Big end overhaul

Singles, twins and fours.
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simon.holyfield
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Big end overhaul

Postby simon.holyfield » Mon May 25, 2020 7:09 pm

Chaps, is it feasible to split a single big end in the home workshop? I don't have a press, but I can weld, make tools and I have a small lathe, two vices...
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'78 CX500
http://ariel-square-four.blogspot.com

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paul.jameson
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Re: Big end overhaul

Postby paul.jameson » Mon May 25, 2020 9:08 pm

I know of several people who have done this, but I have not done it myself - yet.
Paul Jameson
36 4G, 37 VH, 54 KH(A), 75 Healey 1000/4, 52/53 ex ISDT KHA (project).
Former Machine Registrar & Archivist, General Secretary and Single Spares Organiser (over a 25 year period).
Now Archivist once more - but not Machine Registrar.

nevhunter
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Re: Big end overhaul

Postby nevhunter » Tue May 26, 2020 12:37 am

It's one of the most critical parts of an engine. The parallel pins are the most difficult to get right as their actual fit is crucial to the success of the operation. Truing and balancing is best done by those who specialise in it. The running clearance of the rollers has to be within a few tenths of a thou and they must be the highest quality rollers all from the same source. NO variation of dimension. Nev

david.anderson
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Re: Big end overhaul

Postby david.anderson » Tue May 26, 2020 4:29 am

Simes
A press makes things easy. The Parallel fit pin is only .0015” interference fit, so it is not too difficult to part the flywheels without a press. It can be done with a series of bolts cut to various sizes that are put between the flywheels and the nuts are undone to force the flywheels apart. Alternately 4 steel wedges can be placed opposite between the wheels and pressed together with strong G cramps, or progressively driven in with a hammer. A hammer on the end of a brass drift on the end of the crankpin also helps the process. The taper pins are easier to part in that as soon as there is initial movement the flywheels will part whereas the parallel fit pin must be pressed/forced all the way.
Before fitting the new parallel fit crankpin ensure the sharp shoulder that first enters the flywheel is removed (spin in the lathe and bevel lightly with a file)) from either end of the pin otherwise as you press the pin back in it can shave metal from the flywheel and the flywheel is then rubbish that will never align perfectly. The flywheels can be pressed together in a good vice. Fully torque the side of the bigend that has the locating pin. And only minimal torque on the other nut. Align the rims of the flywheels with a steel ruler. When that is done place flywheels between lathe centres and use a dial gauge on the shafts against the wheels. The total runout of both shafts added together should not exceed .002”. The flywheels are best moved into alignment by dumping the part tightened side of the flywheel on the floor, while holding the shafts.
David

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adrie.degraaff
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Re: Big end overhaul

Postby adrie.degraaff » Tue May 26, 2020 5:24 am

Looking at your list you are talking WNG 350cc, in that case a brass hammer and a sliderule will do.

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simon.holyfield
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Re: Big end overhaul

Postby simon.holyfield » Tue May 26, 2020 6:19 am

Many thanks guys. Yes Adrie, I am of course talking about my W/NG.

I retire next week, and DIY projects permitting it's time to schedule having a look at the W/NG engine.
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'78 CX500
http://ariel-square-four.blogspot.com

nevhunter
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Re: Big end overhaul

Postby nevhunter » Tue May 26, 2020 7:09 am

A lot of this stuff was easier to assemble when new when all tapers are in good shape and you are using genuine Parts. If there's any rock in any taper or ovality from fretting it makes a good job hard or impossible to achieve. . Nev

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simon.holyfield
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Re: Big end overhaul

Postby simon.holyfield » Tue May 26, 2020 8:55 am

Easy question guys - what diameter are the flywheels?
cheers

Simes

'51 Square Four,
'58 Huntmaster,
'42 W/NG,
'78 CX500
http://ariel-square-four.blogspot.com


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