47 replies to this topic

[DeadSquare]

 I expect Moke will be able to bring up a drawing on here, I don't know how to do it.

 

The tool is used for taking pins out as well as replacing them.

 

I made my own.

[Spider]

Thanks a lot Moke...all clear now.

 

I just had discussion in the machine shop and guy insisted to heat it just a bit ......he said it is heated to 150 to 200 degreec Celsius max, just to facilitate easier penetration of the pin and to avoid possibility of making any damage during totally cold pressing.....of course he said he is 40 years in a business and never had any problems with that light heating treatment....he said they can do cold press but there may be a risk of damaging something....as I said before my area is very limited with machine shops and this one is apparently the best and also the only one doing unleaded valve seats and stuff like that....and non has any experience with Mini engines (beside few random customers within last 20 years).

 

If I insist on a cold press shall I machine small ends to lowest tolerance to facilitate easier press.....I just measured one conrod and pin and pin is 0,034mm wider than the hole. That is still at the upper tolerance but it will be harder to press it in than if it is at lower tolerance (may be just above 0,02mm)?

 

My concern here is as I've already mentioned and Deadsquare has raised - in particular, they or you - will have no way of knowing how tight the pin is in the rod after fitting. The method is not recommended by BMC / Leyland / Rover.

 

This is the basic tool

 

 

and how it's fitted for removing and refitting the Pins

 

 

A, B and C are all 0.032"

 

The procedure goes over a few pages, but the final foot note is this

 

 

and what the Factory is getting at here, is that the grip of the rod on the pin must be checked all the way and if the torque needed is less than 16 ft / lb the Rod must not be used.

 

I don't actually have this tool, but a Rod cradle that allows me to hold the rod by the little end and press the Pins in and out. While I do this, I monitor the pressure gauge on the press and I do them cold. I do apply some light grease (the Factory recommends Graphite Oil for this) to the Pin before fitting, just so it doesn't pick up on the rod.

 

 

Another way around all this is to have the Little End in the Rod honed to give 0.0002 - 0.0005" clearance (that's 0.2 to 0.5 of a thou). Then the Pin will be a slip fit by hand. To retain the pin in position, make up some Teflon Buttons to go in the end of the Pins. Most performance Engines that I've built, I have done this as a matter of course to.

[Spider]

I found this article on Con Rod Reconditioning. The pictures aren't brillient,but it does cover some of the aspects of it.

 

http://what-when-how...ing-automobile/

[Inno]

I found this article on Con Rod Reconditioning. The pictures aren't brillient,but it does cover some of the aspects of it.

 

http://what-when-how...ing-automobile/

Moke I owe you a lot thanks!!

 

I do not think I will be able to change mindset of a guy who is probably well over 70 and claims it must be heated - and he doesn't have proper tool....so I may construct the tool for myself.

 

I have a set of extra gudeon pins that I already machined to be 0.01mm smaller than the small end to have them for dry build - I can use them for the tool. I need adapter body and strong screw that fits inside diameter of Gudeon pin...guess can be machined from something - just need piston radius to fit the adapter - guess can use the same adapter radius for all 1275 pistons.

Sounds nice to be less dependent on machine shop...

[Inno]

 

 

Another way around all this is to have the Little End in the Rod honed to give 0.0002 - 0.0005" clearance (that's 0.2 to 0.5 of a thou). Then the Pin will be a slip fit by hand. To retain the pin in position, make up some Teflon Buttons to go in the end of the Pins. Most performance Engines that I've built, I have done this as a matter of course to.

 

Is this mean that I make floating pins from standard pins and instead of a metal ring to secure the pin at both ends I use Teflon Buttons?

What kind of buttons? where I can find Teflon for that and what is the shape?...practically those buttons are crabbing cylinder walls? Can they wear out? Or be pushed bu Pins too hard?

 

Can that work on a high mileage road engine?

[mini13]

yo have to make the teflon buttons to fit your pins and bore size, as the bore of the pis ( and taper ) comes up different sizes between manufacturers, also they need to sit close to the bore so they cant turn and escape, specially on slipper pistons.

 

http://www.paeco.com...ins&Buttons.htm

[Spider]

Inno, as well put by Mini13 ^ you'll need to make some buttons or work from some like in that great link he kindly included. I bought a few lengths of Teflon a few years back and am still working my way through that ! It turns OK (similar to most plastics).

 

I've found the Pin Bores, between piston manufacturers does vary a lot. You'll also find with the modern wasted skirt pistons the pins are well short enough to be able to fit a decent button head in there.

 

If you go down this route, the buttons do need to be a neat fit in the pins and they should also be vented. I do this with an off-set angled hole. The hole on the head of the button you do want off-set so as it contacts the bore it doesn't seal off.

 

I believe the Air Cooled VW Engines all have buttons as standard as do many motorcycle engines.

[Inno]

yo have to make the teflon buttons to fit your pins and bore size, as the bore of the pis ( and taper ) comes up different sizes between manufacturers, also they need to sit close to the bore so they cant turn and escape, specially on slipper pistons.

 

http://www.paeco.com...ins&Buttons.htm

thanks

[Inno]

 

Is there any exact value for 1275 conrod inner diameter (1,75" crank journal size)?

 

1.8895 - 1.8860"

 

I got my 9 conrdos from the machine shop and all holes (big and small) are almost perfectly round (0.5 thousands max oscilation) and length within less than a thousand of inch.

All small ends are 20,61mm (+/-0,01mm) = 0,8114" - sounds perfect right in the middle of tolerances

 

But...

 All big ends are the same 48,16mm (+/-0,01mm) = 1,8965" and max given radius is 1,8895 meaning all 9 conrods are exactly the same with big end 0,007" wider than higher tolerance!?! - I may call my project Bond, James Bond...

