Currently inspecting my 350 TPI. I opened it to replace gaskets and have a look while I am at it. So far I ordered a new set of GM stamped steel rockers as the ones that I had were not all the same. Will also change some sensors and also putting in a double roller cloyes timing set.

I also had what looked like the very early beginning of compression leak between 3&5 so I filled in the light scratch on the head and block and re-faced the decks.

Grinded the valve seatings. Pistons are 0.060 oversize, pistons have a small dish, bores are still very nice, camshaft is almost perfect ( very slight pitting in one lobe). Crankshaft has been turned as the bearings are 0.010 oversized but again condition is very good.

No form of loose in the main bearings BUT normally main bearings are a bit hard to put in the connecting rod journals. At least that is my experience in other engines but on this one none of them are. All fit perfectly but they are easy to put on. Not even the ones on the main journals (ie not just the ones on the crank).

Is this normal? Bearings seem to have been changed recently as they are almost new. No scratches or nothing. Just I am used that normally bearings are a bit less curved than the journals resulting in a tighter fit.

 

I'd recommend getting new bearings sense your in there.... both mains and rods. But if you have no way to measure the clearances it can be tough. Some ppl use plasti gauge but in my experience with it it can be way off. A micrometer and dial bore gauge is best. I'm sure you could have a machine shop check it for you for fairly cheep. Even finding a vocational school that has a engine building program may help ya out. You can try plasti gauge just to get a rough estimate but I'e found it to be .003 off, which is about the max tolerance youd want.

I have found sometimes bearing halfs dont always push in or seat tight like others do. Just make sure that when you slide the halfs in they dont score on the corner/edge of the journal.

 

In my case none of the bearing halfs fit in tight that's why I thought maybe this is how sbc should be. Mind you the engine didn't have any noise. As I said I opened it mainly to replace gaskets and seals.

If I manage to get a micrometer and dial bore gauge, what should I be looking at?

Don't have much experience on this subject.

 

Using plastigage, 0.002-0.003" is typical for bearing clearance. I wouldn't want them any tighter than 0.0015 in a street engine.

Too tight and you risk burning up a bearing. Too loose and oil pressure suffers.

If you don't have the proper tools or experience, it can be a lot cheaper to have a machine shop put the bottom end together and hand you back a complete short block. Let them do all the measurements and assembly right the first time. A properly built engine is assembled and disassembled a few times to make sure everything fits properly.

Slapping a bunch of parts together and hoping it will stay together for a long time is a waste of money. If you're going to do that, just buy a new replacement engine.

 

what I meant was, if your clearances are already .0025 or what ever and the plasti is off by .003, .0055 is way too much in my book. No good machinist or engine builder relies on that crap. If they have it in their shop its used as a book marker....

 

What you're seeing is normal. It's normal for the bearings that have already been installed (used) to fit into the bearing bores "loose" (this is not the correct term, but we all know what we're taking about here) when compared to new, out-of-the-box bearings.

This is because new bearings are made to "crush" in their bores when installed (the two halves are not perfectly round, as you noted). This is what's supposed to hold them in place.

 

Ahh that's some releiving news. Honestly I wasn't going to change them as as I said there were no problems with the engine and thought as the bearings and crank do not have any scratches and they have bedded together why change them. As long as I keep the same placement I should be fine. I also avoid having to polish the crank in vain.

Am I reasoning correctly?

 

IMO, I wouldn't do anything to the bearing surfaces on the crankshaft or bearings (polishing) other than to make sure they are free and clean of any debris before putting it back together.

It's too late, but I wouldn't have removed the bearings from the connecting rods/caps or block/caps. You have already removed them so yes, make sure they go back in the same place they were removed from.

It might not be a bad idea to smear some assembly lube on the bearings and bearing surfaces before re-assembly.

What Alky suggests is a good route to go. However, beware that once measurements are taken, you might be looking at a complete bottom end.

You're in this project pretty deep already. It's probably not worth just slapping the bottom end back together, considering you have already gone through the trouble of getting the heads done.

 

I will see if I can get a dial bore and micrometer from a friend of mine and measure the clearance between the crank and bearings. If I don't manage I am not going to go ahead troubleshooting a non existing problem. I will carefully reassemble everything cleaned and where it was and see how it goes.

 

Plastigauge if its new is pretty accurate. Its been used for years by engine builders all over its not going to be off .003

Its pretty simple how wax piece of string works !!! I have had many guys I that I machine there blocks and size there connecting rods and set there bearing clearances with my Sunnen gauge and when they are assembling there engine they have checked it with plastigauge and they seem to be pretty dam close to what I came up with. They were not off .003 LOL

If your using a cheap bore gauge with rigid fingers and not a Sunnen bore gauge with floating fingers.

When your measuring bearings with eccentricity Sunnen bore gauges are the only way to go. I have seen many guys bring the 100.00 Met bore gauges in and check it against my Sunnen gauge not even close.

Plastigauge from what I have seen is more accurate then some of the junk bores gauges out there !!!!!!

Here is a good thread to look over you need the right tools to do the job correctly.

http://www.performanceboats.com/gn7-...learances.html