Still no compression

[facepants]

Left cylinder wasn't firing, found out that it had very low compression and was burning oil.  Took it to a shop and had a leakdown test done.  The mechanic told me that it was either bad rings or the cylinders/pistons were out of spec, and that it couldn't be the valves because they were sealing properly (which he supposedly deduced through the leak down test). 

I tore everything down, had the cylinders deglazed and measured, also cleaned and measured the pistons, both were within spec.  When I went to pick them up, the same mechanic told me that I should put new rings in, but he's never heard of bad rings causing low compression and oil burning via blow-by, so if new rings don't work, it's the valves, which is exactly the opposite of what he told me the first time.  I said "didn't the leak down test tell you that it was pistons/cylinders/rings" and he said "it doesn't tell me where it is, it only tells me where it isn't".  Then I said "didn't you say it wasnt the valves?"

Crickets.

When I got home I checked out the valves following advice given by scratch, flip the head over and fill the combustion chambers with kerosene.  No leak.

I just finished putting everything back together, new rings, clean pistons, honed cylinders, clean valves, new gaskets... the works.  Tested compression... it's even worse than before.

It used to be 30 on the left and 100 on the right.  Now its 0 on the left and 90 on the right.  I put a teaspoon of oil into each cylinder and re tested compression (something i found on the board to test if its the rings).  No change.

Any ideas?  Could it actually be the valves somehow?  I don't see what else it could be....

[coll0412]

Yeah you should have just had the valves done while you had it apart

Did you also do the test with the throttle wide open...just checking

You replaced the rings on both pistons right?

[facepants]

Replaced rings on both pistons

The throttle cable is actually detached, as are the carbs, airbox and exhaust.

Would open throttle make a difference?

[facepants]

I guess the throttle wouldn't really make a difference since its attached to the carbs   

[anthonyd5189]

Im not exactly sure how the GS engine is layed out, so Ill just say what to do in a car with the same thing.

1) leak test, if its not leaking then the problem with compression could be valve timing possibly, a valve open while on the power stroke?
2) if it is leaking, make sure valves are closed during the test, if your using compressed air, the air can actully move the piston just enough to open a valve.  If they are shut, could be the rings or gasket(if there is one).

The only way an open throttle and exhaust would matter is if the intake or exhaust valve are open during the test, if they are closed then no need to worry.  If your doing the test and it leaks, take a listen at the exhaust pipe or the throttle body to see if you can hear air coming out.  If you do then you know which valve is leaking.

Thats as much as I can come up with

Edit:  Just saw another thing in your post.

When I went to pick them up, the same mechanic told me that I should put new rings in, but he's never heard of bad rings causing low compression and oil burning via blow-by, so if new rings don't work, it's the valves

Burning oil and low compression together would point to bad rings.  If the rings are not sealing, theres your reason for low compression.  Again if the rings are not sealing, a more than normal amount of oil will be getting up into the cylinder causing your exess oil burning.

I hope that this all helps, if I'm way off I'm sorry, haha.  But given your problem and what you have said it has to be the rings or valves.

[Lukewarm Wilson]

think did i fit the rings properly with the gaps oppisite each other and right way up, or sticky valve thats just my thoughts

[facepants]

Yeah, put in the rings correctly according to the haynes manual, so I'm pretty sure it isn't the rings this time.

How would it be the valves if they are sealing (no leaks with the kerosene test)?

I've had this thing since October and only rode it 3 times.  I'm thinking about running it over with my car.

[Jughead]

Hmmm Sounds like your head is warped.That Cylinder Gasket is just a Thin Sheet of Steel.Actually it really didn't seem like it would even Compress Enough to seal if the head was Warped the Least bit when I tore my Motor down.Why they Didn't use Copper,Aluminum,Asbestos Etc. I don't know. Did you use a Sealer to Seal it to the Head or Cylinder?If you tear it back Apart Lay it on a Flat piece of Glass and Check for Warpage with some Feeler Guages.If it's Warped you can Probably Lap it back flat in no time with some wet and dry paper or Valve lapping Compound.Chances are that if it is Leaking it will be leaking thru to the Center where the Timing Chain Rides.It will probably be hard to measure there soPut a very thin Film of Oil on the Gasket Surface and lay the Glass on the Head and look to see if there are Any Places where the Oil isn't showing on the Glass.
You could Also drop a few Drops of 2 Stroke oil in the Cylinders to Wet the Rings and Bore to see if your Compression Comes up Some.If it does it's your Rings.

You know I think I may have some GS450 Head Gaskets that may just work in place of the Steel Gaskets with a Little bit of Modification.They are Sandwiched Aluminum with a Fiber/Rubber Surface and are much Thicker and a little more Expensive.

[facepants]

Hmmm Sounds like your head is warped.

Good tip, I thought about that flimsy gasket briefly when I bought it, but it hasn't crossed my mind since.

I didn't use a sealant, just the gasket.  Would smearing a good layer of high temp sealant on both sides of the gasket suffice? 

