Anyone running a P90A head? Need Help!

[ZSaint]

I am having problems with my camshaft and lifters. It is a solid cam with hydraulic lifters. (They do not grind a cam for hydraulic lifters, so I am told) I know you cannot run this combo in other engines. Raver Motorsports built this head with this camshaft. Here is the problem:

You can start the car and it will run OK. After it runs for about 5 minutes the lifters guit working. I believe they over pump and the engine has no compression. It will not restart until the lifters leak back down. When you check the compression, there is none! After it sets overnight, you have compression and it will start.

Anyone else running the P90A head? What camshaft are you using? Anyone have any ideas on how to fix this head w/o changing to solid lifters?

[First Gen Z]

I haven't experienced this problem so this is just a suggestion. Try increasing the valve clearances by .002 and see what happens. Maybe even a bit more. Experiment a bit. Since you are loosing things there is no chance of hurting anything.

[ZSaint]

I am not aware of anyway to increase or decrease the valve adjustment with hydraulic valves. Do they need to be adjusted? How do you do that? Is there anyone out there that has played with these Datsun hydraulic valves?

[Corganx33]

Everything I've read says that if you use the p90a head with hydraulic lifters you've got to use the stock cam with it because the lifters aren't able to "lift" any further to accomodate a higher lift cam. This is one of the reasons ppl choose to use the P90 instead of the p90a, to avoid the hydraulic lifters.

Not speaking from experience, just from what I've read as I've gone along and tried to decide what head to use in my car.

[ZSaint]

I agree. I have ordered a set of .150 lash pads, mouse springs and adjusters to convert this head to a P90. I do not think this will be too difficult a task. I was kinda looking forward to not having to adjust valves, but I guess that is all part of running a Z. Raver Motorsports put this head together. It simply does not work. I guess I will be selling these lifters on eBay, soon!

[mlc240z]

is it possible you haven't done the "initial" valve adjustment yet?

i had to 'adjust' the hydraulic valves on a '72 camaro i owned when i had a lot of miles on it and noticed a lack of oomph.

basically the procedure was set it at tdc and then check only certain (intake/exhaust) valves. then rotate the cam to the next position the manual called for and adjust the other valves. adjustment involved spinning the valve stem with your fingers and tightening the rocker post nut until it just stopped.

sorry for the vague description but it was over 20 years ago and i just followed the procedure in the manual.

might not be the same exact procedure with your Z, but there's got to be some kind of initial adjustment when you put the head on the car.

[hls30.com]

Before you open everything up and get all dirty-have you verified your oil pump, and used a good mechanical OP gage?

Also what have you got sending extra oil to the turbo(maybe a check valve is in the wrong location.)

Something is filling up and holding pressure from your comments-an oil accumulator perhapse...seems to me the problem is in the plumbing-not the valves.

Will

[sblake01]

But then, how do you explain the loss of compression?

[ZSaint]

Blakeney has it right. Lack of compression means the lifters are pumping up and not releasing. I have installed a used turbo pump and then a new turbo pump. They both have the same result. I do not have any "adjustment" on the Datsun lifters. I know you have to adjust the lifters on a Chrysler but this Datsun does not have any adjustment.

I think what is happening is this... The solid cam has .008-.010 valve clearance. The lifter tries to expand for 'zero' clearance. It continues to pump up until the valve will not close. I am putting the solid adjusters in place and setting the valves. I think this will solve the problem.

[sblake01]

That make sense to me. IIRC, back when I worked with V8s, they had optional hydraulic lifters specifically for higher lift cams. You couldn't use the stock ones beyond a certain lift and I seem to remember experiencing the same problem with a small block ford I once owned. Since, AFAIK, there are no other hydraulic lifters available for the P90A other than the stock ones, solids are you only option.

[hls30.com]

If oil pressure holds the lifters open, how could the engine have compression?

The answer is it could not-an open valve cannot contain!

There is only a fluid force against a spring to make the valves follow-either the springs have a problem, or the fluid pressure is not being released-whether through mechanical interference within the valvetrain, or a simple hydraulic restriction(have you looked at how engine temperature fits in? Maybe some tolerance is off, and heat is closing an oil passage out of the valvetrain).

Replacing the valves with the conventional setup will quickly get the car running, but it does not address what is causing the problem. It is like replacing the L series engine to fix a leaking head gasket! The lifters do not pump! They react to the oil pump! In switching the oil pump(assumimg both that you used are good) you should move on down the oil path-something has to be causing a restriction-and when you get on the correct side of it you will find high oil pressure. Did you replace the oil lines to the turbo-did you put a restrictor in the turbo oil line? (I have seen that there is a need for a restriction in flow through the bearings.)

If you are that sure the hydraulics are the problem-don't sell them to someone else with out disclosing that you believe they are causing this issue.

Get Raver involved-if they built it, they should stand behind it.

Will

[ZSaint]

The head has been converted to an internally oiled cam. The exterior cam oiling passages have been blocked off. This is a stock-appearing engine with dual SU's. The short block was put together by Hatch Engine Service. The head was put together by Vernon at RaVer Motorsports. This camshaft has .450 lift. WEB Cams said they did not think it would work before I had the egine running. I have built a couple of Chrysler engines, a 340 HyPro and a 360. Both of these engines have special hydraulic lifters for the high lift camshafts. They are adjusted as needed. You crank the adjuster down until the engine misses and back off 90`. There is no such adjustment on the Datsun lifters.

Are you saying that I am not getting enough oil flow to the lifters? Where would look for a blockage? Oil is flowing into the head, the cam is oiling and the lifters are getting oil. I think it is working properly. I feel the solid cam will not work with hydraulic lifters. They do not work in any other engine so why will it work in the L6? WEB Cams said exactly that when I talked to them.