Anyone running a P90A head? Need Help!

[hls30.com]

I think you have too much pressure building at the lifters-a blockage in the drain so to speak.

Maybe the extrernal cam oiling pasages were the bleeds for the lifters, and now that they are blocked off, they are allowing pressure to build in the lifters, locking them open.

I would get Vernon involved-it sounds like something that was blocked off needs to be opened back up-even if only partially. He knows what he did-he was there when he did it! Explain the problem to him, and let him give you a testing procedure-but dollars against donuts the problem is in the conversion...

Will

Will

[mlc240z]

if pressure is locking the lifters, how about popping the valve cover off while the engine is running? don't know what kind of oil splash you would get with an internally oiled cam but some sort of shield could be fabricated.

just try to confirm what's actually happening.

you might be able to see the lack of lift or excess of lift of the valves as the engine started to die.

bart

[ZSaint]

I got some info sent to me by a car-building buddy. It came from The Datsun Workshop. Three things that cause "Bleed Down" are 1) Low oil pressure/volumn. I have installed a new turbo pump with 75#2) Bad lifters All of my lifter are either bad or there is another problem AND 3) One of the problems with running these Datsun lifters is "too much valve spring pressure". This causes the lifters to "bleed down". I have sent Vernon an email to get his opinion on the head. I also asked him about the springs he installed. This 'Workshop' info states that 100-110# closed and 230-250# open is the max you can run. (before you experience bleed down). Stock ZXT springs run 70-80 and 160-170. I am wondering if they intalled some of these 270-300# valve springs? I think that is what comes standard with most high-lift cams.

I am guessing that either there is blockage on the oil system that keep oil from flowing out of the lifters or it is too much spring pressure. Because it starts right up and runs well for a short period of time leads me to the conclusion that my springs have too much pressure. What do you guys think?

[hls30.com]

I don't think you are having a low oil pressure situation(well, maybe relative to spring pressure) but other =wise I think you are all over the problem-let us know what Vernon says!

Will

[mlc240z]

high spring pressure sounds like a reasonable theory to me.

bart

[LanceM]

It is my thinking that bleed down would cause excessive clearance, by being bled down the lifter would not be lifting to all the way, lack of bleed down would cause the lifter clearance to go to zero and cause excessive lift/minumum clearance.

All of my experiance is with SBC, but in any case a hydralic lifter works the same, zero lash. I agree with one of the earlier posts that you must have some type of return blockage, where the lifters pump up and the oil can't escape, pumping them up to the top with enough pressure to overcome the closed spring pressure holding the valves open. I don't know squat about Datsun lifters so they may be a whole nother ball of wax but I would think that in theory they would all work the same... In any case I've never seen a lifter fail because it pumped up and wouldn't release, they always fail because they won't pump up, wether it's because of a collapsed spring inside or excessive clearances in the lifter itself (worn out)... I would think that excessive valve spring pressure would overcome the lifter giving you a won't pump up effect as the spring pressure is greater than the hydralic pressure in the lifter forcing the oil out of the lifter and reducing your lift.

Anyway my $.02, looking forward to what the builder has to say...

[sideshowbob]

It's a wild guess, but... The conversion to an internally oiled cam may have caused an increase in pressure if the oiling holes are considerably smaller to the cam. While this doesn't affect the mechanical setup, it could conceivably cause this problem. More so if the conversion was done incorrectly (if that's the case, you'll quickly lose your cam, hydraulic or not). I don't have the engine oiling diagram in front of me and can't verify the direction of flow. Anyone know more?

[sideshowbob]

Oh, Lance: You're correct there. In other motors I understand that a competition cam REQUIRES heavier springs to drain the lifter. Perhaps your valve springs have had it?

[LanceM]

Oh, Lance: You're correct there. In other motors I understand that a competition cam REQUIRES heavier springs to drain the lifter. Perhaps your valve springs have had it?

They require heavier springs to prevent valve float at high rpm, they have nothing to do with draining the lifter, that happens when the oil hole in the lifter drops below the lifter hole in the block and opens itself to the return oil galley in a SBC.

An to your other post, a P90/P90A head uses an internally oiled cam, so the cam lift is the only real modification to the head in this case.

[sideshowbob]

I stand corrected.

[LanceM]

No big deal, life is a learning process, learning usually ends at death... except for those that already know it all, their death came sooner just they haven't stopped breathing yet...

[ZSaint]

Who do I contact other than Vernon at Raver. He is not responding. Will Ron at Nissan know about these hydraulic lifters?