I'm not sure I'd be able to find a piece of glass or flat enough surface to see exactly where it is warped and sand it down until it isn't.

Already did the oil in the cylinders trick with no change so it's definitely not the rings.

[Jughead]

I updated my Last Post.Should have Post in a Seperate Post.I would say if it is Warped and you did use a Sealer it would Hold but for How Long. Usually if it's warped that bad it will keep getting worse until it's Lapped/Milled Flat Again.It may Hold forever or Blow back out at the Worst Possible time.
IF I have a GS450 Head Gasket that would Probably Fill in Enough Space to seal it.The GS gasket is Much Thicker and Will Compess when the Steel one won't.IF I have one I can Compare it to the Old Steel Gasket from my Bike to see if it could be Modified to work. Since it is Thicker you will have Slightly lower Compression though.

[facepants]

IF I have one I can Compare it to the Old Steel Gasket from my Bike to see if it could be Modified to work.

That'd be great if you could let me know.

[Jughead]

Will Do. Seems Like I got one in The other day.

[facepants]

It appears to be warped.  I borrowed a glass table from a friend and tried the oil thing, but couldn't get a clear result.  Then I tried feeler gauges.

On the left side (the side with the problem) I could go around with an 0.10mm blade, but it was a tight fit.  With an 0.09mm blade it slides in like butter.

Around the right side, the largest I could get in there was an 0.06mm blade.

Is a 0.03mm-0.04mm difference a significant amount of warpage?

[Jughead]

According to my Clymer Manual .10mm is the Service Limit on Warpage.

I just went thru my Big Box of Gaskets to start listing some on Ebay.I do have a GS450 Head and Base gasket.I'll try to get up to the Shop in a Little While and see what I can come up with if I can Stand it outside.

[The Buddha]

It will leak oil from the head with that big a warp. But hey you can deck it Its not a loss ... Ok much of a loss ...
Cool.
Srinath.

[facepants]

Is it possible that the top of the cylinder block that meets with the head could also be warped?

What's a fair price to have the head decked?

[Jace009gs]

to get the head milled it'll probaly run you about $85-$125.  BEFORE YOU GET IT MILLED know EXACTLY how much CLEARANCE there is between the valves and the pistons...or you'll be hearing more than a crink-de-crink.......With it being .09 on one side and .06 on the other it sounds like the bolts arn't even/ or the head surface is warped. For them to mill it out I WOULD GO THE EXTRA STEP and get them to mill out the valve seats and put in new valves. Their cheap insurance and the valves have to be removed before anyone will machine it.....

Other things that involve compression other than rings:

1. Valve job- to close the clearance the valve may not shut all the way, and/or the valve seat is worn/warped too remember to check at TDC......Measure the valves and get back to us...I be 99% the valves are wacked out of spec....
2. dirt on the cyl. head gasket upon instilation- you did scrape the old gaskey right? and light sanding of the surface?
3. BAD INSTILATION OF THE HEAD meaning
     don't re-use the head bolts- they stretch after use, always use new hardware
     USE an air gun to blow out oil out of the threads -can get bad tourque reading with oil down the threads
     USE A calibrated tourque wrench when tightning
     USE the x-pattern when tightning as stated in the manual

ABSOLUTLY DO NO APPLY HIGH TEMP GASKET SEALER to the head gasket. The head is under high pressure that high temp gasket stuff will just blow out on the first stroke and you'll probably clog up one of the oil lines resulting in a seized bearing......BAD MO-GO....you'll be back to a nice paper weight


Sorry just read about the Kerosean test.....so your valve seats are probably good...but still to machine the head you have to take the vavles out...so measure them and see if their in tollerances...

One other thing I don't know if you honed the cylinders or not but you maybe have an egg shaped cylinder......these won't seal;) please tell me the rings you installed were one up on the bore....Small rings in a big bore don't seal either

Completly irrelevent but you said you put new rings in....Did you replace the crank bearings too...IF not I would pull the motor back apart and put new ones in too.....AKA-your doing a basic motor rebuild from top-bottom.

[facepants]

Thanks...

Sounds like it'd be expensive for the whole job, valves and milling.

1. I checked valve clearance before and after taking it apart and it's good.
2. bought all new gaskets.  cleaned the surfaces of the cylinder and head with solvent.  spotless.
3. all new hardware, cleaned threads with solvent, used a torque wrench, followed manual to a T

The bore is factory as are the pistons and rings. 
Cylinders and pistons were measured at a shop and are still within spec.  Cylinders were not egg shaped.  Were deglazed.
Checked installed ring end gap with feeler gauge and everything was within range so I assume those are the right size.

I didn't replace the bearings, is that really necessary?

[Jace009gs]

well if you spin at 8k rpm for 15k miles your probably going to wear out soon..

but no seriously, the bearings are like $8 a piece. Just as a reference any time the rings wear out the bearings are worn out too. They wear at about the same rate. However, in your case we are not certain the rings were worn