Tight Wrist Pins? = Too Tight?

[cunning plan]

So I bought a 1641 Barrel and Piston set, I cannot remember the brand, but it was not premium one. However, the wrist pins are extremely tight to get into the pistons, to the point that you have to use a rubber mallet with the piston laying on a block of wood on the workbench to get the pin in at all, installing it on the con-rod without breaking a component seems impossible as everything will be moving and the hammer will be swinging around. :character0036: :?

I am guessing that they are not supposed to be that tight? After watching some videos it appears that they should have a slight resistance, but be able to be pushed in using your fingers?

I assumed buying a kit, everything would match, obviously with it being a cheaper kit, I was wrong! :roll:

Do I need to go back to the engine machine shop?

:sign0009:

 

[atafonso]

First make sure the pins slide in the rod freely by hand.
The pins should be a push fit in the pistons at room temp. If you have a gas torch, heat gun or hair dryer, heat up the piston slightly around the pin area and the pin itself to simulate room temp. Oil the pin and the bore, then try to push with your fingers. If it doesn't go in at all, get a scotch brite fine pad and lightly polish the bore of the piston until it goes in by hand at room temp.

Abel

 

[cunning plan]

First make sure the pins slide in the rod freely by hand.
The pins should be a push fit in the pistons at room temp. If you have a gas torch, heat gun or hair dryer, heat up the piston slightly around the pin area and the pin itself to simulate room temp. Oil the pin and the bore, then try to push with your fingers. If it doesn't go in at all, get a scotch brite fine pad and lightly polish the bore of the piston until it goes in by hand at room temp.

Abel

I was hoping you would reply Abel :lol: arty0047:

I had not thought about the ambient temperature, I was doing it in the garage and I would guess it was 3-5 degrees in there at the weekend. Hopefully, as you say, that was too cold for the piston bores which made them too tight, probably only by 0.001mm, but enough to stop it going through easily.

I'll try again with a heatgun then!

While you are here Abel, I took a CC measurement of the heads and all the cylinders were 50ml apart from one which took 50.5 / 51ml, what do you think, will the 0.5 - 1ml make too much difference, or not enough to worry about? oke:

 

[atafonso]

You will be surprised how much of a difference the temp will make :shock: :lol:
What have you used to measure? If you using a seringe, it's hard to get accuracy of more than 1/2cc.
On a stock engine i wouldn't worry about 1/2 or 1 cc. If it was 2cc's then i would.
It could be that the head has been flycut, so you can make a simple test; place the two barrels on the cleaned surface of the head and use a straight edge on top of both cylinders. It should be perfectly flat. If you can see light between cylinders and edge, the heads have been flycut incorrectly and will leak and get loose. Solution is to either flycut again PROPERLY, or replace.
Hopefuly it will be ok

Abel

 

[cunning plan]

What have you used to measure? If you using a seringe, it's hard to get accuracy of more than 1/2cc.
On a stock engine i wouldn't worry about 1/2 or 1 cc. If it was 2cc's then i would.

Yes a seringe from one of those CC'in kits you can buy with the pre-cut plastic discs in. I did it three times to make sure and it seemed to take a little more than the other cylinders which were all 50cc, right on, but this one cylinder seemed to take just over 50, certainly not 52 though. :?

It could be that the head has been flycut, so you can make a simple test; place the two barrels on the cleaned surface of the head and use a straight edge on top of both cylinders. It should be perfectly flat. If you can see light between cylinders and edge, the heads have been flycut incorrectly and will leak and get loose. Solution is to either flycut again PROPERLY, or replace.
Hopefuly it will be ok

Abel

Like this?:

There is a slight 'nick' in the top of the cylinder from where I presume it dropped a valve or something got in there and damaged it years ago, so perhaps that is where the 0.5cc is going.

Hopefully as you say, it is a tiny variation in one cylinder that should make little to no difference.

Thank you Abel. arty0021: arty0047:

 

[atafonso]

What have you used to measure? If you using a seringe, it's hard to get accuracy of more than 1/2cc.
On a stock engine i wouldn't worry about 1/2 or 1 cc. If it was 2cc's then i would.

Yes a seringe from one of those CC'in kits you can buy with the pre-cut plastic discs in. I did it three times to make sure and it seemed to take a little more than the other cylinders which were all 50cc, right on, but this one cylinder seemed to take just over 50, certainly not 52 though. :?

