VT Mechanical Problems - Help

[Dodson]

Hi ,
I am new to these forums however have found many useful things whilst doing the repair on a VT.
A quick introduction, this is the first complex mechanical operation I have done to any vehicle.
About 2 months ago I set out to replace the head gasket which was blown on a VT commodore I had sitting around in my shed. I pulled it all apart and took the heads into a mechanic whom machined them and fixed the valves. I bought a VRS kit and replace all the gaskets whilst doing the rebuild. I put the car back together and sure enough it went. The radiator had a hole in it and the EGR pipe was cracked so I had to replace both of them.

Once I got it going I realised it was idling really rough, enough to shake the car and the rockers were noisy, at least one of them.

I took it down to my local mechanic whom had a look at it and confirmed it wasn’t a vacuum leak which was the suspicion of most, there was a vacuum leak from the heater switch inside (common VT problem I understand) however I have since fixed that. The mechanic did an exhaust analysis and quickly told me there was a lot of unburnt fuel.

I can rule out injectors because the car is duel fuel and runs the same on Gas.
I was advised then to get a compression test done.
I have done a compression test and found that two of the cylinders are low on compression only reading around 90, three of the others were around 130-135 and one was 150.

Since then I have taken the rocker covers off, I originally tightened them to 11-19 pounds as per the specifications in the workshop manual. After playing with the rocker pedestal bolts I found that if I tightened the pedestal bolts I would actually get no compression in the cylinder. However if I leave the rockers really loose I actually get better compression readings, however the rockers would be too loose to run properly like that.

After doing some research that whilst doing the rebuild I may have stuffed up the hydraulic lifter preload? If this is correct what is my best course of action? Do you guys believe I may be on to something or is there something else I should be trying?

Any questions please ask any assistance will be greatly appreciated.

From Dodson

[moose man]

Definitely could be onto something.
If you shave the cylinder head, you lessen the distance between the valve gear and the block (cam), so all other connecting components will not fit the same (lifters, rods, rockers etc will appear to be too long).
However, in saying that, the hydraulic lifters will usually compress a bit (enough for a light head shave) without problems.

When you removed all rocker arms, did compression come back to normal in all cylinders?
If so, your head is too low in relation to the cam (machined too much, or block has also been decked too much, wrong cam, wrong lifters etc.) You can dodgy a repair by spacing under the rocker pedestal with washers.
If not, you have another problem (leaky head gasket, valve not sealing, rings not sealing)

[Dodson]

I didn't try all of the cylinders cause a few of them have good compression, but when I loosened the rocker arms and turned it over on the low compression cylinder the compression was higher, but still not great and it would leak down after compression had gone up, obviously (I'm assuming) because they are lose the push-rods aren't firm against the hydraulic lifters and the lifters raise a little letting the compression seep down.

Apparently if you do a wet compression check and the compression doesn't change it means your rings are okay? So in that case its not the rings. It shouldn't be the valves anyway because the mechanic was supposed to fix them and according to the mechanic whom I went through, he does a lot of work for my father his machinist is normally really good.

Thanks for your response moose man. you reckon i just see how i go if I put a washer there or something before I get it fixed properly?