455 bearing clearance??

[Bonnewagon]

Why go with big clearances unless you are racing? That will only bleed off oil pressure, which you will try and recoup with a high pressure pump and thick oil. Hard to tell with the glare but it looks like they all starved for oil except for the ones with the groove which makes sure oil gets to the entire length of the bearing. I like fully grooved bearings for everything as it assures full bearing oiling but the downside is it reduces total bearing surface. Teardropped oil feed holes in the crank and opening up all oil holes help a lot to and I feel a high volume oil pump is mandatory anyway in any high power motor. Did you read up on Joe Mondello? http://www.mondellotwister.com/articles.html

 

[Rktpwrd]

As stated before, Olds engines and 455's in particular have weak oiling systems. Attention given to a few key areas will help with the longevity of your motor.

First, get yourself a good quality Melling high volume oil pump, (not high pressure), and run a thicker oil to maintain oil pressure. As you found out the hard way, 455 cranks will walk around a bit, so slightly larger than normal clearances are required. Forget tighter clearances as others might suggest, this is an Olds and not a small block Chevy. To help minimize crankshaft walk and flex, upgraded main caps and/or supports are a very good idea. Also, use main cap studs, preferably ARP, and not bolts.

Further, installing oil restrictors (available from Mondello racing) under the main bearings in the block to cut down on the amount of oil directed to the top end will keep it down in the mains and rods where it's needed.
The fact that it spun the main bearings and not the rod bearings tells me the crankshaft was flexing under load. That combined with tight clearances is likely what lead to the failure.

And possibly most important, keep your rpm's down. 5500-6000 rpm MAX. 455's don't like high rpm's, they're torque monsters. And quite frankly, with torque numbers in the 500 ft lb range from almost idle on up, you don't need big rpm.

These suggestions combined with the other standard performance engine building practices mentioned above (chamfering oil holes in bearings etc) will help ensure your rebuilt 455 is a happy one.

 

[online170]

As Rktpwrd said, go loose, not tight. Its a big journal olds! Oil must be matched to the clearances.

A good rule of thumb for performance builds from the pre 90's era is 0.001 for 1" of journal diameter. You can go big on the main bore, and small on the main journal, and you still wont achieve this rule of thumb (it will be too tight still). If you want to stay conservative, use this big/small method from the factory spec. That way you are still within factory specifications. I think you will get to 0.0025" clearance.

Otherwise, to get the .001" for 1" of journal diameter, you need 0.003" of clearance for the 3" journal. Measure/hone the main bore as required, torque up the main caps with bearings, measure the main bore, and calculate what you need the crank size to be. Usually crank grinders will do this for you.


In 1970 when the 455 was putting around at 3000rpm, the factory spec was fine. But the factory spec is REALLY REALLY tight! It allows for 0.0003" to be acceptable. Think about that! 3/10ths of a thou. I wouldnt run 500hp and probably 570ish torque on that.


Now as for your bearings, you cant blame that failure entirely on clearances. Some of the bearings still look OK. Olds have a starvation issue, and you havent mentioned what sort of RPM you were pushing and for how long, or the oil you used. You need to restrict the top end of oil flow, have adequate oil capacity, and proper running clearance.

 

[DonF]

Thanks for the responses guys. I've been reading Mondello's articles and a couple others since the mid 90's and I finally put this motor together in 07'. It was a long time coming and all the little things were done, elongating oil drain backs, cross drilling crank, chamfering, etc. etc. etc. The bearings are actually the Childs & Albert bearings he sold, I have seen they are now no longer in business, and are full groove except for #1(which never is). I did have one of his blueprinted pumps in the motor, and everything was fine breaking in the cam(I'm going to reinstall a Melling HV). The first night I decided to actually take her out, I saw oil pressure was getting low(this was the first time it ever went below 50psi). Here's the screwy thing, the car would fire up with 60-70 psi oil pressure then as the motor warmed up you could watch the pressure get lower. Now this was 8+ yrs ago so if I remember right even if the rpms were increased the pressure never increased. The pressure would usually bottom out around 25psi every time I checked the next component in a search for the easy fix first. After 8+ yrs I finally pulled it end of Sept. and this is what I found, which led me to Bills book and a few new ideas on clearances I had never heard about. I need to check my rod side to side clearance now and I guess that will determine if my main/rod clearances.
Does it matter in my side clearance that I have the .500" wide grooves in the big end that Mondello used to recommend? I'm trying to get on over at Bill's forum so I can get in touch with him.