Topic: Ok to clean pistons while they're in the cylinders?

[PBZ]

So I pulled the head off my 350F today in order to replace the head gasket since it was leaking a little oil around there. Once I had the head off I noticed a decent amount of carbon build-up on the tops of the pistons.

I read elsewhere on the forums that permatex gasket remover works good for removing this, but I was wondering whether it was a bad idea, since I imagine at least a little of this stuff will find its way past the piston rings and into the crankcase. Maybe just change the oil when I'm done?

Or should I just leave it, fix the likely carburation issues and let it burn off?

Also while I've got it this far apart, is there anything else I should do to it other than replacing gaskets and seals?

Thanks,
Jason

[bucky katt]

no

[Gordon]

By removing the head you've likely broken the seal of the cylinder base gasket, so you should really go ahead and remove the cylinder block to replace that gasket anyway. 

[camelman]

I agree with Gordon.

Lap your valves while you are at it.  It is pretty easy, and you need to take the retainers out to replace your valve seals anyway.

You can clean your pistons when you have the cylinders off.

Camelman

[PBZ]

Well I took Gordon's advice and popped off the cylinder since I definitely broke the seal (forgot some cylinder head bolts, oops). Got all 4 pistons cleaned up and reinstalled already. I'll get to the "fun" job of removing all the old gasket material tomorrow.

Any tips on putting the cylinder back on? I've never done this before. I was thinking some pieces of wire bent into an appropriate shape could substitute for the special "base" tool in the manual and some hose clamps for the piston ring compressors.

Lap the valves huh? I'll have to think that one over. Trying to get this thing back together ASAP so I can ride it! The season isn't that long here, and this time of year could weather is hit or miss so you've got to take it when you can get it. I just sort of tore into this thing on an impulse and the leak wasn't really that bad, but it was bugging me so here I am. Overall not hard at all, I love working on bikes, so much easier than cars.

[PBZ]

Well I took everyone's advise and lapped the valves, and then prussian blued them to check. They weren't terrible to begin with, but they're much better now.

The cylinder block went on with out too much trouble with some helpful tips found on the forum: did 2 cylinders at a time and didn't use any ring compressors. Not bad at all, just took a little patience.

So now for the question: everything's assembled and torqued, tappets are adjusted. I was going to do a leak down test but didn't have a tester or the parts and didn't feel like running out so I decided just to do a compression test. I wanted to do this all before the bike was fired up and all the gaskets "became one with" all the metal parts, just in case I had to tear it back down. Here are my results, what does everyone think? 99% sure it doesn't matter but just in case I'll mention that I did this with the carbs and exhaust off (shouldn't make a difference). And again the engine has not been run at all since I had it apart, just cranked over a few times, and I did have a thin coat of oil on the cylinder walls when assembling.

1: 135 psi
2: 132.5 psi
3: 127.5 psi
4: 140 psi

That makes the largest difference between cylinders 9% or 10% (depending on how you calculate it) which is right at the max discrepancy my Clymers manual recommends. Are these results even meaningful at this point? Should I perform a leakdown test?

When I added some oil into cylinder 3 the reading jumped WAY up to 230psi

[dave500]

the test must be done with a hot engine and the throttle wide open.

[bucky katt]

compression can be manipulated with valve adjustments too, you want more static compression you put a little more clearance into that cylinders valve clearances