1978 gs 1000c pistons/rings

[Coldeye_]

I am interested in rebuilding my 1978 gs 1000c engine w/ 25k or so. It was brought back to life, but I discovered the #1 cylinder seems to be down. Either a bad valve guide, burnt valve or piston rings. Have done the oil test in #1 cylinder and raised it the compression the compression from 65 to 95-105lbs. 2 3 4 cylinders are at 155 give or take 5 lbs. Bike runs decent w/a b7es, but I dislike the popping noise I cannot tune out and I know the motor has more to give, just sick at the moment. plug is very oily and sutty. I'm thinking rings. Valves have been properly shimmed to spec, test was done warm WOT. The carbs are brand new cr kehiens, new dyna ignition-coils timed correctly.

The real question is, can anyone recommend a good place to buy pistons, rings, gaskets and other parts to do the valve train?

I searched the Z1 site as I have used them in the past and am very impressed w/ their service. May also be looking for a machine shop in the Orange County, Ca area or close by. Interested in costs, dos and don'ts from those who have gone before me or in the process of the same task. I have read and searched the forum and I believe I might be up next for the step by step thread.

Please send help!

 

[Big T]

At 25k, the pistons should still be good unless they suffered some damage. More likely stuck rings in #1.
Have you tried some PB Blaster,or Seafoam in #1 to see if the compression will increase?

Don't rush into buying pistons. First, take the top end off the motor and measure the bores, pistons, end ring gap, etc to see what the problem is. You need to check the valves. also.

You may only need some new rings and a honing.

Pistons are available from the dealer, and the Wiseco 1085 kit is a popular (and probably cheaper @ $580) alternative.

A rebore and valve job will set you back $800-$1,000, depending on who does the work

 

[robertob]

How many miles do you have on it since you started it?

Mine sat for 26 years and it was down on compression in one cylinder. I rode it anyways and got it good and hot a couple of times and now compression is 145 across the board.

I soaked the cylinders in ATF before I ran it, though. You might try something similar.

Don't tear it apart unless you get some serious miles on it.

 

[robertob]

Also plugs should be b8es, not 7.

And valve guide will not cause low compression.

If you did the oil test then you ruled out a burnt valve.

The only possible problem is ring seal.

Also, how do you know your carbs are set up right at low speeds? That would cause the plug fouling you talk about too.

 

[Coldeye_]

Thanks for the input. I'm still fiquiring a prob. w/ the piston rings in #1. Carbs where set up by Sudco when I purchsed them new. They could be a prob, but still wouldn't bring the compression down. It really is an oil soot and not fuel on the plug anyways, at least by smell. I will try a nice ride this weekend and see what happens. It runs decent like I said, just pops when idling as the cylinder seems to load up and seems down on power. Bike was sitting a while before I got to it. Still, where are you guys getting your parts from? I know it's not suzuki unless your have money to burn.

Thanks again!

 

[hp1000s]

.......check valve adjustments? Tight valve clearance can cause popping & lower compression.

 

[doctorgonzo]

"Also plugs should be b8es, not 7"

The B7ES is the hotter, and the B9ES is the colder. I run the 7.