My 400 with tmeyer pistons 0.030 over, crower cam, seems to make blow by under load. at idle and high vacuum conditions no blowby, under load, climbing a pass or steady climb, it seems to make blowby. hasn't used any oil measurable on stickin 2000 mile interval, no smoke, no noise, can't hear any pinging, plugs are gold when I check, won't heat up at all, but there is definrtely some blowby, I can smell it, I can see it in the air filer housing, it deposits oil, lightly, I am going to run for a while longer and then see if a compression test yields anything. Engine sure runs nice, but I hate blowby, anybody else?

 

Blowby would most likely be a ring problem of some kind, not a piston problem.

 

Yes, rings. Not pistons. Maybe they haven't seated yet. Or, too much end gap.

Is the PCV system hooked up correctly?

 

oh yeah, good pcv system, those rings are file fit per the specs, so that was done, and they were gapped slightly less than the recommended by tim but all 8 top rings were filed, the gap they spec is a lot more than I ever ran on a street engine, I just figured more gap=more room for air to get by, means more blowby. I just figured I would ask, if I biuld another one, I might cheat the ring gap less, and see what happens.

 

My local engine builders (there are 3 that I deal with) all said that a wider ring gap is almost always prone to leak compression, but not severe enough to worry.

 

Agree. At low RPM, or when doing a compression test, you might get a bit of leakage. But at any reasonable speed the leakage will be minimal.

 

I like cast iron rings,and these thin rings are moly, or chrome or "hard" I have had 2 or 3 engines with these rings, and thes seemed to have blowby, and the rest of my engines had normal or conventional or cast iron. The other engines of mine don't have blow by. Maybe the ring type is less affective than the hone/bore condition, but in my engine building, which ranges from small single cylinder 4 cycle and 2 cycle to I-4 to v-4 to v-6 to I-4 N/A diesel to I-4 turbo diesel, to I-6 NA diesel, to I-6 turbo diesel, to v-8 gas, to v-8 stroker gas, to v-8 NA diesel to v8 turbo diesel, and probably some in between, Pretty much thewider the ring gap, the more blow by, the closer tolerence the better the blowby. Any engine. Just asking if the condition I am seeing is common. The one engine builder claims to not build anymore engines with pistons requiring "wider" ring gap, on account of worse temperements like I have. Blowby.

 

in a sense it could be the pistons, cause hyper pistons require a larger ring end gap. But I wouldn't think enough to notice.

 

Add compression add blowby. There is a sweet spot though. What end gap factor are you running on the rings? Before I dropped a valve on mine I was running a .0075 end gap factor (nitrous build) and I never had a big blowby issue. Angled the ring gaps away from each other right? If they spun upon installation it might pass a little but still shouldn't be much. If all else fails stick an oil/air separator into your PCV system and it'll quit getting up into air cleaner. Or a crank case evac setup run to headers (or exhaust) will keep vapors down

 

How much preload do you have in the lifters ?

 

Lifter preload might be worth verifying, I feel there is very minimal. Upon assembly with collapsed lifters, the pushrod wouldgointo the lifter a good 0.060" more, on a cold engine. This was about as much additional clearance as I have ever ran, but upon warming up, the clearance is going to become less. Lifter preload might be a concern. I was considering pulling valve covers, I have a few worn rockers that are ticking, replacing all of those and possibly ordering shorter pushrods, see or putting a shim under the rockers; the shim would shorten pushrod length as well as help valve train geometry.

I am confident in my ability to properly install and file fit a ring, I have done it lotsof times. As far as blowby increase as compression increases, That doesn't necessarily prove out. I have biult plentyof 10:1 and north of that engines, 460s, 390s, 429s, and I have found that if everything is right, blowby is OK, if lots of blowby, there is probably something wrong. Mine doesn't havea lot of blowby, not enough tobe concern, but more than none.

 

I installed the ring gap per the KB documents, those are 0.0065 for street and 0.0080 for towing. I do tow, but not significant. This was putting a ring gap for a 4" bore 0.026" My rings were all consistent at 0.015" out of the box, I mixed and matched, pretty consistent. Then I filed them open, to attain a gap of 0.023"-0.025" respectively. I felth that these rings would wear in, putting the gap wider.

 

Hmm .026 top and second? You're right per street spec there shouldn't be blowby. 4.0" bore at how many miles before pistons?

 

.060 is on the edge of too much. It could cause a compression leak. I never run more than .030 with the cam on the base circle, piston at tdc. Tighten the rocker till it just touches the push rod. Set up a dial indicator on the rocker zero the indicator and tighten it, see what you got. Another thing were all the valve tip heights equalized when the valve job was done ? If not you got a mess on your hands, you will have to go through this with every cylinder. Imo piston rings you put in, unless you put one on upside down or gaps lined up (not likely) I doubt that's what causing it. Did you do a leak down on it ?

 

I really haven't done any diagnostic, as I am not too concerned, I hauled a load over 2 mountain passes yesterday and back, I will say that under load, higher rpm, it makes blowby, deposited about 2-3 tablespoons of oil in the aircleaner, then under normal conditions, all is well, cold, hot, fast, slow, the pcv corrects anything. leavesit unnotices. Just towing uphill for long duration, it starts to make blowby and deposit oil in the aircleaner. This is not the first time I have seen this. I have had a couple 460s do this as well. I think that there might be some compression leaks in the valve train under high rpm, Reason I feel this way is because the oil system mods make pretty high oil pressure, and that will "inflate" the lifter under higher rpm, like towing a mountain pass. This used to happen often on the 460s that were used to tow years ago. The valve job looked fine to me, I sure didn't notice anything out of place or erratic. Thanks for the input.