valve clearances / compression questions

hey guys. the compression is 150 149 150 150 on my xj 650. is this a pretty good indicator of what the valve clearances are? or is it worth tearing into to check anyways?

 

You must check valves every 5000 miles. It's just the regular scheduled maintenance, no different than changing oil, it's got a service interval that should be followed. It's easy, you'll likely need a new gasket and donuts, and proper feeler gauges. Wait till you see if any are out of spec before buying the removal tool if you want.

Those compression numbers says your engine is VERY healthy. Keep it that way. Valves are closing properly, but they would also if they were slightly out of spec too. You'd still want to keep them in spec, so that they don't go out before the next inspection interval.

 

Solid advice. If YOU'VE never checked them, then you need to. Don't wait until you start having issues; by then it will be too late.

Get 'em in spec, and re-check every 5K. After the first couple of adjustments, you'll likely find that they "settle down" and don't need actual adjusting very often.

But you still gotta check 'em.

 

okay guys thanks for the advice. do the 81 650 motors use doughnuts? the allen head bolts that are in mine dont appear to have any. also they seem relatively stuck. are they notorious for getting seized? do you just use a regualr feeler gauge to check the clearances?

 

Non-yics engines (like yours) do NOT use valve cover bolt "donuts" (and neither does the XJ650 Turbo or XJ1100, even though they are IS yics engines).

Yes, regular feeler gauge to check clearances, although it is very handy to have a set of feeler gauges that are sized in standard metric thicknesses (rather than fractional guages, which although they may have metric conversion markings also, will end up with rather odd metric thicknesses).


Yes, the bolts can be stuck!

 

okay thahks bud. good dill pickle. im putting together a parts list right now for u chacal.

 

I just want to add that by the time a tight valve shows up in the compression numbers you're likely to have big trouble.

 

That's for sure. You check compression at cranking speed so even one with only a sliver of clearance will seat the valve so that you have good compression. All other things being in order that is. Metal expands when heated so as the engine warms you may actually have negative clearance to where the valve is not seating fully. And even if it does seat at low speeds you could still have valve float at high speeds.

When I got my GPz I checked the compression before even putting the carbs on. I had 180-185 all the way across, which told me the engine was still in like new condition as serviceable limits are 120-190 on that bike. However when I checked the valves every single one was tight and a couple were almost at zero. The bike had 10,000 miles on it and it was obvious that the oil was probably changed regular but the valves were never touched.

I only checked two holes on the maxim because I was getting a bad miss, which later turned out to be a couple bad spark plugs. I checked the two outer ones and both were 155 which I thought was very good considering the bike has 34,000 miles on it.

 

Good to know. And yeah I didn't even think about it being out of spec causing them to float just not seat properly.. ohh valve train here I come. Lol hopefully ill be lucky n wontbhave to buy any shims lol . Wishful thinking.