GS850 - serious noises

[Anonymous]

HELP!!!! I have re-ringed my 79 850. With 73000 KM's (approx 45000 mi.) the dealer honed the block only. I used std. rings on the original pistons. All dimensions are within limits per my factory (pink cover) manual Upon re-assembly a loud knocking, hammering sound started after about 15 minutes of running. I took a 20 min. ride to the dealer for a second opinion, as well as going through your entire tech.section. He suggested the cam chain tensioner, as many others did. Went through it thoroughly even though it appeared to be operating OK. Still noisy and getting worse. Pull the plug wire on #4 and noise is 90% gone. Stethoscope confirms noise is loudest in upper area of #4 cyl. I dis-assembled and pulled the cyl. block as well as #4piston. Everything is visually OK, all dimensions and clearances still within limits. If anything, wrist pin and pin bores are on tight side. Big end side clearance is .019''. No broken rings or scuff marks. And compression is an even 125 all round , which should be OK since the rings haven't seated yet. I have another piston which I am about to try but I'd rather pick the collective brain before re-assembly. I did find a slightly warped compression ring on #3 piston , could this have anything to do with the noise? (I will be swapping this ring out in any case) hoyterb's comments noted and I verified that the pistons are all installed with the cast-in arrow pointing forward. ,Any more ideas? How can I check for main bearing damage without removing the crank?
Thanks all

[hoyterb]

Did you put the piston in the bore backwards.I'm serious.The piston may be offset and is now cocking in the bore too much and banging when it fires.Thats why it goes away when you pull the plug wire off.ALL High perf. pistons I have used in my Chev SB engines are offset pins.It helps them rev higher without breaking the piston skirts.
Good Luck

[Anonymous]

hoyterb may have your answer right there. I am not sure if your GS has offset pistons, but I do know from experience with other engines that if you put a piston in backwards some will not run at all!

I even know from my college days working in a small engine shop that if the pin holding the piston head is put in "backwards" it can seriously affect the engine.

[Anonymous]

GS850 - serious noises

Did you put the piston in the bore backwards.I'm serious.The piston may be offset and is now cocking in the bore too much and banging when it fires.Thats why it goes away when you pull the plug wire off.ALL High perf. pistons I have used in my Chev SB engines are offset pins.It helps them rev higher without breaking the piston skirts.
Good Luck

hoyterb tks. for the speedy reply. No offset on these, plus they are marked with a cast-in arrow on the crown so I am sure that isn't the problem.