Blowing Smoke At High Rpm

[Brodie900]

Hi guys, just thought I'd share this as I'm a little confused about whats going on here.

 

I recently blew a head gasket in my 81 280ZX, evident by water in the oil and compression leaking into the cooling system. 

 

So, I pulled the head off and had it sent to a specialist to get resurfaced and crack tested. I came back all good with a full gasket kit ready to install.

 

The bores looked ok, no scoring or cracks that I could see.

 

I reinstalled the head with ARP studs and torqued everything in sequence as per the FSM.

 

I drove the car about 500k's before really giving it full throttle and winding it out but that was when I noticed the cloud of blue smoke in my mirror! it seems anything under around 5000 rpm is totally fine but over that and a noticeable amount of smoke is coming out and its killed my top end performance completely. The motor used to rev out quite happily before I took the head off but now it only pulls hard up to 5k then just gives up. Also this is the first time I've noticed any smoke at all

 

my first thought was the rings have given up so I checked compression, I found 160psi across all cylinders with a cold engine then i realised I needed to test it hot so I drove it down the road and back then repeated the test. This time I got around 185psi on all cylinders. both of those numbers seem to be within spec for a good engine right?

 

So now i'm thinking its valve stem seals, I'm not sure if they were replaced when the head was done or not but I assumed they had been done. the fact that there was a full set still in the gasket kit that came back with the head suggests the old ones might still be in there tho.

 

what do you guys think? is it possible I haven't run the reco head in properly and ruined the valve seals? or are my oil rings giving in while the compression rings are still holding?

 

 

[dat2kman]

Cylinder pressures are all good.

At higher rpms the valve train gets a lot of oil pumped up around it.

If the stem seals are a bit on the old side, then yes they can let a bit of oil through, but usually when you lift off the accelerator.

Shop should have fitted the new ones.

 

Also, and this wont solve the blue smoke, did you re-torque head?

[Brodie900]

Yes, the head has been re-torqued.

 

I'm thinking I'll just do the valve seals using the nylon rope method and see what happens next