GS650 engine tear down

[spottedtango]

Hi guys just a quick update on my gs650L project

Had the engine out and decided to do a compression test out of curiosity. The previous owner had told me the bike was running I know that’s a complete lie as the intake boots had split. The carbs were coated with copper shit inside with all the jets blocked.

Thought I’d share the results.



Engine in question
https://imgur.com/qakQbqI.jpg


Cylinder 1

https://imgur.com/0mtHa1h.jpg

Cylinder 2

https://imgur.com/KOWZ82k.jpg

Cylinder 3

https://imgur.com/PKsc7xk.jpg Which seems low compared to the other two.


Cylinder 4
........Was 0 psi I didn’t take a pic


I’m going to tear the engine down tomorrow but I have a feeling there’s valve damage involved. I’ll try and post a few pics when I get a chance.

[spottedtango]

Quick update,

Stripped engine down and found on cylinder 3 the inlet valve had got stuck open just very slightly with carbon debris on the valve seat.

The other one on cylinder 4 had some carbon build up round the valve seat but not as much.

https://imgur.com/JphpSxo.jpg


I took the two valves out and gave the valves and valve seats a good clean and then tested them some methylated spirits to check they were sealing.

https://imgur.com/LIY2S90.jpg
https://imgur.com/21KPkNR.jpg





Everything seeems ok now.

Has anyone had this before?

My guess is its related to the fuel mixture with the bike running like shit because of the carbs being so clogged up.

[bladerunner]

if its not been used for a long time then yes it's quite possible that dry faces corrode or seals get sticky or the valve itself can bind on the valve guides. Crap can also enter the top end when spinning the motor over etc. new guide seals and a lap of the valves and recheck the gaps should hi light any issues and fix them. The last gs 650 katana I owned killed 2 sets of top ends due to cam wear and both also fudged 2nd gear due to dog wear. the second engine was one from a breakers that had EXACTLY the same issues and the original motor was in that state when I bought the bike cheap anyhow
____________________
Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

[A100man]

If the valves on #4 are sealing (meths test) Then they must have been staying open slightly during the earlier comp test.. Could have been tight/no clearance or some other sticking issue. Did you check the valve stems for 'straightness'?
____________________
Now: A100, GT250A, XJ598, FZ750

Then: Fizz, RS200, KL250, XJ550, Laverda Alpina, XJ600, FZS600

[spottedtango]

When I took the two valves out to clean them I placed them side by side on the bench and they both look identical. So unless they’ve both bent exactly the same way I think they’re ok.

I didn’t realise these engines had a weak top end/2nd gear problem. I’ll keep that in mind if I decide to keep this bike. Depends how it rides tbh.

I was also doing a bit of reading and seen that leaking stem seals on the intake can do this as the oil seeps down the valve stem on to the valve and then due to heat/time congeals and causes sealing problems.

It appears at least 3 out of 4 valve seals have been leaking as it looks wet and shiney.

[steve the grease]

It's quite common for there to be corrosion on the valves/ seats of an engine that hasn't run for ages. Often a good spray of WD40 or similar will clean up the faces of the valves and seats if you turn the engine over for a while, compression magically improves.
____________________
All the above is my personal opinion, you can see my lips move, but I'm talking out of my arse.
I've been riding, and fixing , bikes for 50 years, in that time the more I learn, the less I am absolutely sure of.....

[Robby]

Serious carbon buildup from burning petrol is uncommon these days, you would need to have a bike running very rich across the range of revs/power that it normally sees.

So that looks like oil burning and congealing from leaking stem seals, combined with long periods of inactivity. Worth getting all the valves out for a clean up and new steam seals, you don't want corrosion on the stems ripping up new seals.

[A100man]