rebuilt motor that is too tight.

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pett3227b
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rebuilt motor that is too tight.

Postby pett3227b » Tue Jun 20, 2023 3:48 pm

I have rebuilt my 47' motor and assembled it and it was too tight to turn over the crank with the hand crank. I have made a few posts about it. I did neglect to lube some of the friction wear areas. I plastigauged the main and rod bearings. They are within spec. I had a machinist check the piston to bore clearance and It is a little below spec. The manual says that it needs to be within 1.6 to 2.4 thousands in clearance. The actual clearance is 1.5 thousandths. My question is should I have my machinist hone the block a little more and get it within the proper range? It's mighty close but would it help much?

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Re: rebuilt motor that is too tight.

Postby Eugene » Tue Jun 20, 2023 4:29 pm

pett3227b wrote:I have rebuilt my 47' motor and assembled it and it was too tight to turn over the crank with the hand crank.
I had a machinist check the piston to bore clearance and it is a little below spec.
Your machinist recommended what?

Recommend you disassemble the engine one piece at a time. After piece is removed, check to see if you can turn the engine with the hand crank.

My guess, rod and/or main bearings are to tight. Another option, wrong piston rings.
I have an excuse. CRS.

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ricky racer
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Re: rebuilt motor that is too tight.

Postby ricky racer » Tue Jun 20, 2023 4:49 pm

Was the ring end gap within spec? Normally main or rod bearings too tight would be the suspected problem however you said the clearance was good. The next thing I'd suspect would be the piston fit. I doubt the. 0001" undersize would cause the issue but no end gap could.
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tst
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Re: rebuilt motor that is too tight.

Postby tst » Tue Jun 20, 2023 6:54 pm

did you end gap the rings ? did the crank turn easy before loading the pistons in the block ?
I have rebuilt many of these for customers, with the rings end gapped and on the piston, install in cylinder and see how it slides in cylinder with out being bolted to the crank, I did have a set of new pistons once where the ring grooves were not machined deep enough so they were super tight


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