Cross Drilled Crank

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Cliffords
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Cross Drilled Crank

Post by Cliffords »

Hi
I am after a reasonable crank for my 912 engine . 2.2 LC
Its cross drilled . Preferably one that has not already been reground but let me know of anything you are aware of .

Thank you

David

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Hawaiis0
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Re: Cross Drilled Crank

Post by Hawaiis0 »

£1500 via QED
£650 via lotusbits
Nothing is fool proof. Fools are clever!

Cliffords
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Re: Cross Drilled Crank

Post by Cliffords »

That's not the current Lotusbits price , hence I am looking for an alternative .

Thanks for your reply

David

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Hawaiis0
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Re: Cross Drilled Crank

Post by Hawaiis0 »

Cliffords wrote:
Fri Apr 29, 2022 15:51
That's not the current Lotusbits price , hence I am looking for an alternative .

Thanks for your reply

David
yes sorry . that's a 2 litre one
Nothing is fool proof. Fools are clever!

Pete Boole
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Re: Cross Drilled Crank

Post by Pete Boole »

Do you want a cross-drilled crank so that you can run the plain lower bearing shells? If you plan on thrashing it it's worthwhile. If it's just going to be a "road car" doing low-ish mileage then grooved shells will still do many thousands of miles without any trouble. You could cross drill a standard crank - any machine shop should be able to drill four holes! I'm not sure if the cross-drilled factory cranks were made from stronger material to obviate the risks associated with cross drilling. Do you know?

Pete

Cliffords
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Re: Cross Drilled Crank

Post by Cliffords »

I was hunting for a cross drilled one as that's what came out , however you are absolutely correct I have built engines in the past with plain journals and grooved shells . It is looking harder to find than I thought . I may even end up with a plain one in the end . like yours ! :D

Oh and the stronger material , no I don't think so , cross drilling a plain crank so long as it was billet to start with is fine .

Pete Boole
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Re: Cross Drilled Crank

Post by Pete Boole »

Certainly on V8's hardly anyone uses cross-drilled cranks nowadays. I don't know what made Lotus change to cross-drilled cranks unless the flexibility of the bottom end was leading to problems with grooved shells. From what I understand the oil pump is more than adequate (apart from the turbo Esprits sometimes). Cross-drilling is all about increasing oil flow to the con rod big ends so maybe they were having big end failures? It's interesting! It's like a chicken-and-egg conundrum - did they change to cross-drilled cranks because they needed plain lower bearing shells or did they have big end problems that led to cross-drilled cranks that necessitated plain lower main bearing shells?!

Does anyone know the history here?

Pete

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Re: Cross Drilled Crank

Post by Cliffords »

Thanks to a member on here , actually two members were involved , I am now the proud owner of a replacement crank and so it off for a regrind next week. After a really detailed measure of the original and replacement last night we find they are pretty much the same size, and the original was on standard shells so that's great plenty of opportunity for a light regrind (10thou).

My next question is , on both cranks original and replacement the big end journals vary across the crank in size , i.e. they are not all the same size. The variation is significant about 8 thou from smallest to biggest . This is on both the cranks I am now comparing. So original grinding at factory was not too accurate it seems. The mains are consistent across both cranks .

To my question is the standard size of the mains and big end journals available anywhere ?

Many thanks

David

Pete Boole
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Re: Cross Drilled Crank

Post by Pete Boole »

Do you mean the bearing shells themselves? I believe they are lotus-specific - the reason they are so expensive. Depending on where you buy your shells from there is a small difference (about 0.0002"/0.0003") in the thickness and that affects the clearances you end up with - PM me for more details.

Some of the machining from the factory was not great - I've yet to measure a block/MBP with main bearing bore within spec!

Pete

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Re: Cross Drilled Crank

Post by rbgosling »

Cliffords wrote:
Tue May 17, 2022 07:15
Is the standard size of the mains and big end journals available anywhere ?

Many thanks

David
I'd have expected it to be in the Workshop Manual, which is usually pretty good about these things. But I don't have mine in front of me to check right now!

I would make certain the correct oversize bearing shells are available for the level of grind you want, before committing. For a normal block I think they should be, but I'd want to be certain, and preferably have them in my hand! I nearly messed up my rebuild because it turned out mine was one of a number of blocks that had the mains bearings honed over-size, requiring special thick bearing shells, which needless to say were totally unavailable.

Despite covering 175k miles, my journals were still within standard tolerance, so the machine shop just gave them a light polish rather than a grind.
"Farmer" Richard

1990 Lotus Excel SE (Lilith)
2022 MG MG5 EV (not due to be a classic for quite a few years...)

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Re: Cross Drilled Crank

Post by Alan_M »

Cliffords wrote:
Tue May 17, 2022 07:15

To my question is the standard size of the mains and big end journals available anywhere ?

Many thanks

David
Have you looked at the file I’ve put a link to in the engine section - I think it will have all the info you want in terms of what options there are. Then contact usual suppliers including Gary Kemp.

Cliffords
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Re: Cross Drilled Crank

Post by Cliffords »

Pete Boole wrote:
Tue May 17, 2022 12:09
Do you mean the bearing shells themselves? I believe they are lotus-specific - the reason they are so expensive. Depending on where you buy your shells from there is a small difference (about 0.0002"/0.0003") in the thickness and that affects the clearances you end up with - PM me for more details.

Some of the machining from the factory was not great - I've yet to measure a block/MBP with main bearing bore within spec!

Pete
Hi Pete
No we measured the actual journals on the crank . The reason I ask is ,if we regrind and they touch up and then take off 10 thou ,where you start with a 6-8 thou difference you get a right pickle when choosing oversize shells. Seems like we can get plus 10/20 or even 30 . What we found is the today size of each journals varies along the length of both the cranks we measured . If you then bolted it up and measured all the clearances with plus 10's in for example , some would be tight and some would be loose . My main problem is my son who measures this stuff and rebuilds the engines , works within the highest level of motorsport all day in pristine white rooms with high quality calibrated tools . He then sits in the garage here with a 40 year old block and explains to me the engine is made by blind men with tape measures and oil is full of rocks ! :D

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Re: Cross Drilled Crank

Post by Pete Boole »

Sorry - I thought you meant can you get generic shells for a different engine that would fit. Can't you just measure the bore of the conrod with new shells to come to the correct measurement for the crank grinder to use? That way you can also choose the clearance you want to run.

Just a thought!

Pete

Cliffords
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Re: Cross Drilled Crank

Post by Cliffords »

Pete Boole wrote:
Tue May 17, 2022 14:08
Sorry - I thought you meant can you get generic shells for a different engine that would fit. Can't you just measure the bore of the conrod with new shells to come to the correct measurement for the crank grinder to use? That way you can also choose the clearance you want to run.

Just a thought!

Pete
I think that's exactly what we will do , albeit it will differ across different journals so not just one oversize set of shells will do .
Or we grind all the journals to a consistent size . Unlike when it was made :D
Thanks
David

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