Dirty pistons/valves... next step?

[Ions001]

Howdy all!

After a year long wait, I've finally had the time to tear down the engine on my 1980 GS1000 to see why cylinder #4 only had a compression reading of 30.

The tops of all of the pistons are covered in a black crusty substance. The inside of the head has the same. The fourth cylinder is the worst of all. I've places some pictures in the following album:

http://s17.photobucket.com/albums/b52/Ions001/Engine%20Rebuild/

This is by far the biggest mechanical issue I've ever tried to fix. I've got my Clymers book in hand and so far so good.

I'm thinking that I need to replace the rings, clean off the pistons, and take the head to a machine shop for cleaning along with a valve job.

I hope I'm providing enough info, but does this sound like a correct course of action?

[salty_monk]

Did you work out the cause of the low compression? Was it recessed or non seating valves or rings or something else (maybe a crack?) that would be the first job.

You can probably clean it all up regrind the valves & put new rings on yourself (or at least you could with a car.... not much experience with bikes).

Do these engines have stem seals? If so they would be worth checking too.

Also low compression could be simply a case of really bad valve adjustment, I take it you checked before you tore it apart??

Dan

[Ions001]

Wow... thanks for such a speedy reply!

Did you work out the cause of the low compression? Was it recessed or non seating valves or rings or something else (maybe a crack?) that would be the first job.

I've inspected it quite closely, and didn't see any cracks. The build-up on the valves on cylinder #4 prevent the valve from closing. Cylinder #3 was getting close to that point, but not quite.

You can probably clean it all up regrind the valves & put new rings on yourself (or at least you could with a car.... not much experience with bikes).

The rings I could probably handle, but I get nervous when I hear the term 'grind'. I may be better off letting someone with more experience do that part.

Do these engines have stem seals? If so they would be worth checking too.

Also low compression could be simply a case of really bad valve adjustment, I take it you checked before you tore it apart??

I'm not sure what a stem seal is. I'll have to do some investigation. As for checking the valve adjustment, no I did not. I'll have to do some further reading so I can go about things in a more logical order in the future.

Thanks again for the reply.

[robertbarr]

With a reading as low as 30 p.s.i., I'd expect to see some visible mechanical damage somewhere -- a chipped valve, maybe, or a split seat -- but as stated earlier, really tight valves could do that too I suppose. I don't see any obvious escape path along the gasket surface.

If you haven't shuffled the shims, you should be able to bolt the cams back into place and get a reasonable measurement. At the very least, it would be a quick way to check for zero (negative, actually) clearance on that dud cylinder.

You might not need to grind the valve faces. Unless they're worn, you can get away with lapping them. The bonus is lapping won't throw your clearances low like grinding will, and it's cheaper to boot. (DIY = almost free!)

You'll want to clean up the stems & passages and replace the stem seals, though, so it's time to hunt down a valve spring compressor.

[bwringer]

A Vesrah gasket kit comes with the valve stem seals along with all the other gaskets needed for a top end disassembly.

These are fairly simple engines. Relax, take your time, and you can do a great job the first time.

[SqDancerLynn1]

If I were you send it to http://www.aperaceparts.com/headwork.html

[mark]

Take your block in as well to make sure its in good condition, flat, etc. Check for nasty scratches on the cyliner walls(ask me how I know). If you're doing the top, then you should do at least rings and a hone job on the bottom. Check your cam chain to make sure its within spec. as well.

[49er]

The pic showing your #4 chamber and ports depicts a high carbon buildup on the valves and the exhaust port. This indicates that the engine has very high mileage and /or bad oil bypass at the rings. For carbon to build up so badly on the seating part of the valve, someone has probably been running the engine with no exhaust valve clearance on that pot for a considerable period of time. Sounds like other valves were tight too.
You may need more than new rings for this engine.

[ron bayless]

If I were you send it to http://www.aperaceparts.com/headwork.html

WHERE DO YOU GUYS GET ALL THESE GREAT SITES?I HAVE OWNED MY GS 1000 FOR ABOUT 18 MONTHS,NOT UNTIL I CAME TO THIS SITE DID I FIND SO MUCH INORMATION.ONE QUESTION--I read so many times how bulletproof these roller bearing engines are supposed to be.Yet mine and many others here are requiring extensive repairs or rebuilds with relatively low mileage.why is that? is it because bulletproof is a relative term? i suspect car engines that make peak torque and horsepower as well as most cruisers do at about 2500 rpm compared to our bikes making their peaks at about 6000 rpm is one reason for prematurely wearing out of the engines.?

[robertbarr]

-I read so many times how bulletproof these roller bearing engines are supposed to be.Yet mine and many others here are requiring extensive repairs or rebuilds with relatively low mileage.?

You're not having any bottom end problems... and if valve clearances aren't adequate, it sets off a snowball effect of accelerated wear, due mainly to heat.

You'll see plenty of hard-ridden GS's with 70k and more. My 850 ran perfectly at 54k when I sold it, and I beat the #@$%# out of that bike on a daily basis, but it got the maintenance that it needed.

[ron bayless]

You're not having any bottom end problems... and if valve clearances aren't adequate, it sets off a snowball effect of accelerated wear, due mainly to heat.

You'll see plenty of hard-ridden GS's with 70k and more. My 850 ran perfectly at 54k when I sold it, and I beat the #@$%# out of that bike on a daily basis, but it got the maintenance that it needed.

That is why i like my bike so much.I can do lightning fast acceleration anytime i want and the bike is phenomenal.Plus even though i think it needs a 6th gear,it can cruise at 70,80,90,whatever and pass people going UPHILL.I didnt realize upper end problems are not considered real problems.I would agree they are minor in comprison to spinning a main,throwing a rod,etc.I am learning.Ron