Engine Tight After Installing Piston

T

TimTheEmchanter

Junior Member
Hi All,

I’ve been working on a rebuild of an engine and went through and check the main bearing clearances and everything was generally okay, inspec. I started check rod bearing clearances and they actually seemed better than the mains, and I started installing them #4 -> #1. I would check rotation on the crank with pistons in, there was a good amount of resistance, maybe 35-40ftlbs. I install the first piston and the motor completely locks up. Shim it twice with .003 on both sides and still locked up. Not sure what to do at this point? Keep shimming or maybe shim the front main? The piston moves up and down in the cylinder just fine when I disconnect from the crank so I’m confused at this point and need help lol
 
Is there any chance you've reversed a cap, or over-torqued a rod bolt?
I'm guessing you're rebuilding with the original crank/rods?
Just rings, or new pistons/rings?
With the head off, or the plugs out, there should only be a little resistance.
Was it okay before you started attaching the connecting rods?
If so, i probably wouldn't mess with the main shims.
 
Martinbuilt said:
Is there any chance you've reversed a cap, or over-torqued a rod bolt?
I'm guessing you're rebuilding with the original crank/rods?
Just rings, or new pistons/rings?
With the head off, or the plugs out, there should only be a little resistance.
Was it okay before you started attaching the connecting rods?
If so, i probably wouldn't mess with the main shims.
Click to expand...
I can check for those and try again. Rebuilding with original parts, got new rings though original pistons. Rotation was fine with just the mains on, not much resistance, once I started adding rods it got more difficult but still doable. The piston #1 made it lock up hard, more effort to turn than I was comfortable with on the engine stand. Would shimming each rod potentially loosen it up?
 
If it rotated well before you took everything apart, nothing should need shimming. Maybe there was a shim on #1 that was lost? I can't think of much else that would lock up your crank.
Someone else might jump in with another suggestion.
 
Martinbuilt said:
If it rotated well before you took everything apart, nothing should need shimming. Maybe there was a shim on #1 that was lost? I can't think of much else that would lock up your crank.
Someone else might jump in with another suggestion.
Click to expand...
It was locked up before, typical barn find. Felt that I was on the right path since everything was rotating before the #1 piston went in. I’ve shimmed #1 twice and still locked
 
The things that can cause the lock up are: Tight rod bearing, tight piston, tight rings, or bent rod. Here is what to do:


  • Loosen the bolts on the rod to see if that helps. If it does then take out the rod and piston and bolt up the rod without the piston. If the rod then turns OK that would indicate that the rod is bent. Have all the rods checked for bend, twist, and parallel ends.
  • Take the rings off the piston and put the piston in the bore to see if it is tight in the bore. If so then measure the bore and piston to see what the problem is.
  • If the piston is OK then put the rings in the bore (one ring at a time) and press it down into the bore about 2 inches with the piston. That will align the ring with the bore. Measure the gap. The gap should be according to the instructions that came with the rings but about 0.012. Do this on all rings.
  • If the rings are OK and the piston is OK then put the rings back on the piston and put it in the bore without the rod attached. If it is tight in the bore then check the ring grooves for the proper depth. You can turn the rings around to check the depth or just push on the rings to see if they are then flush or below the diameter of the piston. Clean out any carbon in the grooves with an old broken ring. The rings should be a good fit in the grooves. Not tight but not loose.

Basically, check each part separately.
 
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nkaminar said:
The things that can cause the lock up are: Tight rod bearing, tight piston, tight rings, or bent rod. Here is what to do:


  • Loosen the bolts on the rod to see if that helps. If it does then take out the rod and piston and bolt up the rod without the piston. If the rod then turns OK that would indicate that the rod is bent. Have all the rods checked for bend, twist, and parallel ends.
  • Take the rings off the piston and put the piston in the bore to see if it is tight in the bore. If so then measure the bore and piston to see what the problem is.
  • If the piston is OK then put the rings in the bore and press it down into the bore about 2 inches with the piston. That will align the ring with the bore. Measure the gap. The gap should be according to the instructions that came with the rings but about 0.012. Do this on all rings.
  • If the rings are OK and the piston is OK then put the rings back on the piston and put it in the bore without the rod attached. If it is tight in the bore then check the ring grooves for the proper depth. You can turn the rings around to check the depth or just push on the rings to see if they are then flush or below the diameter of the piston. Clean out any carbon in the grooves with an old broken ring. The rings should be a good fit in the grooves. Not tight but not loose.

Basically, check each part separately.
Click to expand...
Thank you! I’ll have to work through this list when I have time next!
 
You stated that it was locked up when you began. Perhaps if you can determine why it locked up that might give you something to go on. Given what has been discussed here, and my experience with rings (I have very seldom found rings that I needed to open up, especially on an engine that has not been rebored) I'd put a can of beer on a bent connecting rod. You should be able to eyeball how the rod slides into the cylinder and lines up with its journal. Unless it hits the journal dead center, you may have an issue.
 
Check the big end of the con rod, it could be hanging up on the radius of the thrust and the fillet of the crank pin.
 
JayJay said:
You stated that it was locked up when you began. Perhaps if you can determine why it locked up that might give you something to go on. Given what has been discussed here, and my experience with rings (I have very seldom found rings that I needed to open up, especially on an engine that has not been rebored) I'd put a can of beer on a bent connecting rod. You should be able to eyeball how the rod slides into the cylinder and lines up with its journal. Unless it hits the journal dead center, you may have an issue.
Click to expand...

I'm with JayJay on this. Pull that rod and have it checked for straightness by a machinist that knows rods. I bought an old rebuilt but never run engine and traced a very heavy drag to one cylinder, pulled the rod/piston assembly and a machinist found that the rod was nearly off by 0.020 inches! He bent it back into alignment and all was well.
 
Did you oil the cylinder wall(s) and/or the pistons, before installing the piston(s)?
 
If a person purchases a set of rebuilt con rods on exchange, they will have been checked for bend and length dimension before they rebabbitt. Shops that do this have the mandrels to mount the rod into in order to check for straightness and length dimensions. On Babbitt bearing blocks, it's really necessary for the rebuilder to have the crankshaft and cam in order to get everything to fit right. The good thing about this is that they don't have to use dimensions for available oversizes like a replaceable bearing shell motor. They can set them up for whatever the current dimension is since the new babbitt is machined to fit the journals.

The cams don't use babbitt but they can be sleeved. They like to wear at the rear journal on the early motors since they didn't have a good oil feed back there. There is a Ford service bulletin that has a procedure to drill a feed hole from the valve chamber floor to that journal bore.
 
rotorwrench said:
If a person purchases a set of rebuilt con rods on exchange, they will have been checked for bend and length dimension before they rebabbitt. Shops that do this have the mandrels to mount the rod into in order to check for straightness and length dimensions. On Babbitt bearing blocks, it's really necessary for the rebuilder to have the crankshaft and cam in order to get everything to fit right. The good thing about this is that they don't have to use dimensions for available oversizes like a replaceable bearing shell motor. They can set them up for whatever the current dimension is since the new babbitt is machined to fit the journals.

The cams don't use babbitt but they can be sleeved. They like to wear at the rear journal on the early motors since they didn't have a good oil feed back there. There is a Ford service bulletin that has a procedure to drill a feed hole from the valve chamber floor to that journal bore.
Click to expand...



The Service bulletin( May 1929) is on page 342 and 343. Has Pictures and diagrams.

But IF camshaft block diameter has been wearing for 90 years it will need "re-sleeved".

When I checked my 89,000 mile 1929 block the camshaft and # 3 block bore in 1989 they were both worn to point where re-sleeving would be needed.
 
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