Morris Minor Owners Club

on my engine build, i have found one of the pistons broken so have got hold of a new set of rings and pistons. I have attempted to remove the con rods from the old pistons. Pictures of how i did it.
they were quite easy to remove in the scheme of things. However, i would like some advice on refitting the new pistons to the con rods please. I apparently have cooper 'S' rods (if that makes a difference.

My plan is to put the piston in a pan of boiling water and heat the small end of the con rod with either a 'map gas gun' or a heat gun. Would either be suitable? Would i damage the con rod if i used the naked flame option?

I can confirm that the conrods you have (AEG521) are Cooper S. There is no difference in fitting those rods to any other 1275cc pistons/conrods.

You will not get the small end hot enough with a heat gun for it to expand to allow the pin to slide in even with the pistons warmed up.
The big problem is that the conrod cools down very quickly because of its mass and there is the danger that the pin get held before it is in position.
I would advise that you get your local engine reconditioning company the fit the pistons.
I an not a fan of heating up the small end as if it gets too hot it can effect the molecular structure of the metal and lead to failure of the small end. Saying that many pistons are fitted using a oxyacetylene torch to warm up the small end.

hello Phil, dependable as usual.

Would an oxy torch not burn hotter than a map gas gun though? Seems youtube is full of video's of people doing this and just wondered if it really is that simple.

A oxyacetylene torch will produce more heat than a heat gun. That additional heat is required but extreme care must be taken.

The correct way of removing and fitting 1275cc 'A' Series piston pins is with the BMC/Churchill special tool which comprises of 18G537, 18G1150 & 18G1150A. See Morris Marina wksp manual for details.
The tool and its composite parts pulls the piston pin out of the rod to remove and again pulls the piston pin back into the rod to fit.
I have a similar version of the piston pin removal/fitting tool and its composite parts so I do not require to heat the small end of the rod when removing and fitting 1275cc pistons.

i've seen that tool in the marina manual Phil (good recommendation from yourself there) and recon i might be able to make something similar. If it invloves a long bolt and spacers, i will attempt it.

The option of a machine shop isn't possible at the moment as work/opening hours are a stumbling block.

If and when you have access to a machine shop/tools you can make a copy of the tool without too much difficulty.

i have access to a fly press, lathe and all the other machines as i work for an engineering company.

thats how i made the removal tool above

A lathe and possibly a welder is all you need so it looks good to go.
I will try and post photos of my piston pin removal tool later so as to give you some idea of what is required.
Phil

remembered another 2 questions.

I guess the pistons can go anyway around as they look identical?
is there any reason why you can't use normal 3/8" nylon lock nuts on the conrod bolts? Manual gives 2 torque settings for nylon and normal nuts.

ok phil, i've found a solution.
new piston with gudgeon pin being wound in. some old bits of thick rubber to protect the piston on one side.
i used a length of 12mm rod with various spacers and one of the old pins to give it that final push past the surface of the piston.
it can be done with no heat required.

i slowly wound it through the conrod, stopping every couple of turns to check it was going in straight and wasn't restricted. A good clean of the piston pin hole, pin and small end of the conrod. pin slid smoothly into the piston to start. I used a small amount of spray grease which i'll wipe off when i come to thoroughly clean the rod and piston before fitting the rings.

I have tried the piston in the bore WITHOUT rings and it fits fine and slots onto the crankshaft.

I have checked the piston gap in the bore and measured it at 0.012" so within tolerance.

I hope the rest goes ok.

Well done.
If the pistons are not marked 'FRONT' and do not have a split skirt the pistons they can be fitted either way round.
As regards the big end nuts - the nuts fitted to the 1275cc Cooper S and 1275cc Midget/Sprite conrod big end bolts are special high tensile Nylock nuts and should be used only once.
https://www.moss-europe.co.uk/nut-big-e ... soc=143946
Normal Nyloc nuts should not be used as they do not have the correct tensile strength for 1275cc big end applications.
Phil

thanks for that. i did suspect they were a special nut. off to moss europe i guess next week.

all pistons fitted to the conrods and now the pistons fitted to the block.

That is a fantastic solution to fitting gudgeon pins. Well done.

Well done! I was formulating a similar strategy for this job - great to see you nailed it. Great tip using the rubber, i would have ripped, shipped and busted my first piston without that idea