16 replies to this topic

[babsbrown]

Evening guys,

As above really? I know the cranks typically get reground to the next bearing size e.g 10 thou 20 thou etc...

But at what stage of wear is indicative of a regrind? I have 5thou average of deviation from the standard 1098 size of 1.625. They're measuring 1.620" would that suggest a regrind is required?



Thanks, Babs

[Spider]

That definitely needs a grind.

 

Be sure to have it done in a grinder that holds the crank between chucks, not one of those rubbish Prince Chassis grinders.

 

Ask them to Index it while they have it up in the grinder.

[babsbrown]

That definitely needs a grind.

Be sure to have it done in a grinder that holds the crank between chucks, not one of those rubbish Prince Chassis grinders.

Ask them to Index it while they have it up in the grinder.

Thanks mate, to be honest there's only one place that does it near me. I'm not sure what machines they have I'll have to double check. They want £180 for the Job mind.

Pardon my ignorance but what does indexing mean please?

Cheers,

[babsbrown]

 20241115_100929.jpg   39.65K   10 downloads

 

This was the measurement i took 

 

 

[Spider]

Thanks mate, to be honest there's only one place that does it near me. I'm not sure what machines they have I'll have to double check. They want £180 for the Job mind.

Pardon my ignorance but what does indexing mean please?

Cheers,

 

If they do the job right then it costs what it costs. Engine reconditioning soon adds up !

Indexing is where they'll phase the crankpins to get them all truly at 0⁰ and 180⁰. The standard production tolerances can have them out from that.

 

PS the actual standard size of the Crankpins is 1.6254" to 1.6259".. The Mains are 1.7505" to 1.7510".

 

The measurement you have there looks like it's bang on 1.6250", though, that's only a measurement in one place. The 1098's I find wear more on the Mains than the Crankpins.
 

[babsbrown]

Thanks mate, to be honest there's only one place that does it near me. I'm not sure what machines they have I'll have to double check. They want £180 for the Job mind.

Pardon my ignorance but what does indexing mean please?

Cheers,

If they do the job right then it costs what it costs. Engine reconditioning soon adds up !

Indexing is where they'll phase the crankpins to get them all truly at 0⁰ and 180⁰. The standard production tolerances can have them out from that.

PS the actual standard size of the Crankpins is 1.6254" to 1.6259".. The Mains are 1.7505" to 1.7510".

The measurement you have there looks like it's bang on 1.6250", though, that's only a measurement in one place. The 1098's I find wear more on the Mains than the Crankpins.

Thanks mate, haha to be honest I haven't used a micrometer since engineering class at school haha. I measured the big ends and they're 1.7510. Maybe I can get away with a polish.
Cheers for the information im learning heaps as I build this engine.

[weef]

Before taking any mearurements you have to ensure your micrometer is calibrated and within spec.

Crankpins have to be measured for both taper and roundness, 

Generally 0.004" is the maximum undersize from the design minimum dimension, then a regrind to the next preferred journal size is required.

From your picture your measurement appears to be at the maximum limit, perhaps it may be worth getting your shaft measured at a machine shop.

[Mr Piggy]

5 thou is way too much wear and you'd have very low oil pressure. I'd regrind a crank that measured 0.001" under spec.

[ings]

After grinding, the crankshaft should ideally be hardened, as the grinding process reduces its hardness.

[sonscar]

And after hardening it you need regrinding to correct potential distortion?Not all steel is capable of meaningful hardening is my understanding.Just my thoughts,Steve..

[Spider]

These cranks aren't surface hardened at all.

 

You could have them tuftrided, however, there's no advantage in a road car.

[babsbrown]

Thanks guys after a bit of thinking I reckon I'll take it for a regrind.

[Earwax]

I would take the crank to your trusted machine shop, take your reference measurements and also ask them to check what their reference measures are. Then they will decide - this will hopefully avoid bearing spinning or a regrinding if unnecessary.

 

( I do not trust my micrometer readings on things like cranks and rods) ( PS do your conrods need closing?)

[babsbrown]

I would take the crank to your trusted machine shop, take your reference measurements and also ask them to check what their reference measures are. Then they will decide - this will hopefully avoid bearing spinning or a regrinding if unnecessary.

( I do not trust my micrometer readings on things like cranks and rods) ( PS do your conrods need closing?)

Thanks mate, I'm not sure what conrod closing is?

[Shooter63]

What Earwax means is big end re-sizing, where the machine shop grinds a small amount off the conrod thus allowing them to hone the big end back to the correct size for bearing fitment. Where abouts in the country are you? This will allow people to suggest decent machine shops.

Shooter