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Did compression test, here are results. Please help diagnose!

  • Thread starter Thread starter defwack
  • Start date Start date
D

defwack

Guest
I just did a compression test on my 1980 GS850G, and here are the results before and after adding a tsp of oil to the cylinder;

Cylinder 1 (leftmost):
110 psi / 170 psi (after oil)

Cylinder 2:
65 psi / 110 psi

Cylinder 3:
105 psi / 118 psi

Cylinder 4:
110 psi / 130 psi

From reading around here, I am guessing this means my rings are bad? Is this an accurate assumption? How much would this sort of thing cost to get fixed, and is it something I can do myself or would I have to take it in somewhere?

Thanks!
 
A few things about the compression test. Usually done with the bike warmed up and the throttle must be wide open. Helps to have the valves adjusted correctly too.

The important thing is for your cylinders to all be within the same range. 100 psi is about minimum. Assuming that you did the test right, yours are at the low end and #2 is way to low.

Usually if you do the rings, you might as well do the whole top end (valves too). Much of it you can do yourself, but any machine work you'll have to take elsewhere.

Having said that, how many miles are on your bike? How's it run?
 
I did the test with the bike warmed up and the throttle open, and followed the directions that came with the test-kit as best I could. I'm fairly certain I did the test correctly, so I'm going to assume the numbers are accurate.

The bike is pretty high up on the mileage scale... clocking in at about 80,000. The bike does run alright for the most part. It starts on the first try with a little choke, but does have some idle problems. I know there's a small problem with the throttle cable, so I'm going to replace that soon. There's also an air leak in the H-shaped exhaust connector under the bike, so I'm going to fix that too.

My only real concern is the compression, since I don't have a lot of money to get things professionally fixed, and I live in an apartment so it's hard to do any work on my own that'd take more than one day.
 
Sounds like you're sort of at a dead end unless you can get a place to work...doubt you can do a top end job out in the parking lot. :)

This is just a shot in the dark.......but you might get lucky. Some guys swear by stuff you can get at Wall-Mart called Marvels Mystery Oil. Throw a teaspoon or two of that stuff in cylinder #2, crank it over a few times and wait for a day or two.

You might have a stuck ring in #2 that is causing your low compression. If that was the case and you freed it, you might get all your cylinders up around 110 and be home free. On a bike with 80,000 miles I'd take that in a minute and enjoy the ride.
 
Have you verified valve clearances?
If the valves for #2 have too little clearance, that could be your problem right there.
My bike's compression was much better and ran so much better after adjusting the valve clearances. It makes a world of a difference.
 
How would I go about adjusting the valve clearances, or even checking them in the first place?

Also, doesn't the "teaspoon of oil" test pretty much confirm it's the rings?

I will try to find some of that oil stuff at Walmart, and cross my fingers. I would much prefer a little goo to engine work!
 
Suzuki 850G manaul says standard compression is 128 to 171 and list the service limit ("overhaul required") at 100psi or a difference between cyclinders of 28psi.

Yes, the compression did improve with adding the oil, so, yes, that does indicate that the cyclinder/rings are not sealing well. But even with the oil the compression readings are not all what it should be. So must be more problems than the cyclinder/rings. Checking the valve clearance (and reshimming as needed) could help the oiled compression readings, but you will still have the cyclinder/ring problem.

Somebody beside me will need to answer about how bad are reading like that as far as how it effects prefromance. The manaul talks about "service limit", but I dont know if that means it will not run, or if just not run well, or what.
 
defwack said:
How would I go about adjusting the valve clearances, or even checking them in the first place?

Also, doesn't the "teaspoon of oil" test pretty much confirm it's the rings?

I will try to find some of that oil stuff at Walmart, and cross my fingers. I would much prefer a little goo to engine work!
Click to expand...

Valve adjustment is basic maintenance and they need to be right or you'll do damage to your engine...in other words, it ain't optional even if you don't have compression problems.

