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MG MGB Technical - Piston Removal

Has anyone come up with an easy to way to remove non circlip pistons from the con rods, so the pistons and rods can be used again!??

Thanks

colin
Colin Parkinson

Set it up in the press with the boss section nicely supported with a mandrel to suit the shape of the piston in that area, put a little pressure on then with the rod over one way, warm the top of the rod a little as high up in the piston as possible with a blowtorch (not the oxy set) and the pin will press out easy peasy--it doesn't take much heat to make a big difference
The little bit of heat helps to release the rod's grip on the pin--They're not over tight anyway but best to make it easy
One thing that interests me--if you're going to reuse them ,why dismantle them, if they're ok better off left alone as It's one less time the rods have to be heated for reassembly
willy
William Revit

Willy, I am taking off +.030 which are really good. Unfortunately the only block I have left is going to +.060!

Colin
Colin Parkinson

It's one less time the rods have to be heated for reassembly. Willy
The problem with this method of fitting the pistons is you don't know how tight the fit is in the rod when it cools down, I know you should have a fit that requires a minimum force of 12lbs/ft on the nut used on the tool to pull the pin in, but by heating you don't know, and with new pistons and pins, made in somebody's garden shed in India or China, well something to think about,
Andy Tilney

Andy
First of all we don't use pistons and rods from tin sheds anywhere------------do we
Personally I prefer to hone the rods to sliding fit and run circlip pistons on later MGBs if it's going to be regularly dismantled
Many moderns have run press fit pins for several years and if heated properly with a natural heat there isn't an issue
If the rod is slightly warmed as suggested on removal it prevents damage to the inside bore of the rod and the pin, although, for the price of them one would always use a new pin

12ft/lb sounds a bit light on, depends on the tool I guess

As far as the,"but by heating you don't know"
comment--measure it before starting and don't overheat----normal workshop practice
willy
William Revit

I use a press to insert the pins - rod cold but piston hot.

Not happy if it needs less than 2 tons on the gauge.
Chris at Octarine Services

All good, -I go the other way, freeze the pins overnight and heat the rods in the warmer-then push the pin in with my fingers and centre it up, you get about 8-10 seconds to get it in place --personal choice but I think it's easier on the pistons, specially if they're something special or a wierd shape and can't be pressed against safely
William Revit

Actually I am using circlip pistons on the rods. So little end bushes or machine out to suit the pin?

Colin
Colin Parkinson


Road car- machine the rod out and fit bushes

Race- hone the rod for a sliding fit and run the pin straight in the rod

For either you need an oil hole straight down in the top of the rod with a nice flare on top to feed oil to the pin
Some engine people drill the oil holes up from the bottom, but in my opinion this method doesn't lube the pin properly, better from the top with a grooved bush

willy
William Revit

Willy not sure of the logic of fitting bushes or not, with bushes in a road car, but not race. Can you try and explain that? Surely it would be the same for both?

Totally get the oil feed hole!
Colin Parkinson

Colin-
In my opinion--

100%- bushed for the road as the bush will either have oiling grooves to hold some lubricant and/or bronze/brass which needs minimal lubrication

For racing,-keep it simple, the pin can be run straight in the rod as there is heaps more oil being thrown around to keep it lubed up and also the engine is regularly dismantled and inspected so any problem can be rectified---versus a road car that might do 100,000 before it comes apart
I wouldn't run the pin straight in the rod on a roady simply because of the lube issue with lower revs-race mod.only

Hope this answers your questions
Either way the rods need to be done properly by a machine shop and finished off with something like a Sunnen hone-any good engine shop should have the gear for the job

willy
William Revit

Colin

If your rod ends are in good condition, the simple answer would be to fit your circlip pistons up as press fit in the rods still and leave the circlips out

willy
William Revit

x 2 with willy - just press fit the pins
Chris at Octarine Services

Willy I have been away for a few days and only just seen your reply you posted on the 21/08/18, having just read it I think you have completely misunderstood what I was trying to say, let me be a bit clearer in my comments,
1. if you have a rod from an 18V engine and you heat that rod up to fit a new pin, when that has cooled down, how do you know what is the fit of that pin, how do you tell if it is tight enough when its cold, unlike using to special tool for this job where the fit is constantly measured during the whole fitting process, I know some manufacturers do use this method to fit there pistons, but we are talking BL-18V last comment, in the past I have fitted some press fit piston to a range of BL cars that have failed the BL fitting process, and the action for this was a fit new rod,if I had of heated the rod up, I would not have known that this fit was incorrect, if you don't have access to the correct tools, the other option is as Chris says using a press, at least that way you can see what force is needed to fit them, and yes I have seen a pin move in an engine when the fit is incorrect,
Andy Tilney

Andy
No' I didn't miss your point and if you want to go that way and check your fit that way, that's fine
Personally I'm a bit of a measurer and always have been
I also have seen pins move(not mine)--but if everything measures up right and the correct heat is used with frozen pins there isn't a chance of failure
William Revit

Willy Thanks for your reply,I think it is best if we agree to disagree, on this one, as you say what ever you are happy with that's fine,
Andy Tilney

Cheers Andy
My final word on this is--
To press a pin in cold is ok but there are problems with that as well--
If the piston has nice square machined internal pin bosses there isn't a problem but most pistons have tapered bosses on the inside to allow for the withdrawl of the piston former when they are being made and although some look square inside, if they haven't been machined they will be tapered and ideally either need machining or a wedge fitted while pressing
A gudgeon pin needs 1-1.5 thou interferance fit--any thing else gets either honed or converted to a bush
Cheers
willy
William Revit

I have made a decision. I am using circlip pistons, and have had the rods honed out to have a nice slide fit on the gudgeon pin. Drilled oil hole through the top of the little end.

By the way this is for a fast road engine, which will probably do no where near 5000 miles a year!!!!

Thanks for everyone's help and advice.

Colin
Colin Parkinson

This thread was discussed between 18/08/2018 and 01/09/2018

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