455 bearing clearance??

[DonF]

I'm putting my 455 back together and stumbled upon a new to me olds v8 book by Bill Trovato. In there he talks about the amount of bearing clearance required for the mains and rods in high hp engines, and it's double what the factory calls for. I've had some verification of this on fb but wanted a few more opinions before I tell my machinist to cut my crank at these #'s.

 

[V8 Rumble]

I would talk to your machinist about this I'm sure bearing technology has changed and motor oil tech has changed and those clearances may or may not be the case anymore if it's an old book.

 

[DonF]

I've been doing some reading up on bearing eccentricity and also the reason for the extra clearance. Apparently because of the long stroke of the 455 and the amount of weight the crank throws the crank tends to "flex" especially in high hp engines. I'm looking to be pushing over 500, hopefully midway. Since my machinist doesn't specialize in olds motors I don't expect him to be aware of this idea. Here's a shot of the main bearings I pulled out, now remember these were set up on the loose side.

You can see where the bearing material squeezed out each side of a couple and there was a bunch of bearing material in the bottom of the pan.

 

[1bad79]

that book was just updated this year, the old version is 5 years old give or take the bearing clearance argument isn't a new one at all with an olds,if you go over to real olds power forum and ask this you will get a different answer from almost everyone there best advise is make sure you have picked out a good engine machinist and double check his work. In your area {florida} there is a olds specialist goes by cutlassfi on real olds power you might want to pm him and so him those pics and see what he thinks there are many olds engine guys on that forum but all in different areas with different ideas so do your home work on them {I cant verify any ones work just that he is in your area}

 

[DonF]

Thanks for the info, I'll look into it.

 

[Pontiac455]

Looks to me the bearings were oil starved. You have the upper half of the bearings in the caps. The bearings with the oil holes and groove are supposed to be in the block.

 

[rccktmn2]

Why don't you just call Trovato and ask. He's a pretty nice guy and will answer questions as to why and the reasoning behind it.

 

[DonF]

I tried to email him, no answer. Never saw a phone #, I'll look. Thanks

 

[rccktmn2]

Have you tried Realoldspower.com. He's on there quite a bit and the other guys might be able to help you out. I was never a fan of large bearing clearances even if it's above 500hp but to each their own. Just about any olds engine has a problem with oiling so I don't know why he would recommend a large clearance.

 

[pontiacgp]

the oil these days allows for close tolerance engines. The engine builders I talk to who build race engines use close tolerances because that allows the oil to spread evenly and you don't need as much oil to keep the oil separation between the crank and bearings. Years ago it was more of a gap so the engines would rotate easier