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Old 04-13-2009, 12:44 PM
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Last question before SBC off to machine shop (oil consumption)

As many of you I have been struggling with oil consumption with a 383 stoker SBC for a year. The engine has 800 miles and the rings are plasma-moly. A brief recap is I did a compression check (good...190 in each cyl, +15psi wet), pulled intake and checked if pulling oil from intake galley (no oil), checked back of intake valves (clean); investigated PCV system (fixed to match OEM, was missing breather and baffles) inside intake under carb seems clean...also rear main started to leak recently making it harder to follow oil consumption. The latest is 1.5 qts in approx 100 miles. I get greyish color smoke at idle but when I really see it is at WOT and deaccelleration with black oily residue in the tailpipe. (less smoke when I run it 1-2 qts low....7qt pan) Talked to 3 machine shops all said tear down was in order that something was up with the cylinders/rings. Tear down and put back together with new hone, rings and gaskets (some performance) is going to run me some $$$ already have good amount of $ just in machine costs and parts (not including original labor). I pulled the engine this weekend and found a few ounces of oil in the bottom of the bellhousing (see pic); pretty much pointing to the rear main seal leaking. However after checking the exhaust ports and hedders they are filled with a black carbon like residue but does not feel as oily as what is in the tailpipe and what I EXPECTED , more dry. I plan on pulling both valve covers and backing off the rockers to make sure the valves are closed and doing a leak down test before I send off to machine shop. I am worried that the machine shop is not going to solve my problem and I spent all this time and $ for nothing

Any last thoughts before tomorrow turning back after I drop it off.

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Old 04-13-2009, 01:06 PM
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Originally Posted by y2k600f4
Any last thoughts before tomorrow AM
I just can't see that kind of oil consumption coming from anywhere but the rings.

The valve guides would have to be horrible for the losses to be from them- I just don't see that happening.

I would say go ahead and bite the bullet and have the cylinders re honed and fresh rings installed.
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Old 04-13-2009, 04:16 PM
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Aluminum heads, that means pressed in guides, these need care upon installation and a final hone or ream after installation. This is where things can go wrong. Also the seats must be done after the final hone/ream, otherwise the valve seat--thus the valve head isn't square to the guide. Wear really goes up when this happens.

Also press in guides and the valves stems contained there in run hotter than say a cast iron head with an integral guide, this also can contribute to excess wear. One needs to be aware of engine operating temp and cooling system pressure. Trying to overcome aluminum's fast heat transfer rate by running the engine op temp up can get these things too hot, especially at a local level where metal temps can run 3-400 degrees hotter than the surrounding coolant resulting in poor specific surface cooling because of local boiling but you're not aware of that because the average coolant temp going back to the radiator return looks normal. This goes back and forth with guide lubrication, positive seals starve the guide, one needs to be considerate of the materials used. Bronze alloy guides can run dryer than cast iron with a tighter clearance. However, valves with chromed stems need more oil and at the same time they give up less heat which causes them to expand more so you want to start at the looser end of the acceptable clearance. The reason for oil starvation is that shinny surfaces are harder to wet, so wear with them will go up from that stand point as well as they will expand more and eat up the clearance if there isn't enough of it. Have them carefully looked at by a knowledgeable person. They're looking for discoloration, gouging; things that show abnormal temperature and or wear in both the stems and the guides.

None of this is to eliminate ring, piston, or bore problems, it's just there's a lot of details to look at and have an understanding of. And these places are no less exempted from details such as making sure the bore hone roughness is compatible with the ring type being used. End clearance of the rings, as well as clearance and cleanliness of the lands. This can especially be a problem where gap-less rings are used as the rings have to twist and seal at the ends of every stroke. If they can't then blow by gets out in one direction and oil gets pumped into the chambers in the other direction. This is also true of up to down alignment, a ring put in upside down, well works upside down in that if it were a oil scraping ring like number two, it's now pumping oil up into the top ring and combustion chamber instead of down to the oil control rings and back to the sump.

