Pulling my head off.

[GLoweVA]

Doing some pricing on ring sets, I might just do the one piston fix.
Just one set of new 1up rings is about $20. (times 4 and that's $80) not to mention the price of the replacement piston.
Then, If I want to replace the jugs too and 3 more pistons!
Ouch! $$$$
I suppose that if numbers 1 thru 3 are good, why mess with them.

[crazy steve]

Doing some pricing on ring sets, I might just do the one piston fix.....
...I suppose that if numbers 1 thru 3 are good, why mess with them.

The problem with only doing one is you may end up with one cylinder with great compression and three that are only 'ok'. What's the numbers on the other three? If their good and high, you may be able to get away with it, but otherwise you may end up with too much of a 'spread'. All cylinders should be within 10% of each other for a smooth running motor, the closer the better...

[GLoweVA]

I got #1: 150, #2: 140, #3: 135, and of course #4: 30 (with the carbs off)
So, If I can get #4 anywhere between 150-135, that should be good to go.

I'm thinking that since I have the head off, now would be the best (and easiest) time to swap out a few of my valve shims. (i've got a few that are just below spec.)
If I swap out the shims, wouldn't that make my compression go up just a little?
(intake valves shutting sooner and exhaust opening later)
(I know I'm talking miniscule amounts of time, but any little bit would help)

[crazy steve]

I got #1: 150, #2: 140, #3: 135, and of course #4: 30 (with the carbs off)
So, If I can get #4 anywhere between 150-135, that should be good to go.

You're already at the recommended 10% max variation (between 1 and 3), and while those numbers are 'acceptable', they're also low. A new ring set should give you numbers in the 180+ range, which will put you at between 20% and 30% at least; this big of a difference will give a noticeably rough-running motor. What I've typically seen on 'good' motors with good ring seal is numbers in the 185-195 range. I'm not aware of a way to 'fit' rings to reduce this without risking damage or faster wear down the road.

You really should replace all the rings, or go with a good used 'matched set' of pistons/cylinder...

[GLoweVA]

Thanks Steve.
Even though it'll cost me more money, I have to agree the best option is to go with 4 used pistons (with matching jug) and new rings on all 4. (except oil ring which i've read you can't fit the new oversized one on to the 71.5 piston)
At least this way the 'new' jug will clean up real nice before I put it on.
I got my hands on a honing stone rig from a friend, so I can deglaze the jug before I put everything together.

This whole experience has taught me to make sure my carbs are balanced and sync'd. Had they been, I might not have burnt a hole in one running too lean.

ps. Anyone got lying around a jug and set of pistons just taking up space?

[natemoen]

You can usually find jug and piston sets on ebay from $35 on up.

[crazy steve]

If you're going to do new rings, you don't need the replace the other pistons or cylinder unless the bore is damaged. Get another piston, and just replace the rings.... should save you a few bucks...

There's 'standard bore' ring sets on eBay right now for $85.

[GLoweVA]

Yeah I saw that ring set for $85, ouch!
I think I'm going to get just one newish piston and a ring set, since my jugs are in decent shape.
There aren't any broken fins or other damage.
Of course I won't know for sure until I pull them off and check the cylinder walls, but with the previous good compression numbers, I feel fairly confident that they'll check out ok.

On a different note, I was thinking that when I pull the shims off to figure out which ones I have, I can maybe rearrange them (ie. swap them around) to adjust my clearances. I did do some measurements last month so I know what I've got, now I've got to figure out which shims can go where to make my numbers in spec and if I need to get any new ones.

Are the pistons ferrous? I'm asking because once I pull the bad one off, can I go into the hole with a magnet and 'fish' for any small pieces that might have been created during the burning of the hole. Not that I expect to find any, but it'll be nice to be sure. Splitting the case is not something I feel confident to do just yet. I know that one day I probably will have to in order to fix the 2nd gear issue, but so far my bike has been pretty good about that.

She's supposed to be my daily driver and I want to get her back on the road asap. (the gas mileage in my Jeep is eating up all my money ! )

[crazy steve]

...On a different note, I was thinking that when I pull the shims off to figure out which ones I have, I can maybe rearrange them (ie. swap them around) to adjust my clearances. I did do some measurements last month so I know what I've got, now I've got to figure out which shims can go where to make my numbers in spec and if I need to get any new ones.

Are the pistons ferrous? I'm asking because once I pull the bad one off, can I go into the hole with a magnet and 'fish' for any small pieces that might have been created during the burning of the hole.

Yep, you can move the shims around; that's what I did on my SG and I only needed to get two shims to adjust the valves. I'm sure you'll need one or two, but that's better than eight.

The pistons are aluminum, so no help there...