47 replies to this topic

[Inno]

I guess if you're read Vizard you already know Inno conrods are stronger than standard rods with extra strengthening ribs in there. If you're not building a full on race engine I'm not sure I would bother with lightening them. All you risk is making them weaker, getting them all balanced will probably gain you the same without the risk. 

that is true....I have Inno conrods but searching and reading a lot what many wise man wrote here and at other places I came to the conclusion that actually any Mini conrod is good enough for up to 100HP for engine that rews up to 6500 - 7000 (not for race) and even for much stronger turbo engines with lower CR and lower RPM.

 

A+ conrods are already light enough and more than we may need for 99% of non-race builds.

Inno conrods are stronger and can be lightened all the way to A+ size and still will be stronger than we need.

A conrods are heavy but stronger than A+ and again if carefully checked, lightened with good balance, finish and polishing are stronger than we may need and are far from the weakest engine point especially if used with ARP bolts and that is my plan.

 

I will start working on two sets of conrods, one Inno and one pre A+ and plan to make them similar in size and weight - at around 680grams. As said before it is more my personal target than may be a real need. Will use good bolts and do not see any chance they may be a weak point.

 

MED is lightening A+ conrods to 620grams and they are still reliable - do not plan to go anywhere near that (also have a set of A+ conrods but will only balance them and use for my third build).

 

I think that Crankshaft is more critical part than conrod - and plan to work a lot on it too - so that may be a bigger challenge   .

Edited by Inno, 14 May 2019 - 05:47 PM.

[Inno]

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

[Spider]

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

 

1.8895 - 1.8860"

[Inno]

 

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

 

1.8895 - 1.8860"

 

Thanks a lot!!

[Spider]

Thanks a lot!

I just left two sets fo conrods at machine shop to be checked (big/small ends and lenght).
I would appareciate if somebody can share small and big end diameter for 1275 ... it is not Mini specialised shop so it may be better if I give them exact diameters...

 

Big End Tunnel Size I've posted above.

 

Little End is 0.8108 to 0.8117 however, what you also need to check (and more importantly) is the size of the Gudgeon Pins you are going to use and check that against the Little End size. Interference needs to be in the range of 0.0008 to 0.0015". The pressure - cold - when fitting the pin also needs to be checked, all the way in. I have a 'tonnage' figure for this (not to hand) but the factory tool works on a thread and is used with a torque wrench and using this, the lubed torque needed to fit the pin must exceed 16 ft/lb.

 

There is nothing you can do about the big ends.

 

There is not much you can do about the little ends.  They are meant to be .03mm smaller than the gudgeon pin.

 

There is nothing you can do about the length.

 

If they aren't bust, don't fix them.

 

On the contrary,,,,

 

The Big Ends can be re-sized and re-shaped (if out of round) by Closing and Honing.

 

Little Ends, yes, there's nothing that can be done with them if they are out of spec.

 

Length - likewise, they can be shortened, by Closing and Honing.

 

I think Con Rods are something that tends to get over looked as part of an engine overhaul. They all need to be checked (even new ones) and there's much that can go wrong with them and can also be corrected.

 

The other items to check are the bolt spot facings, the fit of the bolts, the Big End side clearances, twist, bend and on it goes.

[unburntfuelinthemorning]

The other items to check are the bolt spot facings, the fit of the bolts, the Big End side clearances, twist, bend and on it goes.

 

What to you mean by bolt spot facings and how are they checked?

[Inno]

 

The other items to check are the bolt spot facings, the fit of the bolts, the Big End side clearances, twist, bend and on it goes.

 

What to you mean by bolt spot facings and how are they checked?

 

just wanted to ask .....

[Inno]

 

Thanks a lot!

I just left two sets fo conrods at machine shop to be checked (big/small ends and lenght).
I would appareciate if somebody can share small and big end diameter for 1275 ... it is not Mini specialised shop so it may be better if I give them exact diameters...

 

Big End Tunnel Size I've posted above.

 

Little End is 0.8108 to 0.8117 however, what you also need to check (and more importantly) is the size of the Gudgeon Pins you are going to use and check that against the Little End size. Interference needs to be in the range of 0.0008 to 0.0015". The pressure - cold - when fitting the pin also needs to be checked, all the way in. I have a 'tonnage' figure for this (not to hand) but the factory tool works on a thread and is used with a torque wrench and using this, the lubed torque needed to fit the pin must exceed 16 ft/lb.

