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Discussion Starter #1
ok .. a buddy of mine has this gm perf parts 502/502,alum heads hyd roller,tuned port efi crate motor in his 25 baja outlaw. i am asuming that all the engine are speced out for passenger car service,so the tollerances are tighter than on marine,he siad his oil press was at 90 psi on cold start,due to tight tolerances,what should specs be for marine application? rods,mains,pistons,rings ect.
 

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Re: marine tolerances?

torino501 said:
ok .. a buddy of mine has this gm perf parts ...crate motor in his 25 baja outlaw. i am asuming that all the engine are speced out for passenger car service,so the tollerances are tighter than on marine,he siad his oil press was at 90 psi on cold start,due to tight tolerances,what should specs be for marine application? rods,mains,pistons,rings ect.
The difference in marine application engines is moreso in the piston-to-cylinder wall and not necessarily the bearings (which would indeed affect oil pressure). Pistons are usually fit .001"-.003" looser in a marine application than than in passenger car; this is because the marine engines typically run at a higher sustained rpm, which creates more friction and thermal expansion of the piston. Further, in marine-application open cooling systems, the block will not get as hot as in a closed cooling system such as found in a car, and so the block/bores do not expand as much, hence the looser piston-to-bore clearance again.

Bearing clearances are not quite as picky in this application specifically and would essentially be no different than any other engine running 5000 rpm sustained...which I doubt the 502 crate motor is clearanced tot do..

Paul
 

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If I were guessing would say the 502 performance marine and 502 crate motor would be one in the same as far as clearances go, with different cam and induction system.

.002 on rods and .003 on mains should be adequate for the 5000 rpm deal.

JMHO! Bret
 

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Discussion Starter #5
well i pulled the oil filter on his boat,(what a pain)dude that installed the engine whahued the remote filter.cut the filter open and bearing crap everywhere. the oil did seem a little thick to me. goober(my buddy) said when he first got the engineit had 90 psi of oil press,he said every time he took it out the oil press would slowly get lower and lower,this engine had real low hours on it ,maybe 20-30 at the most. he bought the boat 2yrs ago from a guy in some brac water,i was going to go with him but couldnt get away,well he brings it home.my god what a mess,the anoid tabs lookes like swiss cheese,the head bolts were just buttons,motor and out drive shot to total hell,this boat nickled and dimed him to death,he put the zz502 last year,he's had well .....idiots butchering up his boat,out drive out repaired twice,power steering leaks,ive been to busy working on my own FORD hotrods to work on chevy,besides my boat runs fine.speking of my boat my baja has the 502mpi,has 40 psi of oil press at idle cold,25 hot and 50 psi 5000rpm hot with 20/50 .
 

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Discussion Starter #7
well we pulled the gm perf ZZ502/502 out,spun 3 rod bearings,stacked one of them,2 rods pretty much wasted,all mains were ok,for grins i ck the clearances with some plastigage,i cleaned all the oil off the bearing shells and on the block/caps and rod/caps torqued them down, dude ive never seen green gage get so damn wide.it was atleast .001 if not less on both.he was running 20/50 wt oil,looks like it shouldve had 20 wt,like our mod motors run. to tight of clearences,to heavy of oil,and excesive rpm ( for comboination and tollerances)what do yall think?
 
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