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Crank & flywheel balancing.

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binky Bill Blick (Disabled)
Disabled Account, Antarctica   ATA
In all fairness to the engine, the counterbalanced crankshaft IS mostly balanced when they were made. Cracked cranks on the XPAG XPEg is not from poor balancing of crank, it is from the engine design/ rod deflection. The engine does benefit from balancing the weight of the rod and piston assembly. If you want to pay to have crank balanced at a machine shop, that is just fine. A lot that can be done in the garage by a hobbiest with not real elaborate tooling. Rods that are not bent are always a plus in this engine, and it not hard to figure out how to check.

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Buckdendave David Hill
St Neots, Cambridgeshire, UK   GBR
1954 MG TF
True, but since they were made, several things will have changed - pistons, bolts and clutch cover at least. Certainly having mine balanced properly was well worthwhile. I did weigh the pistons and rods but decided they were close enough, but didn't keep a record. The only difference I noticed to the crank assembly when it came back from balancing was a large lump of metal welded to the clutch cover, which confirms comments made in a previous post. The important thing is to make sure the clutch cover is bolted up in the same orientation as it was balanced. I checked the con rods on a sheet of plate glass, which may not be the best way.
Dave H

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Steve S Avatar
Abingdon West, Southern California, USA   USA
In reply to # 3904482 by TD4834 For the nominal amount of money required to do a proper balance I’d leave it in the hands of a known shop. They have the equipment and tooling to perform the job to high standards and in a safely managed environment. A properly done balance job is especially important with regard to our engines. Although I commend the DIY spirit to take on such a project I don’t believe this an area where one should be taking financial shortcuts. It may come back to bite you should you come up wrong, your engine breaks and scatters itself on the floor. It doesn’t have to be a “race engine” to self destruct.

I agree with Bill, the more precise the balance act, the longer and smoother your engine will run. The rods should also be checked now and then for roundness and re-sized if necessary. This service usually includes lightening them so even though it's an easy job, may as well let the shop do that while they're at it.



Edited 1 time(s). Last edit at 2019-03-07 04:12 PM by Steve S.

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binky Bill Blick (Disabled)
Disabled Account, Antarctica   ATA
Dave the sheet of glass is OK. Not to get overly complex, but to further check rods you mount them (4) on a "shaft" so the caps can be tightened down with shells in place. Then you check to see that all 4 are parallel. generally on such an engine with deflection known to be an issue, a replacement schedule for new shells is advised. Following such a schedule of shell replacement, it always a good idea to keep each rod exactly where it was.

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Mikelead Mike Leadbeater
York, Yorks, UK   GBR
1953 MG TD
Lots of good advice, crank definitely out of balance so will get the shop to do this, too much to do to start making my own balancer . I will have a go at checking and balancing the flywheel and clutch as this should be easier to do statically.

Made a ring gap grinding jig from a chunk of ally, using a resin bonded diamond wheel on a small lathe, can post a pic if anyone interested, once set up it will keep the ends dead square.

I will also make a rod jig to check roundness and straightness, should be easy to clock on my Miller.

All good fun, must get back to the tub rebuild.

Cheers

Mike

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plus4moggie Tom Lange
Bar Harbor, ME, USA   USA
I love trying to do things myself, for the first time. But there are some times I realize that the job I have done or considered doing is best left to the experts. Balancing moving engine parts is one of them, as is re-bushing carb bodies and installing new butterflies on new shafts.

Here is what my machine shop does to balance my parts, AFTER all machining, checking and trueing and lightening of flywheel has been done:

Rods: Balance for total weight, and balance end for end to 1 gram accuracy.
Pistons: balance to within 1 gram
Crank - spin on crank balancing machine to balance within 1 gram
Flywheel - bolt to crank, and balance to 1 gram (only goes on crank 1 way)
Clutch cover - attach to flywheel and crank, balance by either drilling out metal or welding on metal; mark flywheel and clutch cover to re-assemble in this position later

I don't waste my time trying to do any of this - they know best where and how to lighten a heavy piston, and how to both balance end for end and total weight. For me to balance any part of the crank arrangement I would need both a way of spinning, a way of knowing where it is light and heavy and by how much, and more brains than I have. If you take off too much weight in one place, for instance, your crank, pistons or rods will be grossly out of balance - it's not just about weight, but all about balance.

Sorry, that's why machinists have experience - to do this sort of thikng quickly, accurately and efficiently.

Tom Lange
MGT Repair



Edited 1 time(s). Last edit at 2019-03-07 05:21 PM by plus4moggie.

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  Steve S thanked plus4moggie for this post
Mikelead Mike Leadbeater
York, Yorks, UK   GBR
1953 MG TD
Thanks, Tom, for your words of wisdom.

Part of the fun of car restoration for me is making the tools and acquiring the skills to do as many restoration jobs as possible, I call it "Skill collecting", and, being a retired engineer, I have lots of experience in engineering and instrumentation, but, as you say some tasks are best given to the experts, although at a cost.

Checking the rods is easy on a milling machine using a dial indicator, I will post some photos of how I did this.

Cheers

Mike

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binky Bill Blick (Disabled)
Disabled Account, Antarctica   ATA
Not surprisingly, crank makers have always had the best crank balancing technology around.

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