...it means Gudgeon pins shall be 0,0008 to 0,0015" wider than Little end size?.....my machine shop said they will heat little end s to press in pins?!?

Shall I ask cold press with those tolerances?

[DeadSquare]

@ Moke   ...   You are correct, I didn't make myself clear.  A big end can be closed and honed, but unless you are very lucky and the correction is minimal in a longer rod, you can't do anything to one big end, without doing it to all of them, whether it is shaping or shortening.

 

I also agree, that rods are checked at an overhaul, but an inspection of the pistons and the shells is a good indication of a problem.

[Spider]

...it means Gudgeon pins shall be 0,0008 to 0,0015" wider than Little end size?.....my machine shop said they will heat little end s to press in pins?!?

 

 

Shall I ask cold press with those tolerances?

 

Yes, The Pin must be between 0.0008 and 0.0015" bigger in diameter than the Little End diameter.

 

In my books, the Pins must be cold presses and the Little End never heated. The reasons for this are many;- How much heat can be put in to the Little End before there's a loss of temper in the Rod ? After the Rod cools, how do you know if the Pin has been 'griped' tight enough? Heating the Rod hot enough to allow for a drop in fit of the Pin will cause distortion of the Rod - there is no question over this as that is what it is being heated for in the first place - to distort the little end big enough to get the Pin in !

 

Any Rods I have come in that show signs of having been heated go in the bin. Even if all the above was done satisfactorily, how does one know if the signs of heat (usually colour) are from either fitting the Pin or from a running issue? I've seem way to many issues from fitting Pins by heating the Rod to know it's a no - no.

 

Granted, some other brands of engines, this is the normal practice for fitting the Pins, however, the factory advice on how it's done with these is very specific. BMC / Leyland / Rover specifically advise against heating the Rod and advise the use of their tool or any other means of fitting them cold where the fitting pressure can be monitored all the way.

 

 

 

What to you mean by bolt spot facings and how are they checked?

 

The Spot Facings are the faces that the Bolts / nuts land on. They need to be checked that they are not worn, are smooth, perpendicular (perfectly so) to the Rod Bolt Hole, and that there's sufficient chamfer on them that the Bolt Head will seat correctly. If you look under the head of these Bolts, there's a radius between the Shank and The Head, you want the Heat to seat not the Chamfer. All small details but some that go towards a reliable long lasting engine.

[Inno]

 

...it means Gudgeon pins shall be 0,0008 to 0,0015" wider than Little end size?.....my machine shop said they will heat little end s to press in pins?!?

 

 

Shall I ask cold press with those tolerances?

 

Yes, The Pin must be between 0.0008 and 0.0015" bigger in diameter than the Little End diameter.

 

In my books, the Pins must be cold presses and the Little End never heated. The reasons for this are many;- How much heat can be put in to the Little End before there's a loss of temper in the Rod ? After the Rod cools, how do you know if the Pin has been 'griped' tight enough? Heating the Rod hot enough to allow for a drop in fit of the Pin will cause distortion of the Rod - there is no question over this as that is what it is being heated for in the first place - to distort the little end big enough to get the Pin in !

 

Any Rods I have come in that show signs of having been heated go in the bin. Even if all the above was done satisfactorily, how does one know if the signs of heat (usually colour) are from either fitting the Pin or from a running issue? I've seem way to many issues from fitting Pins by heating the Rod to know it's a no - no.

 

Granted, some other brands of engines, this is the normal practice for fitting the Pins, however, the factory advice on how it's done with these is very specific. BMC / Leyland / Rover specifically advise against heating the Rod and advise the use of their tool or any other means of fitting them cold where the fitting pressure can be monitored all the way.

Thanks...will let them know.....is there any special tool needed or well equipped machine shop shall have it?

 

 

 

What to you mean by bolt spot facings and how are they checked?

