main and rod bearing clearances
 

was wonder what rod and main bearing clearance to run. i was reading an artice in hot boat a blown 1000hp 572 blower motor built by steve burle he sets his rods and mains up a .0035 which i thought to be too loose. was wondering what clearance you sroker motor guys were running. im going blown 4 5/8 stroke cranks, are blown motors generally set up with looser clearance due to extra heat swelling things in blown app? or do you thnk he's running the clearances taht loose because of the 4.5" stroke of a 572. thx for any insight.

Re: main and rod bearing clearances
 

As a point of reference, the Merc Service Manual for the 800SC (blown 572) gives the following numbers for the rods-.0025 to .003 with rod side clearance at .020 to .026. Mains are .0025 to .003 with #5 (rear) at .0035 to .004. These are production or build numbers. Just trying to help.

Re: main and rod bearing clearances
 

The more power you put the crank the more it will flex. You need more bearing clearance as the crank flexes. More oil cushion for big power also.

There are other considerations.

My typical marine clearances for most everything is .003 mains and .0275 - .003 rods.

Re: main and rod bearing clearances
 

I ran .003 on the mains... .0025 on the rods... some people like a little more clearance on the rear main... up to .0035 I was running 10-4 valvoline at 200 degrees on a 540 blown BBC. No oiling problems after I got rid of the straight 50 weight.

Re: main and rod bearing clearances
 

I like everything at .003.The rear main i make .003 too for good oil pressure.Every motor we build at Zuls is kept between .0027-.0032.

Re: main and rod bearing clearances
 

Ya most like the higher clearance on the blower motors or rpm motors.

Also a blown motor I got from Jim Oddy they put the higher oil pressure spring in the oil pump .They said they found it to give better bearing life ,more cushion?it had 93 psi with 40wt on the Dyno :eek: .I thought this was high but it did not have any bearing problems when I tore it down or and excess windage for all that oil slinging around in there.

Re: main and rod bearing clearances
 

Anybody else have any experience on this ???

Re: main and rod bearing clearances
 

Rob,
Lets See Some Pics Of The Motors :d

Re: main and rod bearing clearances
 

We run the same spec's on all our engines also. If you run the clearances any tighter you need to make sure all the crank journals are round and check the crank run out on the center main. We have seen the run out over .0035- .004 on the center main. So remember that when your UPS driver drops the crank box on the floor.

Re: main and rod bearing clearances
 

i like 2.7 to 3 on the rods and 3 to 3.3 on the crank and i do not open up the rear more then 3.5 always makes good oil presure even after the motor gets hot