Exceptionally Tight Big End Pins?

[MikeDodd]

Hi everyone,

I wanted to pick the collective brain here to see if anyone had come across this and has any suggestions.
Rebuilding a crank with new bearings/rods/big end pins (rod kit is TKRJ brand) and welding it up as we go. Got one side trued up nice and easily to within 0.02mm without too much trouble. However, the other side just doesn't want to play ball. I've tried gentle heat, bigger hammers, swinging it harder etc etc.... It has moved a little, but it's still sitting around 0.5mm of runout (so I'm out by a factor of 10! ).

Anyone got any tips/tricks that they've had work in a similar situation? freeze spray on the pin? Press apart and use a little emery paper on the pin and/or flywheel (I'm a little bit wary of trying this approach)? Press apart half way & true then press together & hope like hell it doesn't move too much?

I've got a bunch of ideas that should work in theory - just after some suggestions people have had work for them

Thanks in advance
Mike

 

[AUTOMAN]

Tight big end or not true?

pick one, if ya going to pick

were the pins/rods measured?

rephrase the question

 

[MikeDodd]

As the title says, one big end is exceptionally tight. Therefore I cannot budge the flywheel in relation to the pin in order to true it.

I just thought I'd ask if there was any assistance anyone could provide from personal experience. I've trued cranks before so i know what chasing your tail feels like with crank true. This one just isn't moving at all.

 

[AUTOMAN]

aye mate,
pin into crank press fit!

confused the issue with new rods/bearings

measures?

 

[Jan_P]

Agree with Mr Automan I would be nervous the pin is to large affecting bearing play ..

 

[Jim]

Disclaimer: it's been well north of 30 yrs since I pressed a crank apart and back together. Having said that...

" Press apart half way & true then press together & hope like hell it doesn't move too much?"

I think that's what I'd try first. Half the pin means half the friction. Shouldn't be too hard to true up and then press fully back together. And since the force is straight down on the cheek and pin, it shouldn't really move out of alignment. If it does, it'll be very slight and you should be able to beat that back out of it.

You using a 5 lb lead hammer?

 

[MikeDodd]

Disclaimer: it's been well north of 30 yrs since I pressed a crank apart and back together. Having said that...

" Press apart half way & true then press together & hope like hell it doesn't move too much?"

I think that's what I'd try first. Half the pin means half the friction. Shouldn't be too hard to true up and then press fully back together. And since the force is straight down on the cheek and pin, it shouldn't really move out of alignment. If it does, it'll be very slight and you should be able to beat that back out of it.

You using a 5 lb lead hammer?

Thanks Jim,
Yeah that was my thoughts too the longer I've been thinking about it - any movement when pressed back together should be small and hopefully can correct it. At the very least I'm no worse off than when I started haha.

Will give that one a go i think and see how it plays out.

Have been using mainly a big ass ball pein steel hammer with a nice big wide brass drift to ensure no damage to the cheeks, but have also trialed an 8lb steel hammer with the drift still with no luck.

 

[MikeDodd]

Agree with Mr Automan I would be nervous the pin is to large affecting bearing play ..

Thanks Jan, I'm not too concerned about that - the rod/pin/bearing all come as a set and bearing play was good. I've found them to be a decent manufacturer, have used their rod kits before. It's more just the fit of one pin into the outer cheek that is seemingly tight. Will give Jim's solution a go and report back how it plays out.

 

[Signal]

Could you have forgotten the assembly lube on that side?

 

[Its been a long time]

I'd be measuring the bore and pin before applying more force. There's a reason it's so tight and I have found over the years that simply applying more force without understanding the reason why is often a bad idea.

 

[MikeDodd]

Could you have forgotten the assembly lube on that side?

Sorry Signal, the issue isn't that the big end pin is tight on the bearing it's tight in the crank cheek (I can see how my title was misleading though!!)
I'm assuming that you are referring to assembly lube in the big end bearing rather than between the pin and cheek!

 

[MikeDodd]

I'd be measuring the bore and pin before applying more force. There's a reason it's so tight and I have found over the years that simply applying more force without understanding the reason why is often a bad idea.

Yeah totally agree with you there, I've reached the level of force that I'm comfortable with. I was just putting the feelers out to see if anyone else had experienced this issue before.

 

[Its been a long time]

Yeah totally agree with you there, I've reached the level of force that I'm comfortable with. I was just putting the feelers out to see if anyone else had experienced this issue before.

Better that you know the facts of what you're dealing with. 0.02mm too much interference there will give you a headache.

 

[Signal]

orry Signal, the issue isn't that the big end pin is tight on the bearing it's tight in the crank cheek (I can see how my title was misleading though!!)
I'm assuming that you are referring to assembly lube in the big end bearing rather than between the pin and cheek!

I did mean assembly lube on the crank pin before it is pressed into the crank wheel. I was taught to do this to stop the pin galling.

 

[AUTOMAN]