How to tell it's time for a valve job...

[Roostabunny]

I recently checked my valve clearances and the guy I traded my one shim with commented that with the size I was trading to (2.60mm) was pretty thin for a GS (mine's an '81 GS850G).

He seemed to think it might be time for a valve job. Now, I didn't ask for his resume, but he owns a motorcycle performance shop and seemed like he'd worked on plenty of GS's - even had a 750 out in the shop - so I thought it was worthwhile to bring the question here and draw on the vast GSR expertise.

I don't know anything about previous or original valve clearance measurements (the PO didn't do his own wrenching) other than that the previous check was over 10,000 miles before the one I just did, and I only needed to change one shim.

I guess my main questions are, aside from thin shims, what are symptoms of needing the valves done and do I need to complete my carb rebuild before I'll be able to tell the difference? Also, it sounds involved and/or costly. How much do I need to save, and are there other big jobs I should plan to do at the same time, like replace my slightly weepy base gasket?

Thanks!

 

[Guest]

If the compression is good and you don't burn oil don't worry about it.

 

[Roostabunny]

If the compression is good and you don't burn oil don't worry about it.

Jeeze you're fast, Chef.

OK, well, I knew I needed to check compression at some point (to get a baseline), and now I know another reason why aside from checking rings/cylinders. Can you tell I'm a newb mechanic?

Oh, and it's not burning oil.

 

[salty_monk]

2.6 is not that thin either... I think you can buy them right down to close to 2.0

Dan

 

[Roostabunny]

2.6 is not that thin either... I think you can buy them right down to close to 2.0

Dan

That was my thought as well - the wrench who traded me seemed to think that they were normally running in the 2.70 to 3.00 range for shims, so he got me thinkin', you know? Just wanted to make sure I wasn't the only one who wasn't concerned. I'll follow Chef's comment, too and check my compression just in case.

 

[TheCafeKid]

2.6 is not thin at all, as stated. I just had to drop a 2.55 and a 2.5 in a motor to get in spec. All the way from 2.80 and 2.75 respectively...yikes, someone neglected some valves...

 

[Nessism]

Both my 550's have mostly origional shims installed and there are a bunch of 2.75's and even some 2.70's. You should be okay.

 

[waltfen]

I am fortunate enough to have a genuine suzuki GS shim set and they range from 2.15 to 3.10

 

[bwringer]

You'll probably have the cylinder head off for some other reason (probably a leaky base gasket/o-rings) long before the valves stop sealing.

With the cylinder head off, there's a spec in the manual for how wide the flat margin at the edge of the valve should be. Once this edge gets sharp, the valves should be replaced.

However, at that point you probably have well over 200,000 miles on the engine and should look around for a lower-mileage replacement engine. They're not too hard to find.

The valves are definitely NOT the weak point of the 850G engine.

In other words, check the valve clearances every 4K miles as specified in the manual, ride the snot out of the thing, and quit worrying about it. :-D

 

[trippivot]

compression check dry then wet-the difference between the two, and leak down test will give you indication if the valves are leaking.

depending on the fuel you use, how you ride the bike, how long the bike is stored every season will determine when you need a valve recutting job. carbon build up could always be a problem cause of valve sealing problems, as can weak valve springs.

a poppet valve can stop sealing for any reason at any time and so can a valve spring loose seat pressure... so do a proper diagnosis test before you listen to any advice.

think of the valve spring that sits for months in a fully compressed position. because at any given time 2 valves are fully squished getting tired. hmmmmm.

 

[tkent02]

Take a look inside the spark plug hole, turn the engine over slowly. You can see the sealing edge of the valve as it opens, there should be a shiny stripe around the head. If it is dull and gray like my exhaust valves, it won't be sealing much.
I think they were ruined by being too tight a long time.

But you need a compression test to know for sure.

 

[Roostabunny]

Waltfen – That’s reassuring if Suzuki issues them that small.

Brian – 200k you think? That certainly puts things in perspective. I’ll tell you what, I’ve been doing a lot less worrying since I replaced my fuel petcock, changed that one shim (reassuring myself in the process that my valve clearances were actually pretty good to begin with), and overhauled/sealed up my airbox. My commuting perma-grin is back.

Trippivot – I don’t actually know that I’m having a valve problem (and it’s an Arizona bike, so no significant off-season), but I put a compression check on the list because it seems wise to get a baseline. That plus my carb rebuild planned for next month should give me the info I need to get that powerplant fully sorted and make it easier to diagnose future issues.