I had my main bearings spin inside the 3 inside caps. most of the wear was concentrated on the caps, but some was evident on the block. I came across these in the Jegs catalog:

http://www.jegs.com//cgi-bin/ncommer...92&prmenbr=361

And was wondering if it were possible to have a 350 block and caps line bored for 400 main's and snap these spacers into the new journal size. I've obviously never done such a thing, but it would save me a ton of money as I already have alot of machining done to this block. I know your loosing some strength doing this, but what diameter are 400 mains compared to the 350? Do you think that the water jackets will be hit doing a bore of this size?

Thanks

Bill

 

Why did the bearings spin? You need to figure that out before trying any corrections. How much hp are you pushing thru it? What rpm? 4-bolt? iron or steel caps? More information on your engine would be helpful.

Using spacers will weaken your lower end. I suggest you not try it. It will cost a lot to align bore that much out and then align hone. I don't think it will solve your problem, and if may make it worse.

 

You only want to use spacers when there is no other alternative.
Some have used them with good luck,more have had not so good luck.
Chevys are not bad to have a main brg problem,soooo might want to get some expert advice on the cause. Take it to someone that knows about these things and let them put a good eye on it and give there opinion.

 

It appears the bearings were to wide and not chamfered enough and seized to the crank itself and then the bearings themselves were spinning with the crank in the caps. If I don't do this alternative, the block is a boat anchor, there is nothing else that could be done besides machining the lower side of the block, reregistering the caps and line boring it again, and there is no garantee that that can even be done. Then problems can arise with slack in the timing chain, and I'm not aware of any incrementally shorter chain available for a roller cam block. Engine was a LT1 block with an Eagle 3.48 stroke forged crank and 4 bolt nodular iron main cap conversion. was only running 7 psi 6K rpm and probably not over 500 Hp. Motor lasted only 500 miles or so and was not really abused, just street driven, mostly highway. I have already been advised next time I'm assembling to carefully watch bearing width and make sure there is proper chamfering to clear filets in the crank and rod journals, I think that was my assembley mistake. I will try a narrower race bearing next time.

I already picked up a new block which is being hot tanked right now, I just ran across the spacers and thought it may be a viable alternative to junking the block. Yes it will be a larger align bore, but I don't think it would be much more than what they did with the original align bore of the new caps. There was alot of material that needed to be removed from them.

 

There really is no other alternative other than scrapping the block and start new, but like I said it would be a shame to do that. Machine work isn't cheap! But if that is whats best I will do it.

 

That would be the best with that kind of damage. You can get it line bored and go back original or I have a virgin 4 bolt, vette, LT-1 block if you want it. It has never had a piston in it. It has surface rust and would have to be cleaned thoroughly and checked.

 

I was just talking with my machinist about this the other day.
Actually, we were talking about boring the main saddle of a 350 to take a stock 400 crank. There's 0.100" that has to come out on the radius. It looks like it would be ok in the block, but the main caps would then become the weakest link in the system. You just know that Chevrolet didn't put any more material in them than was absolutely necessary. One thought was to polish and double shot-peen them. Might work, might not. Untrodden ground. The larger bore may or may not cut into the cap bolt holes. If if weren't large enough to restrict movement of the bolts in and out of the saddle against the backside of the bearing, it might be ok. New bearing tang slots would have to be cut into the block and caps. I'm told these are not critical as long as they're close. Cut 'em back in with a hand-held die grinder mounting a 2" abrasive cut-off wheel. At the end of the conversation, we concluded that we'd only do this as a last resort and that it would be a better idea to use a Scat crank.

 

I had a main bearing spin this year. It scored the crank but I was able to get it repaired. It also toasted the bearing cap by warping it. It was warped enough that it moved around on the register. The machine shop suppiled me with a new bearing cap and line honed the block again.

 

Sure wish I would have known this about 2 weeks ago, I already purchased a LT1 core and new steel main caps Would have went this route, I searched ebay and the For Sale section, but there were none

 

Specifically, what bearing, that would have been too wide, was originally used? Or, did it just have an incorrect/incompatible chamfer, for the crank fillet? ....Bummer.

 

Yeah, incorrect chamfer looks to be the problem.

 

This should have been caught when crank end play was checked. If the chamfer was wrong,then the end play was "0". You might not have enough clearance on the size also..0027-.003 is needed

 

Yep you are 100% correct. never enough time to do it right the first time, but always enough time to do it over. didn't have the dial at hand, was at work, and wanted to get it done as I had limited time. I guess I will chalk this up as a learning experience, a very expensive one that will not be repeated!