How do valve clearances get tighter?

[LAB3]

Having read through forum postings and this afternoon pulling the valve cover off my GS450t project, my exhaust clearances are too tight to measure. This seems consistent with what I've read but cannot for the life of me figure out WHY. Having looked over the manual and fische pictures, common sense tells me that normal wear and tear should make them looser not tighter. The ONLY thing that makes sense is there must be some erosion or other damage happening at the valve seat. Can someone chime in on this? It's certainly not keeping me from moving forward, just curious.

 

[hillsy]

Having read through forum postings and this afternoon pulling the valve cover off my GS450t project, my exhaust clearances are too tight to measure. This seems consistent with what I've read but cannot for the life of me figure out WHY. Having looked over the manual and fische pictures, common sense tells me that normal wear and tear should make them looser not tighter. The ONLY thing that makes sense is there must be some erosion or other damage happening at the valve seat. Can someone chime in on this? It's certainly not keeping me from moving forward, just curious.

You got it - the valve bashing on the seat over time wears the seat and the valve face so it moves up into the head thus decreasing the clearance to the cam.

 

[LAB3]

Wow, that was quick! The bike only has 7500 miles on it and the gasket looked like a factory job, at least from the outside. Ordered a new one and was thinking what the heck, I might just let this go for now. Glad I didn't! There's a good bit of heat discoloration on the pipes but the plugs looked a bit on the rich side so I wasn't too concerned. Intakes are right in the ballpark at .0025in.

 

[hillsy]

Valves closing up is normal. Make sure the clearances are correct, compression is good and ride. At 7500 miles there should be no need to rebuild as long as there is no damage.

 

[LAB3]

Agreed, I'm a long way from going beyond replacing shims at this point. More than likely I've never come across this before because I never had clearances measure out like this, it's always been the other way around (looser) on my past bikes. Thanks again for the quick reply and insight.

 

[Steve]

Now that you know that clearance gets smaller because of repeated bangings of the valve into the seat, let's play with some numbers.

Let's keep them easy, but close to reasonable. How fast is your engine turning at 60 MPH? I am guessing about 5000 RPM. The engine speed at 60 is also how many times the crank is turning per mile. The valves open every other revolution, so each valve is opening and closing (slamming into the seat) 2500 times every mile. Multiply that by 3000 miles, and you will realize that, during your valve adjustment interval, the valve is going to be hitting its seat 7,500,000 times. Yes, that's seven and a half MILLION times. If you ever use a gear less than sixth, or let the engine idle, that number goes up, so it's not unreasonable to think that the number could easily pass 8 million.

It's actually quite a wonder that the valve adjustment lasts as long as it does. :-\\\

.

 

[limeex2]

Its very normal for valves to tighten up. On intakes, they can exhibit hard starting issues. On exhaust you can burn up valve faces and seats. 4V Honda's are famous for this. Blued pipes can be from running on choke to long.

 

[hillsy]

Tappets can sometimes loosen over time due to the extra mechanical nature of them, but shim and bucket will always close up.

 

[LAB3]

Finally got to removing the old shims this morning, they're both 2.55. Since they're both the same and considering it looks as if the cover has never been off, I'm assuming they're factory installed. Am hoping 2.50 does the trick, the shims are a little under $10 but the shipping is $8 so making swaps could get expensive! Also have a message in to become part of the shim club, what would a customary donation be for that?

 

[Sandy]

The shim club is the way to go. Never used it myself but one thing to try is if you have an older Suzuki dealer nearby a lot of them will just trade you shims or maybe charge a small exchange fee. At least they used to. Bought my own kit years ago.

 

[jsandidge]

Finally got to removing the old shims this morning, they're both 2.55. Since they're both the same and considering it looks as if the cover has never been off, I'm assuming they're factory installed. Am hoping 2.50 does the trick, the shims are a little under $10 but the shipping is $8 so making swaps could get expensive! Also have a message in to become part of the shim club, what would a customary donation be for that?

Be sure not to rotate your motor unless you have a shim in each bucket or you will likely cause damage to a cam lobe. I've used the shim club and it's great. Don't know what's customary, but I believe I donated $5. I've also used a local dealer just last week to swap 2 shims at no charge.

 

[LAB3]

The nearest dealer in about an hour away, it'll be easier to do through the mail for me since I don't currently own a car. This being rural Michigan there's no direct bus service in that direction either.