Low compression question

[Guest]

I recently acquired a 1981 1000G with 54K miles showing. It seemed to run well, but had an exhaust leak. Traced this to a missing bolt at the head. The hole was not only stripped, but a previous repair attempt had broken off a hardened object (possibly an EZ out but more likely a drill bit from the size). The best probable course of action was to pull the motor & then pull the head so it could be repaired.

Today, I was reading the shop manual and decided to make a compression check. I got 89-90 PSI across the board. The manual says the range is 128-184 PSI, and the limit is 100.

The paperwork I got with the bike does not show when the valves were last adjusted.

My first question is if being out of adjustment would result in such a consistent low compression or is this a sure sign of worn rings/cylinders?

My second question is more of a what if. After looking at the parts cost and labor (machine shop) involved for fixing the head, I was leaning towards swapping in an 1100G motor. The low compression is icing on the cake. Figuring the valves are close, it makes more sense to me to find a decent 1100G motor and swap it in vs. overhauling this one.

Any thoughts or advice?

[mlinder]

It depends on the compression tester used. Long and bigger the hose, the less compression will show. The fact that they are all within 1psi of each other could very well mean that everything is fine, and your tester is just designed for bigger engines.

Then again, it could be that every one of your cylinders has evenly gotten tired. You can test this by doing a leakdown test.

[bobthebiker88]

why not do a valve clearance check first?

it IS possible that the motor is just tired and due for a rebuild. it might be this, it might be that. until you pull it and actually look, chances are, you simply wont know. all we can do is speculate on the cause. you could always put a little oil in the bores and see if the compression numbers climb up a bit. if the compression jumps, you've got worn rings, otherwise, valves if no change.

[rustybronco]

I would think riding it for a while, then re-checking the compression readings at a later date would be the wisest course of action at this point. that, combinded with checking the valve clearances NOW! and a little engine top end cleaner added to the fuel tank.

unless you realy want to install that 1100.

[DanTheMan]

IF the valves have been a long time out of adjustment, they could at this point not be closing completely. Or, they could be leaking from having built up carbon on the seats from lack of adjustment. At any rate, pulling the head can be done with the engine in the frame, not necessary to pull the whole engine. Get the broken bolt taken care of at the same time you're getting a valve job done. Unless the engine has been horribly abused, 54k is low mileage for that engine. My 850 just passed 88k, does burn some oil (mainly valve guide seals), but still runs very strong. I really doubt that you have a bad engine at this point. If it's been sitting for a long time the rings may be stuck, you may want to put some kerosene or diesel fuel in the top of the cylinders to dissolve the carbon in the rings and free them up. You may find the compression numbers rising.

[GS1000G Shopper]

Thanks all. If the head can come off w/o pulling the motor, that's a big plus. Looking at the shop manual, it wasn't clear. It showed removing the head after pulling the motor.

I have to call a machine shop today & describe what I have/need and see if they can help me.

Rusty,
The idea of an 1100 in it is a natural thing for me. I have a number of cars with larger motors (specifically Chevy V8s) than they were originally equipped with, so why should the GS be any different? I guess it's in my DNA.

[Big T]

GSS,

Yes, it is natural to go big, but less than 10% isn't that much of a change

As for your compression issue, you did a cold test and didn't tell us whether you held the throttle wide open.

The spec numbers are for a hot test, which will be signifcantly higher

So, squirt some oil in the cylinders and retest - if the numbers go up a lot = bad rings. if not proceed with valve adjustment and retest

Did this bike sit for a long time? It may have stuck rings

[salty_monk]

My skunk got faster over the course of about 2,000 miles whilst the rings seated back in... It sat in dry storage for 25 years though.

[GS1000G Shopper]

Big T,
I followed the shop manual- I did hold the throttle open with all plugs out.

I tried to put a uniform amount of motor oil into each cylinder & retested. Readings went up fairly uniformly, now around 145-150 PSI in each cylinder, then back down to around 90 after a few minutes sitting.

I suspect the bike sat for at least 7-8 months prior to me getting it, and it was kept indoors. I have work orders from December 2009 that indicate a shop worked on it & ran the motor- cam chain tensioner reset ("cam chain was loose, engine much quieter now"), reg/rect replaced, checked charging system 13.8V/+- & new connectors added).