While we're at the sump, you said you've got a seven quart pan. Do you know where the oil level is in the sump. It needs not to be any higher, if as high, as the stock level. Too high will create a situation where the oil can't settle back to the pan and being whipped up by the crank puts more oil on the underside of the piston than the rings can squeegee off the bores, or the level is high enough to where the crank is clipping the oil off the top of the sump with similar result to the preceding description. The oil pump and bearing clearances need to be considered, a high volume pump and loose clearances puts a lot of oil in circulation as it comes off the journals. This results in flooding out the oil control rings if careful attention isn't paid to oil scrapers, and windage trays. something has to be said about the pump and or pick up as well; with a deep sump pan, assuming its getting to 7 quarts with more depth, the pump or the pickup needs to be lowered such that the pickup's entry is about 1/4 to 3/8 inch above the bottom of the pan. If it isn't, a vorticity will form drawing air into the oil entering the pump. This will carve up the bearings in short order letting a lot of oil to fly around the crankcase. In the case of a high volume pump, you might not see this as a loss in oil pressure for awhile but the rings are none-the-less drowning.

One also needs to consider rod straightness, a bent rod twists the piston into angles where the rings become dysfunctional. Look for wear on the piston, up and down is a straight rod, any angularity isn't. Don't forget skirt clearance, excessive clearance like a bent rod allows the ring pack to twist from normal to the bore, this lets blowby and oil around the piston. Don't forget to chenck the size of the piston against the overbore, I swear to you, I taken more than one engine apart to find the piston overbore to be less than the cylinder bore's with the correct size ring package in the piston. Burnt oil like you wouldn't believe, but they also ticked as the skirt reversed thrust direction going thru TDc and BDC.

So I guess where I'm going is that there are a lot of potential problems than won't show on either a compression or leak down test, not that you shouldn't do those tests, but if they don't point at something, don't assume all is well.

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Old 04-14-2009, 05:39 AM
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I,m with bogie on the oil level if lowering it slowed the oil loss something is up with either windage or oil level plain to high.To burn 1.5 qts in 100 miles you would be killing every mosquito within miles.While it's out double check for leaks all around the engine.Good luck.
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Old 04-14-2009, 07:12 AM
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You should have done a leak down test as that is more accurate then a compression test, Last we a guy called that owns a Covette and said his oil was getting very dirty in 100 miles and he did a compression test and they were between 170 and 200.

I did a leak down test and this engine that ony only had 400 miles on it since it was toataly rebuilt and the best cylinder was 10% and the worst was about 35% anf the average was 18 to 22 % leak down. And a new engines that built right should have less the 5% leak down.

I should have it here in the shop to find the problem with ring seal and I suspect it was not plate honed as i have seen this to many times.
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Old 04-14-2009, 12:05 PM
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Thanks everyone with your tips, opinions and knowledge !!! Great help and I learned and am learning a lot of the complicatins of building a High performance engine.

This is the current update from the machine shop:

1. Puddles of Oil on top of cylinders, cylinder walls glazed
2. Oily in intake…due to pcv sucking up bowby (visually looks clean)
3. Stretched timing chain… truck double roller was used
4. Main bearings hitting crank, loading rods, need H bearings (clearances not previously checked)
a. Called eagle (manufacturer of bottom end)….aware of potential problem
b. Installer’s responsibility to check clearances
c. Needs replaced, won’t warranty w/o replacement
d. Problem waiting to happen
5. Not good hone…barely see cross hatch…cause of rings not seating
6. Wrong intake gasket should be Felpr 1206 not 1205 (matched up)
7. Too much cam….running rich causing gas in cylinders to wash out rings cause of rings not seating (not matched to rear 3.08)
8. Rear main was not leaking…rear of oil pan: rolled lip of gasket

Looks like its going to cost me some $$

Last edited by y2k600f4; 04-14-2009 at 05:24 PM.
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