snow so its not like I'm gonna be wanting to ride this wknd anyhow lol. once i return to school start of next week I won't be able to wrench on the bike as much obviously... :cry:

 

You and me both, brother, you and me both; and on both points.

The piston is being pulled for closer examination; the fact that the smallest feeler in the set wouldn't fit in the land next to the 2nd ring has me highly suspicious of its condition.

Maybe it's not cracked; maybe it's distorted or "smooshed" from overheating.

The pistons in these bikes EASILY melt if overheated; you can quickly "hole" a piston running overly lean, so I'm suspicious of that piston at this point.

 

was doing a little search on ebay and came across these piston rings. I understand they are 1st oversize rings but anyone know why there are extra rings? i only need 12 in total (top compression, 2nd wiper, and oil rings)