K-Series 18K4 Piston Conrod Disassembly and Fitting Technique

Lovel · 13th September 2012, 07:05

Outline of how to reuse your existing conrod and fit a new piston.

The Conrod LFF000410 and Piston in this particular example is from a 1.8 Turbo engine, this model has a slightly shorter conrod and a different piston compared to the standard NASP models.

Given that there are no circlip retainers to hold the gudgeon pin into the piston, the k-series gudgeon pin is a tight fit in the conrod in order to limit movement of the pin.

Unless the correct hydraulic press or tooling is available when removing the gudgeon pin the piston and/or conrod will be irreparably damaged. In most cases it probably does not matter if the piston gets damaged as it may be changed out anyway in the majority of cases.

Yenmak liners and pistons were used on this occasion, but I have carried out the same process with Goetze liners and AE/Nurall OE pistons too. The quality of the Yenmak parts are every bit as good as the OE supplied in my opinion.

1. First step is to carefully cut the piston crown and sides in half with a hacksaw avoiding marking the top of the conrod with the saw blade and inducing stress cracks.

2. Remove cut halves exposing gudgeon pin.

3. Using a deep 21mm socket I pressed the gudgeon pin out with my trusty vice and a little persuasion from a 1 3/4lb hammer.

4. Eventually the pin will require another socket to push the pin out fully.

5. Clean out the conrod small end and observe for any nicks or damages that may hinder the fitting of the new gudgeon pin.

6. I am led to believe that the factory rods were induction heated in an automated process. However for me this means I have to heat the small end up just enough until the temper colour starts to appear and no more than that. Any higher a temperature and you risk annealing the conrod.

7. Place the piston quickly over the top of the hot conrod and insert the pre-oiled gudgeon pin inserting quickly in to the small end and ensure that the pin is through far enough. You only get one chance at this so ensure that everything is in place. Note that I used a 6mm anchor bolt fixing to hold the gudgeon pin more securely. Note the direction of the arrow on the piston crown needs to point to the front of the engine. Also note that each conrod is numbered at the big end for each cylinder and these numbers also face the front of the engine.

Note the original damaged piston

mh007 · 13th September 2012, 07:17

Excellent workaround if you haven't got access to a press.

I'm fortunate to have always had one but this is great.

marinabrian · 13th September 2012, 07:19

Nice how to Gary, did your replacement pistons come complete with new gudgeon pins or did you reuse the originals?
Brian

Lovel · 13th September 2012, 07:22

Quote:

Originally Posted by marinabrian

Nice how to Gary, did your replacement pistons come complete with new gudgeon pins or did you reuse the originals?
Brian

Came with new gudgeon pins too, already fitted with rings, ready to go apart from fitting to the conrod of course.

marinabrian · 13th September 2012, 07:40

Quote:

Originally Posted by Lovel

Came with new gudgeon pins too, already fitted with rings, ready to go apart from fitting to the conrod of course.

Sounds good Gary, I'm reusing S/H pistons and liners where the big ends had "spun" and the rods from my original engine.
The pistons have already been removed in the same fashion as you described, the good pistons were removed from the U/S rods by drilling into the little end with a spot weld drill to relieve the stress on the gudgeon pin then pushing it out without damage to the piston.
My concerns related simply to removing the gudgeon pins from the rods without damage, to facilitate their reuse.
I'll post some pictures later

Brian

rover54 · 13th September 2012, 08:32

Wouldn't putting the gudgeon pins in the freezer overnight also help with assembly, less heat needed on the conrod small end.

Lovel · 14th September 2012, 11:36

Quote:

Originally Posted by marinabrian

Sounds good Gary, I'm reusing S/H pistons and liners where the big ends had "spun" and the rods from my original engine.
The pistons have already been removed in the same fashion as you described, the good pistons were removed from the U/S rods by drilling into the little end with a spot weld drill to relieve the stress on the gudgeon pin then pushing it out without damage to the piston.
My concerns related simply to removing the gudgeon pins from the rods without damage, to facilitate their reuse.
I'll post some pictures later

Brian

How much material had to be removed to get them free. I would have thought the pins would be pretty hard to machine

Lovel · 14th September 2012, 11:38

Quote:

Originally Posted by rover54

Wouldn't putting the gudgeon pins in the freezer overnight also help with assembly, less heat needed on the conrod small end.

