Atomic 4 Rebuild (Inprogress)

[Night Watch]

I've tried posting the Q at Moyer Marine Forum, but I don't seem to have the correct privileges over there.

I've started a rebuild (spare engine) using a 1977 "freshwater cooled" engine I purchased last year.
Currently at a work stoppage awaiting parts. The reassembly is going as planned, but I have a question for those that know the answer. The question concerns my initial cylinder head pressures. The engine spec range is 95-110psi, mine are spot on (all 4 cylinders) at 75psi. I'm getting these pressures using the starter to turn over the engine. The engine is freshly rebuilt; cylinder's honed to .010 overbore. The cylinders are lightly lubed and not under full oil pressure yet. I'm guessing I will see higher pressures after the oil pump kicks in at 40psi at "first startup", but this is my first engine to rebuild so I'm not familiar with what to expect.

Condition of parts/block: The engine has new valve guides, valves, valve job by a reputable machine shop in Tacoma, the block was high frequency cleaned, crank and flywheel were balanced, and the block deck was milled, new pistons, rings and bearings, new head and two gaskets. Valves were adjusted and checked twice for proper adjustment. The engine went together with no binding, turns freely. The new head is torqued to OEM spec and the head bolts are holding the torque as I've retorqued and checked several times.

Before I tore the original engine down the cylinder head pressures varied between 70-90psi, the block water jacket passed a 20psi pressure test for 20 minutes, so the block was a "good" candidate for a rebuild.

What am I missing, or am I just paranoid?

 

[kloudie1]

Stuff probably needs to be broken in a bit.. Remove one plug and put in a teaspoon (not more) of engine oil then open the throttle fully and recheck compression in that cylinder.. You'll probably see a significant increase which would indicate that the rings /cylinder interface needs some running.. I am assuming that the rings are installed right-side-up and the ring end gap was checked and corrected if necessary.
Note that if a good bit of the gooey assembly lube was used, the compression oil check won't show an increase and will indicate a different problem that will require some head scratching (Cam timing maybe?) .. I wouldn't think a cracked block or head since that woould most likely affect one or two cylinders and not be uniform as you've indicated.
Good Luck

 

[Night Watch]

Stuff probably needs to be broken in a bit.. Remove one plug and put in a teaspoon (not more) of engine oil then open the throttle fully and recheck compression in that cylinder.. You'll probably see a significant increase which would indicate that the rings /cylinder interface needs some running.. I am assuming that the rings are installed right-side-up and the ring end gap was checked and corrected if necessary.
Note that if a good bit of the gooey assembly lube was used, the compression oil check won't show an increase and will indicate a different problem that will require some head scratching (Cam timing maybe?) .. I wouldn't think a cracked block or head since that woould most likely affect one or two cylinders and not be uniform as you've indicated.
Good Luck

Yes, I did install the rings "right-side" up and used assembly lube to reassemble. So, thanks for your input.

 

[Night Watch]

Will be down in your neck of the woods to see the grandkids next week.

 

[fox9988]

As mentioned, do the compression test at wide open throttle. Please post the results.

 

[Night Watch]

As mentioned, do the compression test at wide open throttle. Please post the results.

You can't see it in the photo, but there's no carburetor or manifold on the block yet. So, can't comply with your request.

 

[fox9988]

Understood. Worst case, run it. It'll go for years.

 

[kloudie1]

That .looks like wide open throttle,