428 compression

[FL SAAC]

Hi all involved,
Just a few points that may help. According to the shop manual "engine" section a variation of 20 psi from specified pressure is satisfactory. It also says an accurate test is done on a fully warmed up engine, and goes on to say primary  throttle plates open-5 pumping strokes-then record the highest reading. Repeat on all cylinders. Unless you have magical talent this is impossible with an engine installed in a car. The most accurate way to determine an engines condition is a leakdown tester. Knowing most people only dream of owning one they are rarely used. Knowing this engine after years of use it is normal to find worn valve guides which leads to poor valve sealing. The rocker arm geometry on/with oem parts causes the valve to wear out the guide. Worn guides lead to poor valve sealing and  if only 1 cylinder is low on compression it is the most likely cause.

Best advice is open it up while it is out and inspect everything. If you are deep enough to be doing bearings you should not have any trouble finding out why compression is lower in one cylinder. Spend whatever time it takes to clean all parts and be certain to prime the oil system prior to running the engine.

Hope this is useful information. Keep us in the loop as you progress.
Regards R.R.

Big Plus One !

[Jakobs67gt500]

Thanks you very much for all your appreciated advise.

We will pull the tops, since is out anyhow.

I wish you all a great weekend

Best regards
Jakob