 

is it possible there is also another acceptable dimension of the big end?

[Spider]

 

 

Is there any exact value for 1275 conrod inner diameter (1,75" crank journal size)?

 

1.8895 - 1.8860"

 

I got my 9 conrdos from the machine shop and all holes (big and small) are almost perfectly round (0.5 thousands max oscilation) and length within less than a thousand of inch.

All small ends are 20,61mm (+/-0,01mm) = 0,8114" - sounds perfect right in the middle of tolerances

 

But...

 All big ends are the same 48,16mm (+/-0,01mm) = 1,8965" and max given radius is 1,8895 meaning all 9 conrods are exactly the same with big end 0,007" wider than higher tolerance!?! - I may call my project Bond, James Bond...

 

is it possible there is also another acceptable dimension of the big end?

 

 

I have to reference sources for these figures and to be sure there wasn't an error, I just checked them both again now and they both have the same figures. They are also the same figures that I use. I believe them correct.

 

 

(I've posted this chart as it has imperial and metric figures)

 

At 0.007" difference here, I would respectfully suggest that there's been a measurement error.

 

Another way this can be 'checked' for measurement error is to fit a set of new shells to the Rod, torque them up, then let off one side and check how far the Cap springs open. You should be able to fit a 0.003 to 0.005" feeler gauge in here. This is the Bearing Nip and is another critical measurement, it is what actually holds the shells fast in the Rod and prevents them from spinning in the Rod. It is not a substitute for measuring the Rod Tunnel, as you could have the correct Nip (or Crush) but it could be out of shape (which yours appear to be). If you can measure this 'Nip' figure, then again, I would suggest that there's been a measurement error.

 

Given that the bearing clearances here are 0.0010 to 0.003", ovality (which I think is what you are meaning by 'oscilation' ?) of 0.0005" (1/2 a thou) is pretty big, it's 50% of the lower end clearance. It does show some distortion in the rods and that they need correcting.

 

I also doubt - from factory - that all 9 rods would be within 0.001" in length - you may have gotten lucky, but over 9 rods, I seriously doubt that. I would expect to see up to 0.003" variation between them.

[r.tec]

...some basics I came around on the net concerning the topic: https://www.fsb.uniz..._Nitriranje.pdf

[Inno]

...some basics I came around on the net concerning the topic: https://www.fsb.uniz..._Nitriranje.pdf

thanks...that is from the University in my home town....

[Inno]

 

 

 

Is there any exact value for 1275 conrod inner diameter (1,75" crank journal size)?

 

1.8895 - 1.8860"

 

I got my 9 conrdos from the machine shop and all holes (big and small) are almost perfectly round (0.5 thousands max oscilation) and length within less than a thousand of inch.

All small ends are 20,61mm (+/-0,01mm) = 0,8114" - sounds perfect right in the middle of tolerances

 

But...

 All big ends are the same 48,16mm (+/-0,01mm) = 1,8965" and max given radius is 1,8895 meaning all 9 conrods are exactly the same with big end 0,007" wider than higher tolerance!?! - I may call my project Bond, James Bond...

 

is it possible there is also another acceptable dimension of the big end?

 

 

I have to reference sources for these figures and to be sure there wasn't an error, I just checked them both again now and they both have the same figures. They are also the same figures that I use. I believe them correct.

 

 

(I've posted this chart as it has imperial and metric figures)

 

At 0.007" difference here, I would respectfully suggest that there's been a measurement error.

 

Another way this can be 'checked' for measurement error is to fit a set of new shells to the Rod, torque them up, then let off one side and check how far the Cap springs open. You should be able to fit a 0.003 to 0.005" feeler gauge in here. This is the Bearing Nip and is another critical measurement, it is what actually holds the shells fast in the Rod and prevents them from spinning in the Rod. It is not a substitute for measuring the Rod Tunnel, as you could have the correct Nip (or Crush) but it could be out of shape (which yours appear to be). If you can measure this 'Nip' figure, then again, I would suggest that there's been a measurement error.

 

Given that the bearing clearances here are 0.0010 to 0.003", ovality (which I think is what you are meaning by 'oscilation' ?) of 0.0005" (1/2 a thou) is pretty big, it's 50% of the lower end clearance. It does show some distortion in the rods and that they need correcting.

 

I also doubt - from factory - that all 9 rods would be within 0.001" in length - you may have gotten lucky, but over 9 rods, I seriously doubt that. I would expect to see up to 0.003" variation between them.

 

I measured big ends and unbelievably got same values as machine shop on all big ends - 1,8965 ....got a bit more difference in length. I have limited accuracy measuring equipment so I will visit another machine shop for additional more accurate measurement.

[Spider]

 

I measured big ends and unbelievably got same values as machine shop on all big ends - 1,8965 ....got a bit more difference in length. I have limited accuracy measuring equipment so I will visit another machine shop for additional more accurate measurement.

 

 

Just one point that perhaps I omitted here. In order to measure these, the threads on the studs need to be lubricated and the nuts torqued up. Be absolutely sure that the mating faces of the cap & rod are surgically clean before fitting together.

 

They won't take up the right size or shape until torqued up.

[Inno]

 

 

I measured big ends and unbelievably got same values as machine shop on all big ends - 1,8965 ....got a bit more difference in length. I have limited accuracy measuring equipment so I will visit another machine shop for additional more accurate measurement.

 

 

Just one point that perhaps I omitted here. In order to measure these, the threads on the studs need to be lubricated and the nuts torqued up. Be absolutely sure that the mating faces of the cap & rod are surgically clean before fitting together.

 

They won't take up the right size or shape until torqued up.

 

They were far from torqued up (probably squeezed bit stronger than with a hand (still strange how similar they all are)......will do it tomorrow...can' wait...thanks a lot!!!!