Here we go. My engine, due to a trashed #4 rod bearing, has recently been stripped. Now lm trying to get it back together. When l put a piston on, lm trying to turn the crank. The first two #7 and #8 went ok, l put them in, turned the crank, the tightened down to the 45 lbs and they turned ok. When l put in #6, it didnt want to turn at all. Finally, w/o the nuts on it, it turned. But w/ any pressure it doesnt want to turn. This is w/ only 3 pistons. l decided l should stop and ask.

lm lubing the bearings (new) w/ motor oil. All bearings, main and rod are new, as are the piston rings. l have kept the caps numbered, as l did the pistons, so this is correct. The crank is one l got from the machine shop. They spec'ed it and its a std size crank. So l got the std size bearings.

What am l doing wrong?

Clayton

 

Sounds like one or more rods are on the pistons backwards...

The rod bearings aren't symmetrical. On the edge of the bearing that is supposed to be next to the other rod on a given journal, they are wider than the edge that's supposed to be next to the crank, and the crank edge is also often suposed to have a chamfer. So if the rod is backwards on the piston, the wide edge of the bearing will be where the narrow edge is supposed to be, which will put it up onto the radius of the crank grind. There won't appear to be a problem until you tighten down the 2nd rod on one journal, at which point the rods will be forced hard against one another.

The rods should be able to freely slide from side to side on the crank, with about .010"-.020" of clearance.

Check to see that the bearing tangs are on the side of the rod away from the cam, that is the "outside" of the whole engine assembly. Also, if you had your crank ground by a racing shop but are using regular bearings, they may be too wide toward the outside edge than the crank will accomodate. You can look at the bearing closely on that edge and you may be able to see the result of the problem. If that's the case, get some Speed Pro bearings or some similar racing ones, not just stock off-the-shelf ones.

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"So many Mustangs, so little time..."
ICON Motorsports

 

i agree with rb. another thing to consider if you had the crank ground is the edges of the bearings binding on the radius from the crank pin to the counter weight.

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ICON Motorsports

1st & 3rd

 

Check to make sure you didn't mix up your rod caps.....I did that one by mistake.

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Riccioli Performance Motorworks

--RPM Racing--

-Currently building first ever engine. 383 with Super Ram plenum and runners, Edelbrock lower intake, Bosch 24# injectors, AFR 190 heads, MSD ignition.
-Will be installing Baer Brakes
-Will be installing full Spohn suspension in rear
-Art Carr 700R4 trans??


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