Rebuilt Engine Too Tight

[wdlanning]

Re-assembling L3350. Had the crankshaft main and rod journals machined. Rods machined .4 mm and mains to .2mm. Used assembly lube. I doubled checked the oil clearance and it’s in spec on the tight. Side. I could turn the crank by hand. However when I installed the rods/pistons and torqued to spec, I have to use a power pole to turn over the engine. This doesn’t seem normal.
my question is will it loosen with more hand turns? What’s the fix? Hone rod bearings?

 

[GeoHorn]

I hope you didn’t re-install the main bearing caps in different positons/orientation.…(or the rod-caps.). That’s what. it sounds like… (BTDT)

 

[Roadworthy]

Did you set the proper gap on the piston rings? Did you check the clearance on rod and main bearings? I believe Plastigauge still exists for this purpose.

 

[007kubotaguy]

It will not get looser. Check the rods. They should move on the crankshaft side to side. If they don't you may have a bent rod. Did you bore the engine ? Was the ring end gap checked ? How was bearing clearance checked ? When you say you could turn the crankshaft by hand how easy was it ?

 

[lugbolt]

I don't use assembly lube, it's way too "stiff" and causes things like this. Makes the engine hard to turn over. I have my own lube, about 2 teaspoons of trans fluid (type F!!) mixed with a quart of 10w40 or whatever it handy. Just my own preference, it helps dupicate actual running conditions (thinner than assembly lube).

If crank turns good without the pistons/rods, then there is an issue. What's the ring gap? Oil ring stacked? What's the rod bearing clearance? Rod caps on correctly (bearing tangs on same side)? Wristpins tight? Did you have any trouble getting the piston assemblies into the cylinders?

There is always some drag on the rings, in other words the rings are the greatest amount of parasitic drag inside of a piston engine (hence why automotive engineers keep making them thinner and thinner). When you put one piston assembly into the block and tightened the rod cap, did it turn over easier? second one make it really hard to turn? Third one? It'll be somewhat 'normal' for the crank to be harder to turn with the pistons properly installed, but "harder" is subjective. After building a few I know when one isn't quite right but if you don't do it much, you don't get "the feel".

 

[wdlanning]

I hope you didn’t re-install the main bearing caps in different positons/orientation.…(or the rod-caps.). That’s what. it sounds like… (BTDT)

They were marked and installed same position

 

[wdlanning]

I don't use assembly lube, it's way too "stiff" and causes things like this. Makes the engine hard to turn over. I have my own lube, about 2 teaspoons of trans fluid (type F!!) mixed with a quart of 10w40 or whatever it handy. Just my own preference, it helps dupicate actual running conditions (thinner than assembly lube).

If crank turns good without the pistons/rods, then there is an issue. What's the ring gap? Oil ring stacked? What's the rod bearing clearance? Rod caps on correctly (bearing tangs on same side)? Wristpins tight? Did you have any trouble getting the piston assemblies into the cylinders?

There is always some drag on the rings, in other words the rings are the greatest amount of parasitic drag inside of a piston engine (hence why automotive engineers keep making them thinner and thinner). When you put one piston assembly into the block and tightened the rod cap, did it turn over easier? second one make it really hard to turn? Third one? It'll be somewhat 'normal' for the crank to be harder to turn with the pistons properly installed, but "harder" is subjective. After building a few I know when one isn't quite right but if you don't do it much, you don't get "the feel".

 

[wdlanning]

Lug bolt ,all good questions
The problem is definitely with the rods. Pistons installed easily and move freely with rod on journal but not tighten. There is lateral movement on journal when slightly tightened but none when torqued. When I confirmed the oil gap before installing crank, it was difficult to move. When measured and used plastigauge the gap was a little over .0015. Spec is .00098-.00343.
With each additional rod installed the ability to turn crank decreases even with a power bar. This can’t be right.

 

[wdlanning]

Lug bolt ,all good questions
The problem is definitely with the rods. Pistons installed easily and move freely with rod on journal but not tighten. There is lateral movement on journal when slightly tightened but none when torqued. When I confirmed the oil gap before installing crank, it was difficult to move. When measured and used plastigauge the gap was a little over .0015. Spec is .00098-.00343.
With each additional rod installed the ability to turn crank decreases even with a power bar. This can’t be right.

