Compression test question

I have a question about doing a compression test on a yics motor. Now I'm sure no one does this but the thought came to mind the other day. Would it be necessary to blank out the yics passage to get a more accurate compression reading by further isolating each cylinder? Or is the passage small enough for it not to matter? Thoughts? Overkill perhaps? It's on a 82 xj650

 

Interesting thought, YICS open or blocked won't increase CFM of air being drown in by the piston. I believe this passage is before (upstream) of intake valve.

 

Compression should be measured under conditions that replicate a normally running engine. The specs assume that the engine is warm, and the throttle plates are open. If you block the YICS system you aren't simulating a normal operating condition.

 

Gotcha , thanks for replying guys. I just checked my valve clearances. Waiting for my shim removal tool to come in the mail today so I can get shim sizes. Anything else I should check while it's open?

 

Shim removal tool:

 

I've seen this method on here and as I've seen ppl have there mixed reviews on the subject of sticking things in-between the valves for risk of either breaking off peices of carbon deposits around the valve seat and or breaking off peices of wire/ zip-tie whatever you use. I see you are confident with this method though and have been around for quite some time.

 

I have the tool, I tried zip ties, the wire is the way to go no doubt about it.
reworking the wire is easy but the tool needs to be modified to work grinding down the sides. I use the 2 I have as paper weights

 

I tried the tool. modified the tool, still wouldn't work in some positions on the head. I went with zip tie and never looked back. If a bit broke off, it would melt and be expelled easily enough. Copper wire sounds good as well.

 

Well then, looks like I'll have myself a brand new paperweight waiting for me when I get home today. And as far as compression goes I did things out of order a bit. I did a comp test before checking my clearances. Results ranged from 119 being the lowest and 130 being the highest and the other 2 were just above 120. Low readings for a 650 correct? With what readings I got for my clearances does this seem about right or should I squirt some oil in there and see if rings may be stuck. Carbs have been thoroughly cleaned but did not break rack. I was sure to clear blockage in the starter jets in side the well in the bowls. But still have a bit of a hard time starting cold. And doesn't idle for shite. It's been real temperamental.

 

I'm hoping I'll find out more once I get those out of spec valves back to where they need to be and go from there I suppose.

 

Well Bacon (your name is BACON!!!!!!!) you obviously have been lurking and reading so good for you AND welcome aboard.

I have the tool, never modified it and use it. There are times when I have to reposition it as it doesn't quite find the lip of the bucket if you aren't lined up perfectly. Not a big deal for me, I sit on a chair next to the bike, not in a hurry and take the extra time.

P.S. less of an opportunity to cross thread the spark plug hole.

 

I talk to mine nice so they won't get cross.

 

I like to whisper sweet nothings to my carbs in hopes that it will cooperate with me

 

I had issues with the tool on my 550 engine. I suspect larger engines use a different casting (but don't quote me on that). What got me was one of the bosses for a bolt.. don't recall which one. I just couldn't get the tool to line up properly for those close to that boss.

 

I have only used a wire. Never had any issues. I have had a shim crack in half when I removed it, but no problems with valves, clearances, or compression weirdness resulting from the wire. My only compression weirdness came from a bad torque wrench.

 

I'm gonna give the tool a shot when I get home, see how much of a fuss it gives me. Seems like I might have bought myself a bunch of useless tools as I had bought the yics blanking tool as well.(I'm a big fan of having the right tool for the job). The bike has 15k on it currently

 

it is always a good base line if you do it before shims you get the pleasure of seeing it improve.
if you want to treat stuck rings use atf and acetone mix 2to 1 ratio it will ffree them you may have to treat and retreat to get results..
just putting oil in is to see if the rings are why you have low compression in the second test

from info overload
h) If the readings are below spec, then shoot about a teaspoon amount of motor oil into each cylinder, crank the engine over a few revolutions with the starter (to spread the oil around), and then re-test each cylinder using the above procedure.

i) compare the two results and analyze.

XJ650 and XJ750 air-cooled engines:
Minimum: 128 psi
Standard: 156 psi
Maximum: 171 psi
Max. variance between lowest and highest: 14 psi

info over load also explains how to interpret your test results

The Information Overload Hour

 

could you tell us comp for cylinder 1 2 3 4 to compare it to your valve clearances

I would suspect cylinder 2 as the worst based on your clearances

 

Hmm well this kind of worries me a bit as 2 of the cylinders were within spec. And we're not anywhere near the standard and about 5 psi shy of the minimum.

 

What were the numbers? You try the weak cylinders with oil as well? Engine warm?

 

Cyl 1. 121
Cyl 2. 119
Cyl 3. 130
Cyl 4. 124
I'm going to check again once valves have been adjusted. Hopefully an atf+acetone mix will help

 

Battery fully charged? Butterflies wide open?

 

air box open filter removed

comp valves Intake spec .11-.15 Exhaust spec .16-.20 comp spec min128 standard 156 max 171 spread 14 psi

Cyl 1. 121 I .10 E.18
Cyl 2. 119 I.10 E.13
Cyl 3. 130 I.13 E.18
Cyl 4. 124 I.13 E.18

not all testers are accurate , and you are with in the 14 psi spread I do expect to see improvment with shim change

 

Fully charged battery, airbox filter NOT removed, I will be sure to do that as well. Now I thought we wanted the tests to be as close to normal running conditions when doing this or is that for something else?

 

I go by the info overload method of testing. as long as you test the same way every time its all good.
air filters can be dirty and restrict flow of air if you want to test with filter in it should be new.

 

Alrighty then, I will add new air filter to list of things to replace. I just blew it out with some compressed air.

 

Will 10g be ok or is that too thick?

 

A small flat screwdriver makes a good shim removal tool. Never had any luck with a round piece of wire. A thin pair of needle nose pliers or tweezers to pick the shim out. Wire could be used to hold the valve, I use a plastic wire tie for that.
Wire or wire ties to hold valves open can dislodge carbon and give false readings when rechecking clearances.

 

Ok so shim is kinda stuck in the bucket..

 

10 g will work.

 

He was refrencing the bucket holding tool.

 

There is a notch in the bucket so you can use the screwdriver to lift the shim.
I prefer to use a magnet to remove the shim once it is loose from the bucket.

 

Alrighty, I was successful with the proper removal tool only because it helped keep the bucket pinned down while I used a small Flathead to pry up to pop it out ... On to the next one!

 

Will it be ok to leave the out of spec shims out while I rotate to the next valve or will this cause damage?

 

You will ruin the buckets, and possibly score the cams if you do that, so DON'T DO THAT.
Every bucket needs to have a shim in place when you rotate the engine.

 

Write down the clearances, write down the size of the shims (put them back like Kmoe said). Then do your figuring and if Lady Luck is on your side you can do the shim dosey doh. . . However you do need at least 1 extra shim to swap things around.

 

Wooo! Looks like I'll be able to do the shim dosey doh and only need to buy 1 shim....Not bad.

 

I picked up some plastic place holder shims from chacal. something to think about when it is time for the next time

 

I snagged a bunch of shims on E-bay for $10 shipped. None of them that I could use to set specs, but all are useful for placeholders, and I can grind one thin enough to use if I ever find a zero-clearance valve.

 

If you're going on a shim purchase spree, it might also be a good time to pick up a few sizes of valves that are close to tight, i.e., An exhaust at 0.16mm or something. They're relatively cheap, minimizes your downtime next time.

 

Maybe, but in-spec is in-spec.

 

Sweet, thanks for all the advice good sirs. I'm going to call the bike shop down the street from me. They should have shims there.