i also posted this in the General Engine Building forum but it was suggested that i ask here as well so...... i am building a 79 400 to go in my 66 f100. i just got the block back from the machine shop along with the rods and pistons and a new crank kit. the guys at the shop told me that the rods were fine and the block did not need to be line bored or decked but the crank did need to be ground. so i just bit the bullet and bought a crank kit that came with rod and main bearings. my question is about the bearing clearances. i checked the mains and everything seems good, green plastigauge read at .003. then i installed the rod bearings and when i checked the clearances on the #1 piston and rod the plastigauge read .002 on the right side of the bearing and .015 on the left side of the bearing. it also concerns me that there is a small amount of play if i move the rod side to side. this is my first build and i am referencing the book "How to build Ford V8's" by Tom Monroe. i just want to be sure every thing is sound in this motor so i dont end up with a 3000 dollar boat anchor. thanks for any help

 

G'day COLEnMICHAELS66,

Did you mean .0015" clearance or .015" ?. If it is in fact .015" on one side of the rod bearing for clearance then there is a serious issue. Thoughly check it out......it's not right.

.002" (2 thou.) is good clearance but it should be even not tapered like .002 on one side and .0015" on the other, particularly if the crank has been ground as it appears by your description.

A possibility is perhaps the conrod cap faces where they bolt up have been machined off square, this will give weird clearance measurements. Or perhaps something has got caught under the cap when torqueing it up and it is twisting. Another possibilty is the crank jounal has been ground tapered, but highly unlikely.

Side clearance on conrods should be .010" (ten thou.) up to .020". Ford Australia's wear limit on Clevelands is .023" thou. maximum side clearance. Depending on the motors purpose err on the tight side (.010") for a cruiser and loose side for a high winding high horsepower screamer. Measure the clearance between conrod pairs. You will be able to feel .010" movement when you move the pairs back and forth.

Crank grinders that offer packages usually take this kind of info. in and "factor it" depending on what you tell them. So if you tell them that you are building a stock motor the clearnaces will be tighter, street motor a little looser and race motor a bit more clearance.

Ask arround there are plenty of skilled engine rebuilders using this FTE site.

Hope this helps............Barry.

 

I moved my opinion to your other thread.

 

sorry, yes i meant .0015

 

Your 0.003" clearances on the mains are way too high. Check the rod and main clearances again, 0.002" is too high on a fresh rebuild. Clearances that are too high will result in low oil pressure and premature engine problems.

400 bearings should be on the tight side like the Ford service manual recommends. Between 0.0008 and 0.0015".

Normal service limit specifications are:
Rods: 0.0008-0.0026"
Mains: 0.0008-0.0026"
Rod side clearance: 0.010-0.020" service limit 0.023"
Crankshaft end play: 0.004-0.008" service limit 0.012"

There really should be no appreciable taper across the rod or main journals (less than 0.0001" per inch) but the book allows 0.0005" per inch. Taper comes from improperly dressed or worn grinding stones.

Service limits are where you have to do repairs or replace the bad parts.