It could be that the head has been flycut, so you can make a simple test; place the two barrels on the cleaned surface of the head and use a straight edge on top of both cylinders. It should be perfectly flat. If you can see light between cylinders and edge, the heads have been flycut incorrectly and will leak and get loose. Solution is to either flycut again PROPERLY, or replace.
Hopefuly it will be ok

Abel

Like this?:

There is a slight 'nick' in the top of the cylinder from where I presume it dropped a valve or something got in there and damaged it years ago, so perhaps that is where the 0.5cc is going.

Hopefully as you say, it is a tiny variation in one cylinder that should make little to no difference.

Thank you Abel. arty0021: arty0047:

Good God, you have some artistic talents :lol: :lol: :lol:
Exactly, check if there is a gap, if not, you're on the money :mrgreen:
If the head has a dimple, probably the acrilic won't seat flat, for that reason you might have the higher cc measurement.
Abel

 

[mike.s]

Warm them up with a heat gun and they`ll push in easy .

I bought a set of AA pistons and barrels recently - 3 pins would push in by hand, but one is having none of it. 30 seconds from the heat gun though and it slides in easily.

I have to say, i`m not that impressed with the quality off the AA pistons and barrel. Obviously, one pin is very slightly larger than the others, but worse, one of my barrels was actually oval and not round! I had my case machined for bigger barrels and 3 barrels would go in no problem, but the 4th would not go in any hole. I took it to my machione shop and he ended up turning it in the lathe to make it circular and fit in to the case.

I think i`ll pay the little bit extra next time for Mahle ones!

 

[cunning plan]

First make sure the pins slide in the rod freely by hand.
The pins should be a push fit in the pistons at room temp. If you have a gas torch, heat gun or hair dryer, heat up the piston slightly around the pin area and the pin itself to simulate room temp. Oil the pin and the bore, then try to push with your fingers. If it doesn't go in at all, get a scotch brite fine pad and lightly polish the bore of the piston until it goes in by hand at room temp.

Abel

You will be surprised how much of a difference the temp will make :shock: :lol:

Abel you sir are amazing.

As you advised, I heated the piston bore holes with a heat gun for 30 seconds or so and the wrist pins slid through perfectly, no axle play, real smoooooth. arty0021: arty0047:

Warm them up with a heat gun and they`ll push in easy .

I bought a set of AA pistons and barrels recently - 3 pins would push in by hand, but one is having none of it. 30 seconds from the heat gun though and it slides in easily.

I have to say, i`m not that impressed with the quality off the AA pistons and barrel. Obviously, one pin is very slightly larger than the others, but worse, one of my barrels was actually oval and not round! I had my case machined for bigger barrels and 3 barrels would go in no problem, but the 4th would not go in any hole. I took it to my machione shop and he ended up turning it in the lathe to make it circular and fit in to the case.

I think i`ll pay the little bit extra next time for Mahle ones!

Yes I looked at the branded box this time when I went back to work on the bus and they are AA as well. I think you are right, probably better to spend a little more for another brand, although, so far the AA ones I have are OK. :shadey:

 

[atafonso]

That's great, glad it worked well

I have been using AA's in mild builds with zero problems. The pistons IMHO are well built, they are always within 1g and measure well too. The cylinder's material seems to be of low quality, but never had any problems apart from small differences in measurement.
With the Mahle pistons, they are of a better quality overall but most times they come between 6-10g from each other making it impossible to balance properly without seriously compromising the pistons. Solution i found was to buy extra sets, then mix and match. Expensive exercise

Abel

 

[cunning plan]

That's great, glad it worked well

I have been using AA's in mild builds with zero problems. The pistons IMHO are well built, they are always within 1g and measure well too. The cylinder's material seems to be of low quality, but never had any problems apart from small differences in measurement.
With the Mahle pistons, they are of a better quality overall but most times they come between 6-10g from each other making it impossible to balance properly without seriously compromising the pistons. Solution i found was to buy extra sets, then mix and match. Expensive exercise

Abel

I forgot to weigh the pistons, but hopefully as you have found with AA, they should be within tolerance.

Also, that is interesting that you say the barrels can have small differences in measurement as it brings us nicely to the next issue:

http://forum.earlybay.com/viewtopic.php?f=4&t=76183

:lol: opcorn:

:sign0013: