1993 Mercruiser 5.0 V8 short block assembly

dlogvine

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Im trying to reassemble 1993 V8 5.0 Mercruiser engine. It was rebuild completely, so we started with the camshaft and crankshaft. Then we inserted new pistons with the rings. Both rod and crankshaft bearings were replaced with the new ones. The problem started when I tried to torque the rod caps. Even when they were torqued to less than 20 feet pounds the engine started cranking with difficulty, when I tightened the nuts a little more to 20 feet pounds, the cranking became really difficult. I lubed the cylinders and pistons with new oil, bearings and the crankshaft with the assembly lube while assembling them. I double checked the rod bearings and caps for correct orientation, all were installed properly. Now the question is, what could be the cause of hard crank? Should I maybe use more lube on the rod bearings? or could there be any other problem?
 

Bt Doctur

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did you measure the crank journals for O.D and the connecting rods I.D. What were the measurements?
 

ihc1470

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Quick way to do what Bt Doctur is telling you to do is with plasti-gauge if you do not have the mics to do the measuring with. You can get that at most any good auto parts store. Napa, Auto Zone etc. You put a strip of that on the crank, install the bearing and torque to specs then remove and see how much crush there was. Try not to turn the crank while your doing that as it will mess up your readings.

Did you have the crank turned by chance? If not did they sell you undersized bearings for the crank or a bigger undersized bearing then what the crank is turned too by chance? Both the mains and rods should be marked on the back side of the shells.

Good luck in discovering what your problem is.
 

dlogvine

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I did not measure the crank journals and bearings, the crankshaft was resurfaced in the shop and the bearings were brand new, came in the kit. I assumed the shop would give me the right size bearings. I'll get the plastigauge tomorrow to measure the crush. Do I have to do it in all the caps though or any ones in particular?
 

ihc1470

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Your saying crankshaft was resurfaced which I assume means ground undersize. Did they do all the journals or just mains or rods. One would assume that the bearings would be correct and they should, however in this case I am guessing there is an issue since your not able to turn it over correctly. I would do them all just for the peace of mind of knowing what you have.
 
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JustJason

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I assumed the shop would give me the right size bearings.

It's up to the mechanic assembling the engine to measure everything in the block out. The minute you assume just 1 thing is the minute the engine doesn't go together the correct way.
 

Scott Danforth

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JustJason nailed it

you as the assembling mechanic need to measure the block journals, the rod journals, and the crank journals with a micrometer to make sure the machine shop did not miss a step. you also need to measure the bearings, then use plastigage to verify tolerance. you also need to check end play on the thrust bearing with a dial indicator

Never assume.......and measure everything.....

if the machine shop made an error, they will most likely correct it. however if you damaged the bearings by installing without measureing, you will need to replace them.
 

wrench 3

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It may be a dumb question, but is there any chance that the rod caps got mixed up.
 

Bt Doctur

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the rod caps shouldnt really make a difference .When you re-condition a rod you assemble the cap and torque it in place without the bearing , then recondition it. My guess the shop sent the wrong size bearings. It happens. Conditioning a crank makes it smaller , not bigger. If the shop cut it 10/10 it means the mains and rod bearings would be be stamped +10 .If they only polished it . a oversized bearing would not work.
 

wrench 3

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the rod caps shouldnt really make a difference .When you re-condition a rod you assemble the cap and torque it in place without the bearing , then recondition it. My guess the shop sent the wrong size bearings. It happens. Conditioning a crank makes it smaller , not bigger. If the shop cut it 10/10 it means the mains and rod bearings would be be stamped +10 .If they only polished it . a oversized bearing would not work.

But if the installer put the cap onto a different rod, you would not necessarily have a round hole. Just one of the possible causes.
 

dlogvine

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we had the caps numbered and numbers were stamped when we took it apart. The camshaft is new, came with the kit, together with the rod bearings. Will check the clearance with the plastigage tomorrow. The only thing I can think could be wrong are the wrong size cap bearings. Crankshaft and camshaft were moving easily when torqued.
 

Bt Doctur

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The camshaft is new, came with the kit, together with the rod bearings.

The machinist ordered this kit? you would need to know the crankshaft/rod dia. first. what markings do the bearing have stamped into them and was the crankshaft cut or just polished.
 

dlogvine

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Crankshaft was polished, did not need any resurfacing, was in a good shape. And i found the problem, makes me feel so dumb, we looked at the pistons at least 10 times and only when i was measuring the rod gaps with the plastigauge, i found that piston 5 was installed backwards. I feel like an idiot, also i checked all the gaps and they were all up to spec. Thank you all guys, i really appreciate all the help.
 

dlogvine

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The camshaft is new, came with the kit, together with the rod bearings.

The machinist ordered this kit? you would need to know the crankshaft/rod dia. first. what markings do the bearing have stamped into them and was the crankshaft cut or just polished.
The rods and caps had matching marks, we stamped them by the cylinder numbers, from 1 to 8
 
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