Tight small ends

[d3c0y]

Hey Guys,

 

I just pulled an L28 apart and some of the rods feel a little tight to move left to right on the pistons, it's probably on half of them. What does this symptom indicate?

Bores still look good and the baring sheels dont show any major scrubbing. It looks like this engine was rebuilt pretty recently.

[garvice]

It needs new pins/bearings (pins probably bent), mentioned that and you said you were going with new pistons/rods anyway. Also size the new pistons off of the bore not the existing piston because there felt like there was some play in the piston (also some scuffing on piston which indicated piston was twisting as it went up and down). Also it was recently (in kms not time) rebuilt, but by someone who had no idea.

[d3c0y]

Yeah i ended up picking up an F54 which i ultimately wanted for $100, so i am going to build my race motor out of that. I was just thinking of putting this together for the interim to replace my L24 which is using shite loads of oil.

 

I was more wondering what common causes of the pins being tight are - like oil starvation or as you said bent pins.

Bent pins is pretty radical though. I reckon that siezing the little end bearing would be enough to scuff the skirts.

I guess i bent a crank once and the car still drove.

It's already got .040" pistons in it so thats bad news might need to hog it out to .120"!

 

You would think if the pistons were twisting on the way up that the crank bearings would have noticeble damage, they didnt look too bad though.

 

I couldnt find any evidence of welding on the crank snout either? The front keyway is bent quite badly though.

[madz]

Along with oil starvation, could detonation/pre ignition also be a factor with bent/seized pins...?

 

Just curious 

[Zedsabbath]

I'd be more concerned about the loose ones, under operating temperature the piston pin bores expand and that will make the loose ones even looser...If you can get movement out of the tight ones by hand, I'd leave them

 

The movement from left to right doesn't mean all that much, it's the rotational movement of the pin in the piston you should check, it should be fairly free without being so tight that you need a hammer to move the rod

 

It sounds like the engine wasn't fully run in

[garvice]

look too bad though.

Didn't look that good though either.

 

I couldnt find any evidence of welding on the crank snout either?

It was the harmonic balancer that was welded (Inside welded to outside, I.E. no take up in the harmonic balancer) which inturn killed the keyway and stuffed the main bearings. Don't think it would have helped the little ends either.

 

You notice the wear on the thrust bearings?

 

Along with oil starvation, could detonation/pre ignition

Oil pressure was always good, detonation was never an issue (tuned on a dyno by a respectable tuner who did a very safe tune).

 

it's the rotational movement of the pin in the piston you should check

The rods stood up in the piston by themselves.

 

d3c0y, you could try getting the pins out and see what the pins/bearings look like.

Also, why the jump from 40thou to 120thou? That is a big jump, surely you can get a piston in between?

[d3c0y]

Yeah i tried to get a pin out of one of them and couldn't using a quite significant amount of force.

You are right though the pistons should be binned and the crank and rods checked for damage.

 

I was putting the question out there out of interest just to learn a bit more about it more than anything, not going against what you said.

 

Thanks for clearing up that bit about the balancer - it had me guessing

 

Why bore it out? More HP 

[garvice]

I was putting the question out there out of interest just to learn a bit more about it more than anything, not going against what you said.

No worries, just figured I would clarify it for everyone so people were not jumping to conclusions.

Personally I think it all came down to someone rebuilding an engine without knowing exactly what they were doing.

 

Why bore it out? More HP 

Fair enough, can't argue with that. Just 120 thou is a big jump from 40thou

 

I was just thinking of putting this together for the interim to replace my L24 which is using shivere loads of oil.

If that is the reason, then there would be nothing wrong with just bolting it all back together with a new balancer and fixed keyway. It will not produce massive power but it wont burn "shivere loads" of oil. In fact it was good for a 100mph pass at the qtr mile when I was unknowingly running 7-10 degrees less timing than I thought (balancer wasn't even welded on straight). All depends what you mean by the phrase "Interim".