what caused this?

[87-TURBO-T]

I have a low mile (under 10k) SG1 109 short block that wiped the cam. I pulled a couple rod caps off and it looks like the bearings have heat? spots toward the edges.

 

[SS/GN]

Crank not ground proper or too tight clearance.Sorry about your luck

Kevin

 

[87-TURBO-T]

It has never been apart. Is it possible that GM fu**ed up?

 

[SS/GN]

The clearances in a production motor are never perfectThe line bore and crank all have acceptable tolerances,I would not be rebuilding the motor because of that however

Kevin

 

[87-TURBO-T]

The clearances in a production motor are never perfectThe line bore and crank all have acceptable tolerances,I would not be rebuilding the motor because of that however

Kevin

Are you saying you would run it?

 

[SS/GN]

I would measure it first,by the pics those bearings do not look that bad at all.Their is a possibility the cam lobe debris did more to othersKeep us posted to the rest of the bottom end

Kevin

 

[bison]

What do the bearings have for #'s on the back? Post pics of the bearings neAr the parting lines.

 

[steve hughes]

Check the thrust on the crank. It may be walking back and forth.

 

[87-TURBO-T]

Checked the clearences with platigage. .0015 on the mains and .0017-.0018 on the rods. bearing part #'s

rods
GM 4
18001493
36 C 2 1

mains
GM 45
18020192
45 A 4 1

The backsides have black on them too.

 

[RIFF RAFF]

What

Oil you running ? Got zinc?

 

[hansongn]

good point, something as simple as zinc goes a long way and oil is not what it used to be, sorry for your luck

 

[87-TURBO-T]

I have never run the engine, came from a friend.

 

[84BuickGNYorkPA]

When you see copper the bearings are shot, don't look that bad to me, the clearance sounds acceptable also.
Do not mix and match the bearings, they must go back in, where they came out, also do not get the caps out of location or rotation from where they where.

Chuck

 

[87-TURBO-T]

When you see copper the bearings are shot, don't look that bad to me, the clearance sounds acceptable also.
Do not mix and match the bearings, they must go back in, where they came out, also do not get the caps out of location or rotation from where they where.

Chuck

I made sure everything was kept in order. I'll run it and see what happens. thanks for all the replies.

 

[SS/GN]

Oil you running ? Got zinc?

What oil type and weight.Some people run thin 5w/20 and the like,I am not sure it is a good idea.How bad was the cam.Seems odd the cam is chewed and no debris imbedded in the bearings

Kevin

 

[87-TURBO-T]

Not too sure, he just said wiped a lobe.

 

[turbofabricator]

Push the piston/rod up into the bore (or down if the engine is upside down, duh!) and look at the top bearing shell. That is the side that'll show as bad first, as it is the side that takes all the load, unless the ring gaps butt under hard detonation then the lower shell is trying to pull the butted rings down the bore. If the top shell is showing copper, time to replace the bearings. Might be time anyway, as it's aprts and bearings are pretty cheap. Look for crank scoring, too. Might need to polish the crank. It's out, so do it right. Maybe ring time, too.