For some background, the main problem with it when Tkent02 looked at it for me was a low battery. When it was delivered to me in addition to the battery, the choke cable was frozen. When I rode it home with my helmet on, I never heard the exhaust leak. After doing a lot of static work to it for the fairing & gauges, I rode it w/o a helmet down my driveway, which is where I heard the exhaust leak and subsequently found the bolt problem.

I've read up on the 1100g into the 1000G swap here. Looks like I'd need the shaft to make it work so I'd be best off to find a wrecked bike with a good motor. I''m not so concerned about the wiring. From what is for sale and has sold in the past, I can get a complete '82 1100GL for $4~500 plus travel/shipping. I really don't want to tear the motor apart, but will keep my options open. I'm not going to rush into anything.

I may end up fixing this one if the parts & outside labor are not too bad. I'm figuring the head can be fixed & a valve job done, but the big if here would be the pistons. I'd have to spec everything out, but if the pistons have to be replaced I'm suspecting this would run into big $.

[DanTheMan]

I'm not going to rush into anything.

I may end up fixing this one if the parts & outside labor are not too bad. I'm figuring the head can be fixed & a valve job done, but the big if here would be the pistons. I'd have to spec everything out, but if the pistons have to be replaced I'm suspecting this would run into big $.

54k miles is low mileage. I doubt pistons would need replacing. Rings, yes, hone the cylinders, yes, new base gasket, head gasket, cam cover gasket, all those things if you're going into it that far. The only reason to replace pistons is if the bores are worn out or the pistons are physically damaged. Shouldn't be that bad. I replaced the head gasket on mine 3 years ago, and never did any of that then. I'm waiting for the 100k mile mark to do mine.

[GS1000G Shopper]

Sounds like great advice. I think Mrs. Shopper will be happier if I fix it vs. buying another bike for parts. Any suggestions on where to buy these specialty parts such as rings?

[DanTheMan]

The gaskets (head gasket/base gasket use OEM Suzuki), check PartShark, Bike Bandit,Z-1 Enterprises, Cycle-Re-Cycle Part II, Partsnmore or your local dealer. Rings should also be available from the same places. Price check them, make sure you're getting the best deal. Don't order rings until the cylinders have been removed though to make sure you get the right ones. If someone put in a Wiseco kit or something like that the rings will be different than OEM.
Check BassCliff's site there is a wealth of info on vendors there as well as on the GSR home page links. Hope this helps you out.

[ddaniels]

Paul,
Did you test the compression with a warm engine? Makes a difference. Also, yes the head will come off without pulling the engine. I've done it twice on the same engine.

[GS1000G Shopper]

See above for updated compression tests. They went way up with oil in the cylinders.

I have crunched the numbers for repair vs. replace (ballpark machine shop numbers), and while I could probably make out OK by buying an 1100 and parting out what I don't use, the upfront costs look to be within $100 of each other. Plus, yet another typical Craigslist seller has failed to reply to my email about his 18K mile 1100G motor (went through this hassle to get the bike from Colorado, the seller didn't think I was a real person) he just listed a couple of days ago. Finally, selling parts is somewhat of a hassle.

I'm looking at:
Head repair (machine shop)
Valve job (machine shop)
Cylinder hone (machine shop)
New rings
New head & base gaskets (plus a gasket set with valve seals etc.)
New old stock oil pump (seems like a good idea since I'm getting into the motor)

Hopefully, this will cover what needs repairing and in a few weeks I can start enjoying the bike. Worst case variable in the equation is if I can't find a machine shop here that can do this, I'll have to ship parts to one that can.

Of course, this is all null & void if someone around here wrecks an 1100 with a freshly rebuilt motor.

[GS1000G Shopper]

Par for the course in a small town, there are no machine shops that do work on "small engines". I do have a welder close by that I think can fix the head. Plan B is now to pull the head, and see if it can be fixed. If so, I'll throw on a new gasket, adjust the valves, and see how it goes. The bike seemed to run well the short distance I rode it- no smoke pouring out or anything, so let's hope for stuck rings that will loosen up as I ride it.