 

The Spot Facings are the faces that the Bolts / nuts land on. They need to be checked that they are not worn, are smooth, perpendicular (perfectly so) to the Rod Bolt Hole, and that there's sufficient chamfer on them that the Bolt Head will seat correctly. If you look under the head of these Bolts, there's a radius between the Shank and The Head, you want the Heat to seat not the Chamfer. All small details but some that go towards a reliable long lasting engine.

 

Does it means that there shall be a space at the top end of the hole to accommodate the radius part between the Shank and the Head....so the radius can sit in that space and allow Bolt head to seat correctly at the chamfer?   Sorry for my ignorance...so many details and even new terms since English is not my first language.

I will stress chamfer and that to machine shop and check it afterwards since I can't do that precisely enough in my garage.

Edited by Inno, 15 May 2019 - 04:32 AM.

[Spider]

Here's a sketch of a spot facing on the Main Body of a (1275) Rod and if it's not done or is not perpendicular this shows the issue (ignore the washer of course)

 

 

Of course, there's also Spot Facings on the Caps

 

 

This one, while not A Series, does show the contact area when the Facing becomes worn and why they need to be checked and corrected.

 

 

> Inno - Your Machine Shop should have the right gear to fit the Pistons to the Rods. No doubt, they'll have a Rod Heater, however, insist that this not be used for the reasons above (and the additional info below).

 

 

Some additional info, courtesy ACL, from tests regarding the heating of little ends to fit pins and why it should not be done;-

 

[Inno]

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)?

[DeadSquare]

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)?

 

I can understand how someone can easily heat the little ends to about 109C in a boiling concentrated common salt solution, but not how they can judge a 150-200 heating.

 

Classic Mini gudgeon pins have been cold pressed into little ends for 50 years !

 

If they are that ignorant of what to do, I'd be far more worried about what tools they are going to use.

 

The correct tool has a radius that matches the radius of the piston to minimise any damage to the skirt.   ...  By passing a screw through the pin and either into the tool or through the tool and tightening it, the pin is drawn through the little end.

 

It is vital that when pulling the pin through the little end at room temperature, the the torque needed to rotate the screw falls above a certain level, which for a Cooper S is 2.21 Kg m.

 

If the little end is heated  and the pin is not the same temperature, there is no way of knowing if the pin should have been gripped tightly enough to stop it migrating sideways and damaging the side of the bore.

 

This is not a case of laying the piston on an anvil and hitting it with a sledge hammer.

 

I do not wish to be unkind, but you are trying to needlessly "re invent a wheel" that has been working very well in a classic Mini engine and other cars for a very long time.

 

Provided that the pin and the little end have been at the same temperature for 1/2 hour and when measured are within the manufacturer's figures. DON'T ALTER THEM.

[Inno]

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)?

 
I can understand how someone can easily heat the little ends to about 109C in a boiling concentrated common salt solution, but not how they can judge a 150-200 heating.
 
Classic Mini gudgeon pins have been cold pressed into little ends for 50 years !
 
If they are that ignorant of what to do, I'd be far more worried about what tools they are going to use.
 
The correct tool has a radius that matches the radius of the piston to minimise any damage to the skirt.   ...  By passing a screw through the pin and either into the tool or through the tool and tightening it, the pin is drawn through the little end.
 
It is vital that when pulling the pin through the little end at room temperature, the the torque needed to rotate the screw falls above a certain level, which for a Cooper S is 2.21 Kg m.
 
If the little end is heated  and the pin is not the same temperature, there is no way of knowing if the pin should have been gripped tightly enough to stop it migrating sideways and damaging the side of the bore.
 
This is not a case of laying the piston on an anvil and hitting it with a sledge hammer.
 
I do not wish to be unkind, but you are trying to needlessly "re invent a wheel" that has been working very well in a classic Mini engine and other cars for a very long time.
 
Provided that the pin and the little end have been at the same temperature for 1/2 hour and when measured are within the manufacturer's figures. DON'T ALTER THEM.

In this case I may have a small problem. I do not tend to reinventing anything just sharing what have around and asking for advices.....and happy when I can get it.

I need to find solution...if someone has a picture of the tool would
be great to post it so I get idea what do I need. I may purchase it and see how to do that.....just thinking shoul have gone with floating pins and pistons....

Machine shop is actually very big and equiped with dozens of different machines and they do a lot for last 40 years....but there is no big (or any) demand for machining Mini engines...