GS850 Head Gasket and Piston Ring Replacement

[Guest]

Hi Guys,

Just wanted to firstly say thanks for all your posts - this forum has been a blessing and a charm to read over the last year - Really helped me out! Anyway I've struggled to find some advice on piston rings, apologies if this is on another thread...

STORY:
Bought an '82 GS850 just over a year ago, have been doing bits and bobs to it at home but sadly I live in the city of London and you can't swing a wrench here without hitting a cat! So... I've relocated my humble workshop down to my old dears in Andover, nursed the bike down (she was blowing lots of smoke and could barely make it past 70mph without really struggling ) and am doing a top end rebuild - All gaskets and probably piston rings...

I've come to this conclusion because the bike's got a pretty bad oil leak from just in front of cylinder 1 (head gasket?), it blows quite a lot of smoke apparently (I don't have wing mirrors so I can't really see...), I did a compression test and every cylinder apart from 3 was at 75psi, cylinder 3 was at 100psi and I also lost a lot of oil on the journey down...

So my question is do I just need to get the same sized piston rings as in the manual or do I go for oversized taking into account the wear of a 35 year old bike? And does anyone know any good places to get these rings in the UK?

Many thanks,

Fred

[Nessism]

First thing is to measure the pistons and cylinder to find out how much wear there is and compare the specs to the factory Suzuki manual for your bike (manual download available on Basscliff's website). If the bores and pistons are stock and still in good shape then you can install new stock rings and give the cylinder a good bottle brush hone job. Oversize rings are for use on oversize pistons, and to install such parts your cylinders need to be bored and honed oversize.

[fastbysuzuki]

Hi if you need standard rings suzuki will charge around £54 per piston here in the uk, they are cheaper in the USA great if you have a relative there that can send to you labelled as a gift to escape the dreaded duty.
There is a firm here in uk that has had a batch of standard rings made up for the 850 they have them on eBay Here
i have used a set and have had no problems they also have the gugeon pin/piston circlips cheaper than Oem.
If you remove the pistons Do not attemp to use the old circlips.
The general feeling on here is to use genuine suzuki head and base gaskets and orings make sure you are sat down when you phone for a price on the head gasket

[free_derick]

Amazing thanks for replying - better hunt down a bore gauge this weekend then!

Thanks for the advice on the piston rings - I guess I'll get a closer look this weekend at how many ring (hopefully not all!) need replacing. I bought an Athena gasket kit, they had mixed reviews online but thought i'd try first before forking out for oem... gobsmacked at the prices!

If anyone happens to live in the Andover UK area and is around this weekend with a bore gauge, I will repay the favour of a lend with beer and/or cake!

[2BRacing]

While you have the head off, you should also measure the clearance between the valve stems and valve guides. The guides will have to be replaced if the clearance is out of spec, and also definitely replace the valve guide seals. Cleaning up the valves and valve seats by means of lapping should also be done to ensure a good leakproof seal.

[bwringer]

How many miles are on the bike?

It would be very odd if a GS850 actually managed to wear out its bores in less than 150,000 - 200,000 miles or so.

[free_derick]

Thanks 2BRacing - will have a look at the valves. I'm pretty green in the way of machining terms so by when you say clean by means of lapping, are you saying (in layman's terms) clean the valves and seats with a some abrasive and polish up?

It's got around 85,000 miles on the clock so hopefully won't have worn down much or at all.

[fastbysuzuki]

Thanks 2BRacing - will have a look at the valves. I'm pretty green in the way of machining terms so by when you say clean by means of lapping, are you saying (in layman's terms) clean the valves and seats with a some abrasive and polish up?

It's got around 85,000 miles on the clock so hopefully won't have worn down much or at all.

You will find a tutorial Here personaly I would not use a drill or whatever to spin the valve, use a stick with a rubber sucker like the one Here and grinding paste Here
Make absolutely sure you have washed off any remaining grinding paste when finished.
when all the valves have been refitted pour some petrol down each one from the cam housing side and check there is nothing seeping past the valves.

[2BRacing]

^ Yes. And another Yes to use the stick and sucker instead of a drill - the valve face and valve seat will quickly "lap in" just using the stick. You are done when both the valve face and the valve seat have a grey-coloured sealing surface of even width all around.

Push the rubber sucker onto the valve head, and hold the stick between the palms of your hands. Roll the stick back and forth between your palms, as if you are trying to start a fire without a modern lighter.

[hannibal]

Found this vid on lapping valves: https://m.youtube.com/watch?v=7GEmuQa3dPY

[free_derick]

Hi Guys,

Thanks for all your help - made some progress on the weekend but had to wait around for a friend's Valve Spring Compressor so didn't get as far as I wanted on the valves - made use of the time polishing up the pipes though... very satisfying!

I took the cylinder head off expecting to see either broken piston rings, scored cylinders or a broken head gasket... I don't really know what I'm looking for but to me they all looked fine None of the rings were cracked or broke, the cylinder looked pretty good although I know this can be minute and best to measure! And the gaskets were not broken... so where is all this oil coming from and getting into my combustion chambers?

The combustion chamber and cylinders were covered in carbon as you can see from the photos, especially the exhaust valves... my theory is that my valves are leaking and don't have a good seal which is giving me the low compression and the oil leak - does anyone know if I'm poking in the right direction?

Cheers

IMG_6548.jpg

[free_derick]

[Nessism]

The valve face photo indicates that valve was hanging open and not fully closing. A classic case of someone neglecting valve clearance adjustment. Hopefully all the valves don't look like that. At minimum you should decarbon the entire head and test lap the valves into the seats to see how much damage there is. Personally, I'd get the valves faced before attempting the lapping.

[free_derick]

Hello,

Finally managed to put the head back on this weekend and the bike back together. Tried to start her up but was getting nothing... probably should have checked this first before I put her all back together but it turns out I am getting zero compression from all cylinders - I'm assuming this means that I've buggered up the valve timings?

When I was putting the cam chain back on it said in the manual that the exhaust cam arrow has to point forward and ever so slightly down, however when I got the pistons to TDC it never was completely in alignment. Either the exhaust cam arrow was pointing too far down or up when I had it at TDC... I took a 50/50 decision and went for the arrow pointing further down... My plan is to take the cam cover off and try it the other way round, if anyone has any other sound advice or has been in this situation would greatly appreciate some sound advice! Haha - hoping to get her on the road soon as am missing some b-e-a-utiful bike weather!

Cheers,

Fred

[JTGS850GL]

I sure hope that you didn't bend any valves. If so, you'd be pulling the head off again.