34 replies to this topic

[Spider]

I found this really informative thread here with this info but just wanted to double check.

 

In the above post it also talks about Piston to Rod fitting process and states that the pins should be cold pressed on and definitely not heated. When discussing how the pins are fitted, machine shops that I have talked to here have said that they heat up the small end?

What is the correct process?

 

Thanks 

 

It's pretty well covered in that thread in the link.

 

Heating the little end, when the manufacturer says otherwise, is a butchers method of fitting pins.

[JonnyAlpha]

 

I found this really informative thread here with this info but just wanted to double check.

 

In the above post it also talks about Piston to Rod fitting process and states that the pins should be cold pressed on and definitely not heated. When discussing how the pins are fitted, machine shops that I have talked to here have said that they heat up the small end?

What is the correct process?

 

Thanks 

 

It's pretty well covered in that thread in the link.

 

Heating the little end, when the manufacturer says otherwise, is a butchers method of fitting pins.

 

 

Interesting

[JonnyAlpha]

Big end tunnel bore diameter is 1.8955 to 1.896"

Small end, simply measure the piston gudgeon pin diameters. The small end of the Conrod must be a minimum of 0.0008" smaller.

As regards fitting, I use the heating method. However if you don't know what you are doing overheating will soften the steel.

Ac

 

Do you mean 0.0008" larger? 

[GraemeC]

No, smaller. It’s an interference fit.
Hence the use of heat to expand the rod

[Cooperman]

Moderate heating should cause no issues. This can be combined with putting the gudgeon pins in a deep freeze for 24 hours before fitting, which slightly shrinks them.

[grizzler73]

I

 

 

I found this really informative thread here with this info but just wanted to double check.

 

In the above post it also talks about Piston to Rod fitting process and states that the pins should be cold pressed on and definitely not heated. When discussing how the pins are fitted, machine shops that I have talked to here have said that they heat up the small end?

What is the correct process?

 

Thanks 

 

It's pretty well covered in that thread in the link.

 

Heating the little end, when the manufacturer says otherwise, is a butchers method of fitting pins.

 

 

Because of this faffing around and the difficulty in getting good rods I have gone over to H beam rods with floating pins for my race build, The rods are £200 and that includes the bolts (ARP 2000) These bolts are a lot 

cheaper to replace too. I really hate the idea of heating up critical items! I did the dry build over the weekend and it all fitted together beautifully!

[JonnyAlpha]

No, smaller. It’s an interference fit.
Hence the use of heat to expand the rod

 

Aha - ok

[JonnyAlpha]

So I have just been in the garage having a go at measuring the Conrods with my new Micrometer Set and Telescopic gauges.

 

Starting with Conrod No 4 I measured the Small End, taking measurements in line with the rod (1) and then at 90 degrees (2)

(1) 0.8112"

(2) 0.8114"

 

So that falls inside the required 0.8108 to 0.8117.

 

Now for the Big End the first measurement (1) is top to bottom in line with the rod, I then took two more measurements, diagonally at about 22 degrees either side of vertical, these readings are a little concerning?

 

(1) 1.8953

(2) 1.8964

(3) 1.8957

 

All of these are over the figure of 1.8895 - 1.8860" for a crank journal of 1.75".

 

This gives a deviation of 1.1 thousandth of an inch between (1) and (2) and 0.4 thousandth of an inch between (1) and (3).

 

All of the above of course is subject to my ability to (a) take an accurate measurement and (b) read the Micrometer correctly

 

I'll update later.

Edited by JonnyAlpha, 23 September 2019 - 12:51 PM.

[ACDodd]

Measure your gudgeon pins, use thes as the reference for the small end tolerancing. Measure your rods at 90 degrees from the parting line as well.

Ac

Edited by ACDodd, 23 September 2019 - 12:46 PM.

[haz]

I had this problem on my build yeas and years back on a couple of rods (there's a thread on here actually). I went down the heat and cool route.

 

Put the offending rods on the radiator for a couple hours. Put the bolts in the freezer. Went together a treat.

[JonnyAlpha]

So some interesting results:

 

This is my first time using a Micrometer so, hopefully, the readings I have taken are incorrect

WRT the gudgeon pin, the small end needs to be a minimum of 0.0008 smaller, but what is the maximum?

 

Anyway I am going to take the rods to the only pace locally that (may) re-size rods and ask them to measure them to check with a view to seeing wether they need re-sizing.

 

Here are the first stab at measuring:

 

[ACDodd]

I think you need a second opinion.

Unlikely to have a small end at 0.8168"

Ac

[JonnyAlpha]

OK so I have been out in the garage tonight revising on how to use a telescopic gauge and micrometer and re-did the measurements.

 

Big Ends 

 

Rod 4 - (1.8956), (1.8963), (1.8953 )

Rod 3 - (1.8951), (1.8957), (1.8954)

Rod 2 - (1.8959), (1.8955), (1.8957)

Rod 1 - (1.896), (1.8958), (1.8965)

 

The first measurement is 90 degrees to where the rod joins, the next two are diagonally across the big end.

 

I think my measuring is getting better and all bar the ones in red are within tolerance? 

 

I am still having trouble measuring the small end, I think it maybe because of using such a small gauge anyway, here are the measurements:

 

Small Ends

 

Rod 4 - 0.8128 (0.0002), 0.8122 (-0.0004)

Rod 3 - 0.811 (-0.0016), 0.8122 (-0.0004)

Rod 2 - 0.8124 (-0.0002), 0.8118 (-0.0008)

Rod 1 - 0.8119 (-0.0007), 0.811 (-0.0016)

 

The first measurement is in line with the rod and the second is at right angles to the rod.

The figures in brackets are the differences to the measurement of the gudgeon pin which I have measured at 0.8126"

Looks like I need to try the small end measurements again, 0.8128 can't be right as I tried the gudgeon pin in all of the rods and it would slide through

Edited by JonnyAlpha, 24 September 2019 - 08:44 PM.

[Hpal]

Because of this faffing around and the difficulty in getting good rods I have gone over to H beam rods with floating pins for my race build, The rods are £200 and that includes the bolts (ARP 2000) These bolts are a lot 

 

cheaper to replace too. I really hate the idea of heating up critical items! I did the dry build over the weekend and it all fitted together beautifully!

 

https://www.ebay.co....emis&media=COPY

Same as these ones?  I'm faced with the same dilemma, I can get some second hand a+ rods, but for a bit more I can have these new ones and I think they have very good reputation and feedback.  Tell me, does the pin float ie neat fit in both the rod and the piston? Or is it tight in the piston and pivots on the rod? Do you need teflon buttons to hold the pin in place? 

[nicklouse]

Because of this faffing around and the difficulty in getting good rods I have gone over to H beam rods with floating pins for my race build, The rods are £200 and that includes the bolts (ARP 2000) These bolts are a lot 

 

cheaper to replace too. I really hate the idea of heating up critical items! I did the dry build over the weekend and it all fitted together beautifully!

 

https://www.ebay.co....emis&media=COPY

Same as these ones?  I'm faced with the same dilemma, I can get some second hand a+ rods, but for a bit more I can have these new ones and I think they have very good reputation and feedback.  Tell me, does the pin float ie neat fit in both the rod and the piston? Or is it tight in the piston and pivots on the rod? Do you need teflon buttons to hold the pin in place? 

The ends will still need checking and sizing.