I'm would think that cooling the pins down would help marginally, but the most expansion you get will be from heating the conrod as per the factory method.

marinabrian · 14th September 2012, 21:58

Quote:

Originally Posted by Lovel

How much material had to be removed to get them free. I would have thought the pins would be pretty hard to machine

Sorry Gary, I drilled two holes adjacent to one another through the casting of the little end of the rod, which was enough to relieve the tension on the gudgeon pin and enable them to be pushed out easily.
You are absolutely right in thinking the gudgeon pins would be to hard to machine

My pistons weren't as bad as the one is your picture, at least three weren't however after removing the rings and inspecting the skirts, the top compression ring groove had been slightly expanded, so I decided not to reuse them.
Just out of interest how much were your piston sets ?
And I couldn't find any problem with your emailed excel file, would I be right in thinking you were utilising a Discovery II key

Brian

Lovel · 14th September 2012, 22:51

Quote:

Originally Posted by marinabrian

Sorry Gary, I drilled two holes adjacent to one another through the casting of the little end of the rod, which was enough to relieve the tension on the gudgeon pin and enable them to be pushed out easily.
You are absolutely right in thinking the gudgeon pins would be to hard to machine

My pistons weren't as bad as the one is your picture, at least three weren't however after removing the rings and inspecting the skirts, the top compression ring groove had been slightly expanded, so I decided not to reuse them.
Just out of interest how much were your piston sets ?
And I couldn't find any problem with your emailed excel file, would I be right in thinking you were utilising a Discovery II key

Brian

The Yenmak piston and liner set were £230, pretty good value when you see them in the flesh, I was sceptical of their quality at first, but once seen you can tell they are good. I also priced up the original fittment pistons and liners but they were £430 for a set, so I thought would give the Yenmaks a go this time instead of AE/Nurall/Goezte.

Trechii sell the Yenmaks for £230/set
Lymmengineparts.co.uk sell the OE AE/Nurall/Goetze liners for around £430/set

The key I was trying was from a 75. In fact I have tried a couple of other 75 keys with same results with only half the barcode being correct

13th September 2012, 07:05	#1
Lovel I really should get out more....... P6B, L550, Imp, F56, Commando Join Date: Nov 2006 Location: Aberdeenshire Posts: 2,886 Thanks: 352 Thanked 677 Times in 440 Posts	K-Series 18K4 Piston Conrod Disassembly and Fitting Technique Outline of how to reuse your existing conrod and fit a new piston. The Conrod LFF000410 and Piston in this particular example is from a 1.8 Turbo engine, this model has a slightly shorter conrod and a different piston compared to the standard NASP models. Given that there are no circlip retainers to hold the gudgeon pin into the piston, the k-series gudgeon pin is a tight fit in the conrod in order to limit movement of the pin. Unless the correct hydraulic press or tooling is available when removing the gudgeon pin the piston and/or conrod will be irreparably damaged. In most cases it probably does not matter if the piston gets damaged as it may be changed out anyway in the majority of cases. Yenmak liners and pistons were used on this occasion, but I have carried out the same process with Goetze liners and AE/Nurall OE pistons too. The quality of the Yenmak parts are every bit as good as the OE supplied in my opinion. 1. First step is to carefully cut the piston crown and sides in half with a hacksaw avoiding marking the top of the conrod with the saw blade and inducing stress cracks. 2. Remove cut halves exposing gudgeon pin. 3. Using a deep 21mm socket I pressed the gudgeon pin out with my trusty vice and a little persuasion from a 1 3/4lb hammer. 4. Eventually the pin will require another socket to push the pin out fully. 5. Clean out the conrod small end and observe for any nicks or damages that may hinder the fitting of the new gudgeon pin. 6. I am led to believe that the factory rods were induction heated in an automated process. However for me this means I have to heat the small end up just enough until the temper colour starts to appear and no more than that. Any higher a temperature and you risk annealing the conrod. 7. Place the piston quickly over the top of the hot conrod and insert the pre-oiled gudgeon pin inserting quickly in to the small end and ensure that the pin is through far enough. You only get one chance at this so ensure that everything is in place. Note that I used a 6mm anchor bolt fixing to hold the gudgeon pin more securely. Note the direction of the arrow on the piston crown needs to point to the front of the engine. Also note that each conrod is numbered at the big end for each cylinder and these numbers also face the front of the engine. Note the original damaged piston

13th September 2012, 07:17	#2
mh007 This is my second home MG ZT260 SE, MG ZT190+, MG ZTT 160, R75 Conn SE 2.0, R75 Conn SE 2.5 X 3, R75 Club SE 1.8, P5B Coupe Join Date: Jul 2009 Location: Keynsham, Bristol Posts: 4,211 Thanks: 65 Thanked 635 Times in 499 Posts	Excellent workaround if you haven't got access to a press. I'm fortunate to have always had one but this is great.

13th September 2012, 07:19	#3
marinabrian MG ZT Join Date: Jan 2011 Location: Newcastle Upon Tyne Posts: 20,151 Thanks: 3,565 Thanked 10,837 Times in 5,718 Posts	Nice how to Gary, did your replacement pistons come complete with new gudgeon pins or did you reuse the originals? Brian

13th September 2012, 08:32	#6
rover54 Retired rover 75 v6 Auto Conn. SE 54 plate LPG and 2006 Rover 75 v6 Auto LPG , 1.8 r75 Manual Join Date: Aug 2010 Location: London Posts: 3,379 Thanks: 0 Thanked 6 Times in 6 Posts	Wouldn't putting the gudgeon pins in the freezer overnight also help with assembly, less heat needed on the conrod small end.