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gs850 gt top end rebuild

  • Thread starter Thread starter mottacycle
  • Start date Start date
M

mottacycle

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Hey guy need some knowledge I got the head off and another one getting cleaned up and valves cut and seat lapped. Also getting the valve lash adjusted. Gave him the cam so he could do so. Is their anything I'm forgetting?? as I'm doin the top end should I replace the rings while I have it off, cylinders look good no scratches. If I should replace the rings how should I go about doin that hone with bottle brush and replace them?? Anything else I am forgetting I'm ordering head gaskets and valve seals. Thanks for the input I'll post some pics when I get off work
 
How was the compression? The oil usage? How many and what type of miles on it? Did you own the bike since new or is it an unknown? Are you trying to go low budget or going all out on it?

If you don't replace the base gasket it is likely to leak anyway after pulling the head, especially if the cylinder isn't still stuck to the cases. For that you need to pull the cylinders. If you want new rings that is the time.

Rings can last well over 100,000 miles, or they can be destroyed in a heartbeat, it's up to the rider. There are specs in the manual to determine if the rings are still within limits. A lot of people just put new rings in any time they have the head off. Some never do unless they are wasted. Up to you.

Bottle brush hone is fine as long as there isn't a lot of wear in the cylinder.
 
Most foolproof thing to do is install new rings. Use a 240 grit bottlebrush flexhone and have at it. It's critical to use good quality gaskets, and OEM is the most reliable gaskets available. There are some okay quality aftermarket gaskets but it's a crap shoot. What ever you do don't purchase any green Athena gaskets. Those things are pure evil.
 
Has 26000+ miles on it not original owner compression was low across all cylinders bout 35psi +- Oil usage was good. mile usages unknown. Cylinder walls looked good. Ill try and get some pics here tommorrow. Base gasket will be replaced as with top cam cover gasket and the rectangle gasket around the cam chain opening. Any who I figure the low compression could have been a number of things, rings valves, base gasket. Etc so I started with valves and rebuilding head from 80 gs 850. And new gaskets and valve stem seals. But my concern I guess is if it is the rings then I should have started bottom to top.
 
More often than not poor compression is traced to idiots that don't adjust the valves. Compression goes down as the clearance goes away and the valves hang open and eventually burn. Adjusting the valves often restore compression, because GS engines are tough, but not always. Storage reduces compression too. You should never perform a compression test on a cold engine that hasn't been run lately. The rings tend to stick in the lands after prolonged storage and typically some good hard miles (Italian tune up) increases compression noticeably.
 
alright then that makes me feel lots better bout the route i have gone. i wanted a solid top end, and then work from there. one major question about the buckets though.. they are not adjustable.... as my machine shop guru has said so this is why the valve lash must be correct. within .001-.003 in my book as i remember. to my understanding though u can use shims on the bucket to correct if needed after 100 miles or so?
 
Your "machine shop guru" is sorta on the right track. Yes, the clearance has to be correct, and the clearances are TIGHT. When you do your measurements, be SURE to keep track of your units. The clearance limits specified are 0.03-0.08mm, which is close to 0.001-0.003". Notice that there is a "3" in both measurements, but one is minimum, the other is maximum and there are a different number of zeroes between the decimal and the three.

For a little bit of help keeping your clearances straight and figuring out what shims you need, look up member "Steve", look in his signature. He has a spreadsheet that really helps with this. Also, make sure you use the correct method to measure clearances. The Haynes and Clymer manuals are not real clear on this, the Factory manual outlines it well.

.
 
What about new valve guides as well? Is this also something to be replaced due to age?
 
alke46 said:
What about new valve guides as well? Is this also something to be replaced due to age?
Click to expand...

Measure using the wobble test as detailed in the manual. Only thing, the manual allowance is way too loose in my opinion.
 
They valve guides rarely wear out, especially with such low miles. All of the forces on the valves act straight up and down, the 8 valve engines are very easy on valve guides no matter how hard the engines are abused.

Check them and you will know, but I haven't had to replace any yet.
 
thanks datsa! for the tips. i have a service manual for the bike just didnt have it in front of me when my brain rattled off that spec lol!! but now u got me confused... spec sheet says Valve Clearance or tappet (when cold)IN. 0.03- EX.0.08 then below(.001-.003) i mean tight is right but which is it?
 
.03-.08 mm.

Tight is not right, loose is. The valves tighten with mileage.
 
Guess somewhere in between also I will go with factory gaskets but the vit seals it's a 81 gs850gt
 
No, do it right. Quit thinking in inches, it's millimeters. Use the Suzuki manual, the others are wrong. Use the right method, use the right tools, it's easy. Burnt valves suck.
 
UUUuuuhuhuhuhuhuhuhhhhhhhhhhhhhhhhhh. That Lurch noise. Again.
 
Last edited:
mottacycle said:
... spec sheet says Valve Clearance or tappet (when cold)IN. 0.03- EX.0.08 then below(.001-.003) i mean tight is right but which is it?
Click to expand...

The 0.03-0.08 spec is in milimeters, the 0.001-0.003 spec is in inches.

Both are correct, but the mm spec is MORE correct, as the inch spec is an approximation.

When you are deciding which shim to use, go with the looser side of the spec, if possible. Unfortunately, one shim size will change by the entire range, so if you are at 0.035mm, for example, going just one shim size thinner will take that to 0.085mm, which is technically out of the range. The good news is that you can safely go to 0.10mm (approx. 0.004") with no problems. In fact, the bike will run just a bit better with looser valve clearances, and it will be longer before the valves get tight enough to need another adjustment, but you still need to check them according to schedule.

If this bike is 'new' to you and you know nothing of its history, plan on checking clearances again soon, likely within 1000 miles or so, just to make sure they are still good. After that you can go to the recommended 3-4000 mile intervals.
 
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