crank oil clearence-68 350ci

[herk402]

Oil clearance on my 350 are working out to be .003. The engine will have an 068 cam,
TRW forged pistons .030, 650 4bbl, 2.5 dual exhaust. Mild porting, stock rockers,HEI ignition,T300 2speed AT & stock rear. All in a 68 Lemans conv. First off how does this combination look for HP gained for $ invested. And second I've had conflicting feedback on the oil clearence being to large. Any thoughts/input would be great. Please be gentle I'm new at this & also having a midlife crisis. So my wife says--Hell I'm only 40--Thanks

[herk402]

Oil clearance on my 350 are working out to be .003. The engine will have an 068 cam,
TRW forged pistons .030, 650 4bbl, 2.5 dual exhaust. Mild porting, stock rockers,HEI ignition,T300 2speed AT & stock rear. All in a 68 Lemans conv. First off how does this combination look for HP gained for $ invested. And second I've had conflicting feedback on the oil clearence being to large. Any thoughts/input would be great. Please be gentle I'm new at this & also having a midlife crisis. So my wife says--Hell I'm only 40--Thanks

[Phil69GTO]

What rear-end ratio are you running?? I think you combo sounds like a good ride and the 068 is a great cam, but remember we are talking a 350 ci engine here. You might even be happier with a little less cam, depending on what your rear-end ratio is. I'm not too versed in 350 Poncho mods, so maybe others can help. I like the 068, just like it better in a 400. As for oil clearances, I like to shoot for .002-.0025 on both rods and mains. .003 will cause some small loss in oil pressure but I'd rather be on the wide end of clearance versus the tight end. Anyone else wanna take a shot at this ??!!

[PONTIAC DUDE]

.003 all the way thru is tooooo much. On the mains I could live with that. Also is that with a mic or That fit-all plasticgauge? Street at .002 on the rods & run your side clearance between the rods at .012. need to get the oil out of the block to keep things cool & keep from burning up a bearing, but not to loose on the street to create low idle pressure. Run synthetic oil as low pressure works better with this type of oil and takes more load. If this a stock crusier that's not going to be hammered then all you need is .015 on the rods & .015/.002 on the mains with .008/.010 side clearence. as the horsepower increases your clearances NEED to increase in proportion. Occasional running: .002 on the rods/.002/.0025 mains with .010/.012 side. Higher rpm open up the side to .015 Later.

[This message has been edited by PONTIAC DUDE (edited 03-15-2000).]

[TinInjun]

Pontiac Dude hit the nail right on the head herk. One thing you you didn't mention was the crearance you will be using on the .030 over pistons. Remember they are forged and expand more and at a different rate than cast. I would not run them any tighter than .0055. They might make some noise (piston slap) when the engine is cold, but the engine will quiet down once warmed up. If you are not going to rev this motor higher than 5500, I would just stay with cast pistons and save some money. Just my 2 cents
George

[herk402]

Thanks for the responce guys. I'll try to give you the info you asked about. I think the rear is 2.73 I'm thinking of going to a 3.23 I heard that was still ok on the highway. The pistons clear at .0058, so sayeth the machinist. The crank was first measured via the plastigage then miked out. Both read .003- 2 local sources said that .003 would be just fine with a high volume oil pump& synth oil. What kind of HP would ya think this will make? Thanks again for any & all past or future input. This board is most informative. thanks

[77TA]

I just went throught this and this is what I have found. anything from .002 up to a max of .004 will most likely be ok. See Clevit Bearing web site they reccamend .001 per inch of bearing journal +.0005. They should know something about bearing clearances. Jim Butler does not reccamend going less than .0025. Nunzi told me I was ok at .003 so I left mine at that. My machinest is in favor of .003 to .004 on the mains with large journal cranks like the 455 in High performance usage. I think th range is wider than most beleave it is. I will let Ya'll know what my oil pressure looks like after the thing is togeather though it might be a few weeks.