'70 LS5 - did factory lable connecting rod number?

[Steve G.]

I am in process of frame off restoration of my '70. Chassis is just about done - thanks to all the help I have gotten from this forum!

I am looking to 'freshen up' the engine: hot tank block, re-ring, new bearings, valve job, and paint assuming the machine shop finds no other issues. I was going to number the connecting rods and caps to ensure they all stay as matched sets. I found the numbers are all ready stamped on both rods and caps. Anyone know if the factory did this as standard practice? If not, I assume that means the motor has already been rebuilt. thanks

[Loren L.]

Re: '70 LS5 - did factory lable connecting rod number?

Stamped on the outside edge of the rods? That's a rebuilder trying to put the rod back in the same position. Not a factory stamp.

[Joe L.]

Re: '70 LS5 - did factory lable connecting rod number?

I am in process of frame off restoration of my '70. Chassis is just about done - thanks to all the help I have gotten from this forum!

I am looking to 'freshen up' the engine: hot tank block, re-ring, new bearings, valve job, and paint assuming the machine shop finds no other issues. I was going to number the connecting rods and caps to ensure they all stay as matched sets. I found the numbers are all ready stamped on both rods and caps. Anyone know if the factory did this as standard practice? If not, I assume that means the motor has already been rebuilt. thanks

Steve-----


I've never seen a factory stamping on main caps or rods or rod caps. So, I'd say this engine has been rebuilt previously. A few other "tell-tale" clues:

1) Oversize pistons. Anything other than standard or +0.001 means a previous rebuild;

2) Original pistons for your engine would have a GM casting number on the underside. Of course, original pistons might have been re-used even if the engine was previously rebuilt;

3) Check the rear of the bearings. Original bearings will have a "GM" or "GMM" stamped on the rear of the bearings. Anything other than this means the bearings were replaced. Of course, even if the bearings are stamped as described above, the engine could still have been rebuilt, either using the original bearings or using GM-sourced replacement bearings. Not too likely, though as usually bearings are replaced in any sort of rebuild and GM SERVICE bearings were only sold per each and not per set. The individual GM bearings were so expensive that you could practically buy a set of aftermarket bearings for what a single GM bearing would cost. So, not too many folks used GM bearings at rebuild time.

[Terry M.]

Re: '70 LS5 - did factory lable connecting rod number?

Steve-----
3) Check the rear of the bearings. Original bearings will have a "GM" or "GMM" stamped on the rear of the bearings. Anything other than this means the bearings were replaced. Of course, even if the bearings are stamped as described above, the engine could still have been rebuilt, either using the original bearings or using GM-sourced replacement bearings. Not too likely, though as usually bearings are replaced in any sort of rebuild and GM SERVICE bearings were only sold per each and not per set. The individual GM bearings were so expensive that you could practically buy a set of aftermarket bearings for what a single GM bearing would cost. So, not too many folks used GM bearings at rebuild time.

My experience is that original GM bearings will also have a date code on the back. It has been a while, so I don't recall the format of the code, but it is easy to understand because even as a young whipper-snapper I had that one figured out.

[Steve G.]

Re: '70 LS5 - did factory lable connecting rod number?

Thanks for the replies. I don't have the pistons out yet. I don't see any lip around top edge of the piston bore. And I am now wondering if I should tear it completely down or if there is something I can check to make sure all is in good shape before cleaning it externally, putting new cam and lifters (I see a wear or corrosion mark on bottom of most of the lifterss), reassembling and painting. The car sat and had not been started or moved since the early eighties. Speedometer had been reset to zero, so I do not know how many miles are on it. The previous owner said he had some engine work done on it before he parked it, and reset the speedo. But doesn't remember what exactly was done. I will look for the numbers on bottom side of pistons by looking in from the oil pan side.

Any thoughts as to if there is something I could/should do to determine if I need to spend the $ on freshening? I don't have an inner micrometer to measure the bore width. I'll try to borrow one. Steve