Ford BD cranks.

[mickrick]

I'm doing a bit of planning to build a BGD for my Caterham, and I just wanted confirmation on the difference between the wide journal, and narrow journal cranks?
Is the narrow journal to allow radius in the big end journals for a stronger crank?
And what are the 6 and 12 bolt referring to?

I just managed to find a copy of David Visard book on these engines. It's still in the post...
Are there any other publications that anyone can recommend for these engines?

Cheers, M.

[99hjhm]

6/12 bolt is the number of fasteners holding the flywheel onto the back of the crankshaft.

[Mignon]

The standard Ford Kent crank has 26.7 mm wide big end journals with 22.2 mm wide bearings. The narrow journal cranks are 23.7 mm with 19 mm wide bearings. The change was probably just to reduce bearing friction. I think the narrow journal cranks were first introduced in the Lotus Twin Cam but I'm not sure of the history.

6 or 12 bolt is obviously the number of flywheel bolt holes.

If only you could have found some way to get connected to the internet you could have Googled all this in a couple of minutes.

[mickrick]

Thank you for the response Gentlemen.
Better to ask on here than wade through all the links trying to sell me st I think
I would have thought a wider bearing area would have been better though

[mickrick]

OK. Found a definitive answer for the narrow journal question.
https://help.summitracing.com/app/answers/detail/a...

[PaulKemp]

Every day’s a school day
Thanks for that

[Mignon]

mickrick said:

OK. Found a definitive answer for the narrow journal question.
https://help.summitracing.com/app/answers/detail/a...

Except this is not the right answer and you have completely misunderstood it. This is an explanation of why a "bearing" might need to be narrower on a journal of a given width. On the Ford Kent it is the journal that is narrower not just the bearing and as my first post made clear, both the journal and the bearing are about 3 mm narrower on the narrow crank which tells you the fillet radius must be about the same on both.

[mickrick]

Thanks for your replies.
So you're saying the journal is narrower to reduce friction?

[mickrick]

Thank you Mr. Mignon. Mrs. Wilcox also confirmed your comments
The Vizard book turned out to be more about the Lotus twinks than BD's, there is a bit about BDA's in the back, but it's all very basic tuning stuff.
I also have a book of photocopied Cosworth sheets, but again, it's all a bit outdated, and I've already found a couple of misprints, so even Cosworth make mistakes.
So I have another question.
If Farndon, and other builders can supply a top notch steel crank for around 1300 quid mark, how can Arrow justify 2.5k?

[Mignon]

I guess they work on the basis that if they charge enough a few people will think it must be a better product so they make a small number of very large profits rather than a bigger number of smaller ones.

[227bhp]

Maybe they're more accurate than Farndon and don't take 6 months + to make a crank.

[mickrick]

227bhp said:

Maybe they're more accurate than Farndon and don't take 6 months + to make a crank.

Sounds like you have had previous experience with Farndon? Have you had a crank out of tolerance from them then?
Wilcox charge around the same for theirs. I have no idea who supplies their cranks, but they wouldn't sell rubbish that's for sure.

[99hjhm]

I’m not going to get into a slagging off Farndon as still use them, why, because they are cheap. BUT... you get what you pay for.

Arrow crankshafts come with documentation, certification and reports. Farndon nothing. They have now gone over to full CAD/CAM to improve lead times which are probably just as long as Farndon.

[mickrick]

You recon the Arrow crank is worth the extra dough then? The rods look nice too.

[99hjhm]

Yes I could recommend Arrow products. Actually I’ll go as far as saying never had a single issue with any Arrow product and used a fair few. BD engines are not cheap so if building one I would Be fitting arrow.