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Steel Main cap material

General engine tech -- Drag Racing to Circle Track

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Exminiman
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Re: Steel Main cap material

Post by Exminiman »

Kevin Johnson wrote: Sun Jul 05, 2020 2:42 am
Exminiman wrote: Sun Jul 05, 2020 2:04 am ...
Stock centre cap is suffering from some porosity, which I am concerned will start a stress crack
The crank is Forged EN40B steel which is quite stiff, I am concerned it will aggravate any shortcomings on main caps...
Maybe I am over thinking it.....
...
I do not think that you are over thinking it. You have identified a weak link. Trust your judgment.

For those who do not know, this is a three-main bearing crank.

~~~~~~~~~~~~~~~~~~

Any pics of the new crank? Does it use dummy mains? Just curious as I made many parts for these engines.
This is actually a factory crank.....here are a few stock photos, saves me going out to workshop..
49C88A32-740B-46FB-AC97-CA8CB36DCD26.jpeg
C605C551-6135-494C-90C5-188283E57D31.jpeg
07558230-1148-4D10-AA9D-D36FBBD35218.jpeg
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Kevin Johnson
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Re: Steel Main cap material

Post by Kevin Johnson »

Sorry about going into the bushes with aluminium. Too many engines and too sleepy. #-o #-o :oops: :lol:
ClassicComp
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Re: Steel Main cap material

Post by ClassicComp »

1018 hrs.
If you need them made pm me
results speak for themselves
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Re: Steel Main cap material

Post by BCjohnny »

Almost any HRS structural grade will do, ask a local flame cutting shop for offcuts, they go in the scrap usually

If you're jobbing all the machine work out the actual cost of the steel is infinitesimal compared to all the other costs, so EN8 might make you fell better

If they're made accurately enough leave ~ 15-20 thou on the radius for align boring

Throw some 12.9 capscrews at it also
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Exminiman
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Re: Steel Main cap material

Post by Exminiman »

BCjohnny wrote: Sun Jul 05, 2020 9:03 am Almost any HRS structural grade will do, ask a local flame cutting shop for offcuts, they go in the scrap usually

If you're jobbing all the machine work out the actual cost of the steel is infinitesimal compared to all the other costs, so EN8 might make you fell better

If they're made accurately enough leave ~ 15-20 thou on the radius for align boring

Throw some 12.9 capscrews at it also
Thanks for this, its really useful, I was wondering about how much meat to leave for the inline boring, have a set of ARP studs (converting from bolts) but will need a couple more as will do as 4 bolt/stud.

I have seen the two extra studs/bolts inclined at about 10 degrees, is this worth it ? - top wack of the motor will be about 120BHP....
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Re: Steel Main cap material

Post by 4sfed »

Unless you plan to make them yourself, you can buy a set from Mini Mania.
Screenshot_20200706-090026.png
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Exminiman
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Re: Steel Main cap material

Post by Exminiman »

4sfed wrote: Mon Jul 06, 2020 9:06 am Unless you plan to make them yourself, you can buy a set from Mini Mania.
Screenshot_20200706-090026.png
Thanks, I did try them, my block is an early Thin flange block, which has slightly different bolt spacing on main caps, they sent me what they thought were right, but unfortunately not.
So, I am in process of making some.......
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Re: Steel Main cap material

Post by BCjohnny »

I have seen the two extra studs/bolts inclined at about 10 degrees, is this worth it ? - top wack of the motor will be about 120BHP....
For the amount of work you're investing anyway it's not going to hurt anything ..... although I doubt it's absolutely necessary

Good luck with it all
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Kevin Johnson
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Re: Steel Main cap material

Post by Kevin Johnson »

BCjohnny wrote: Tue Jul 07, 2020 4:01 am
I have seen the two extra studs/bolts inclined at about 10 degrees, is this worth it ? - top wack of the motor will be about 120BHP....
For the amount of work you're investing anyway it's not going to hurt anything ..... although I doubt it's absolutely necessary

Good luck with it all
Try to have a young interested lad or lassie there to learn some of this.
Exminiman
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Re: Steel Main cap material

Post by Exminiman »

Thanks a lot for advice guys, not being a professional engine builder, just an enthusiastic amateur, I was a little hesitant with my first post, for no good reason, thanks again for making me feel welcome. :D
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Re: Steel Main cap material

Post by MadBill »

Exminiman wrote: Sun Jul 05, 2020 2:04 am...
The crank is Forged EN40B steel which is quite stiff, I am concerned it will aggravate any shortcomings on main caps...
Maybe I am over thinking it.....
Just for general knowledge, all steels regardless of tensile strength have virtually the same stiffness (Young's Modulus)
Felix, qui potuit rerum cognscere causas.

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Exminiman
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Re: Steel Main cap material

Post by Exminiman »

Exminiman wrote: Mon Jul 06, 2020 7:07 pm
4sfed wrote: Mon Jul 06, 2020 9:06 am Unless you plan to make them yourself, you can buy a set from Mini Mania.
Screenshot_20200706-090026.png
Thanks, I did try them, my block is an early Thin flange block, which has slightly different dowel size, they sent me what they thought were right, but unfortunately not.
So, I am in process of making some.......
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Re: Steel Main cap material

Post by MadBill »

Making caps or making stepped dowels?
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Re: Steel Main cap material

Post by Krooser »

I applaud your efforts. Not many amateurs would attempt this on their own.

The little BMC engines have a spot in my heart. My older brother had a Morris Minor circa 1960 and he left me tools and instructions on how to dissemble the engine in preparation for a sorely needed valve regrind. At age 11 it was a fun project... hauling the head to the machine shop in my little red wagon and getting it reassembled before he came home from his out of town door to door vacuum cleaner sales job!

He ice raced the little Minor for a few years and beat a fair share of Vettes and other higher hp machines due to the obvious lack of HP that would not allow much wheel spin!

A winning crew chief at age 11... Have to put that on my resume.
Honored to be a member of the Luxemburg Speedway Hall of Fame Class of 2019
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