You need to get a manual for your bike, Haynes or Cylmer. You'll also need a valve adjustment tool made specifially for that purpose on your bike. I got mine at JC Whitney for about $30.00 but there are other places that sell them as well, maybe cheaper. You'll also need a set of feeler guages that go down to at least .04mm. These are very thin, and a bit of a specialty item but I found a set at NAPA. You'll also need a ratchet with the correct socket to manually turn the crank on your engine.

Essentially, you pull your valve cover (which may involve replacing the valve cover gasket) measure the gap between the cam lobe and the valve shim when the valve is closed and the cam is in the correct position, which happens by you turning the crank counter clockwise. If the gap is too wide, or too narrow, the valve adjustment tool will compress your valve so that you can remove the valve shim and replace it with the right one that will give you a gap within the proper range (.03-.08mm, I believe). You can get valve shims at your dealer or cheaper on-line.

Manuals are about $20.00, tool $30.00, feeler guages $10.00. gasket might be around $15.00 on-line, valve shims around $5.00 a piece give or take.

Lots of people here will help you do it, its something you really need to learn how to do if you're going to have that bike. :)
 
defwack said:
The bike is pretty high up on the mileage scale... clocking in at about 80,000.

My only real concern is the compression, since I don't have a lot of money to get things professionally fixed, and I live in an apartment so it's hard to do any work on my own that'd take more than one day.
Click to expand...


Simply sounds like to me you have a worn out engine. The fact that engine went 80K is MORE than can be expected of any motorcycle engine. A tell tale sign of worn rings is when the compression come way up after adding oil. A lot depends on the gage you are using also. You guage might read different than mine. My GS1100 reads about 150 psi, but more importantly 150 psi on ALL 4 cylinders.
 
Heck, when I was in the dorm at Luke AFB I rebuilt my 302 in my room. The only hitch was trying to go down the 2nd floor stairs with it. You should of seen my 1st Sgt when he moved the bean bag that was hiding it and said what the hell is this. I told him OJT.

If you got the room and clean the parts do it in your room. Just put a blanket over it and if anybody ask's tell them it's a couch.
 
Carlos, You may want to post in a separate thread... hijacking the other fella's thread doesn't make answering easy... Thanks


defwak - First thing is that you had best quit making assumptions. If your bike has 80K miles, pull off the cylinder and measure the cylinder bore and piston diameter and see if piston to bore clearance is within spec. If the cylinder bores are too big and the pistons too small, new rings will only be a waste of money. If the clearances are out of spec, you have a couple options at this point...

a. bore cylinder and install new pistons/rings: You will have about $600 in the pistons and boring PLUS gaskets and other costs associated with work that should also be done
b. buy new cylinder w/matching pistons from a lower mileage bike - measure clearances and if they are OK, hone/re-ring. You will have about $100 in a used block/pistons and another $100 in new rings and cylinder hone plus a gasket set and have to fork out for other stuff...

If the clearances are OK, you can obviously use new pistons but you can also get away with rings and honing.

The secret here is measuring THEN making a decision on where to spend money. A used block and matching pistons from a low mileage bike will work as well as new, oversized pistons for the most part.

You will want to split your cases and put in a new cam chain and other cam chain related bits... this is REAL GOOD MONEY SPENT!

I would also pull the cylinder head apart and measure valve stem length. This is a great way to determine how much life is left in a cylinder head. If the stem length exceeds spec, you will need new valve seats and it is probably also time for new valve guides. If they are within spec, clean them with a wire brush wheel and lap the valves/seats and install new valve stem oil seals. You will need a valve spring compressor tool with the proper adapter. It takes about 3 hours to completely clean up, lap and install seals on a head that is within spec.

I would definitely buy a manual. An experienced hand can rebuild the ENTIRE engine including cam chain (case splitting) in about 2-3 days. The big bulk of the time is actually cleaning gasket mating surfaces and chasing out case bolt threads (I do this on every rebuild) with a tap.
 
Sorry

Sorry

Heyyyyyyyyy defwack I am sorry I did not mean to step on you. I will re-post thank you
 
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