I verified again that pistons installed correctly and rod caps match and face injection pump

 

[wdlanning]

It will not get looser. Check the rods. They should move on the crankshaft side to side. If they don't you may have a bent rod. Did you bore the engine ? Was the ring end gap checked ? How was bearing clearance checked ? When you say you could turn the crankshaft by hand how easy was it ?

Engine was not bored and ring gap was in spec. I measured rod bearing and journal and also used plastigauge. Before installing rods I could turn the crank over several times by hand without tools. A little tight but I attributed it to the assembly lube.

 

[DustyRusty]

I would start removing bearing caps and pushing the rods out of the way and try turning the crankshaft to see if it was a particular rod that is causing the problem.

 

[lugbolt]

One would be very surprised how many times I've seen plastigage cause engine failure. Because of that I do not use it, ever. Too many ways to mess up using it. Inside/outside micrometer and/or dial bore gauge. But that's just me. Everyone does stuff different.

One thing you can do. Take a rod cap off, and coat the bearing with dykem (spray ink). Then reinstall, and rotate engine in one direction only. Remove the cap and look at the wear pattern in the ink. It should be dead center. If not, the rod is bent and/or the crankshaft has a problem (tapered journal, twisted, etc). Repeat for the other rods. While you are inspected the rods, look closely at the bearings. If there is any foreign material at all between the bearing and the journal, the bearing will show it as a scratch. If all that is ok, and your clearances are 100% verified (again I don't trust plastigage), everything is square, not tapered, out of round, or twisted (did anyone check any of that?), What's left?

 

[GeoHorn]

The problem with rotating poorly-fit bearings/caps is that the rotation …intended to diagnose…. causes damage to the bearings, journals, and shafts. … which are now damaged because fitment was not properly determined before assembly.

 

[Joisey]

One would be very surprised how many times I've seen plastigage cause engine failure. Because of that I do not use it, ever. Too many ways to mess up using it. Inside/outside micrometer and/or dial bore gauge. But that's just me. Everyone does stuff different.

One thing you can do. Take a rod cap off, and coat the bearing with dykem (spray ink). Then reinstall, and rotate engine in one direction only. Remove the cap and look at the wear pattern in the ink. It should be dead center. If not, the rod is bent and/or the crankshaft has a problem (tapered journal, twisted, etc). Repeat for the other rods. While you are inspected the rods, look closely at the bearings. If there is any foreign material at all between the bearing and the journal, the bearing will show it as a scratch. If all that is ok, and your clearances are 100% verified (again I don't trust plastigage), everything is square, not tapered, out of round, or twisted (did anyone check any of that?), What's left?

I agree. A SLIGHT bit of oil on any of the parts, parts that are too warm from sitting in the sun, or mishandling of the plastigage will give you a false reading. A GOOD inside and outside micrometer is what is needed for accurate measurements, which should be performed at least every 90 degrees on the part to check for out of round and/or taper.

 

[kubotafreak]

No body mentioned it, but the rods must also move freely side to side on the small(piston end). Something to check before dropping them in cylinder. Sounds to me you have debris somewhere if the clearances are good. You will know as soon as you remove caps which was the culrprit. The bearing will have a rub/groove. Or you have bent rods… need more info on failure mode causing rebuild.

 

[kubotafreak]

Lug bolt ,all good questions
The problem is definitely with the rods. Pistons installed easily and move freely with rod on journal but not tighten. There is lateral movement on journal when slightly tightened but none when torqued. When I confirmed the oil gap before installing crank, it was difficult to move. When measured and used plastigauge the gap was a little over .0015. Spec is .00098-.00343.
With each additional rod installed the ability to turn crank decreases even with a power bar. This can’t be right.

What torque did you use when measuring out the assembly? Vs when assembled? The statement that the crank was tight isn't something most would say… the only tightness would be a slight increase in starting torque when using assembly lube. I use redline which will exhibit this, bit spins freely once started. When a short term build just use 40 weight.