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Best compromise for less than ideal main bearing bolt design?

I appreciate everyone's input and the varying aspects of this you've brought to mind. I wanted to provide some dimensions on the fasteners and how they're currently threading into the block so as to clear up any confusion *EDIT* Drawing removed as it had some errors.

I don't have a thread mic or wires on hand so take my minor diameter measurements with some salt as I had to eyeball the caliper jaws. Interestingly the only difference between the inner and outer studs is the length of the coarse threaded portion that threads into the block--once threaded in the studs are proud of the holes by the same amount. Also the thread anti-seize the kit manufacturer supplies gives a general K factor of .16.

For comparison sake I took a look at the original bolts for the stock bearing caps, they are reduced shank (shank same diameter as minor) M12 grade 10.9, and because of the stepped nature of the stock bearing cap, the inner bolt is prouder of the hole than outer bolt (but the tightening torque is the same).

After doing a bunch of reading I think the best thing we could do with what we have is machine the shank of the studs down to the minor diameter of the coarse threads and machine some of the coarse threads off so the stud engages lower in the block. This would result in a more uniform tension over the stud's length, a better fatigue resistance to cyclical loading, less stress on the block threads, and cutting back the threads would mimic the effect of the original counterbore. To set stud tension we'd calculate the stretch required to achieve desired preload (85-90%) and set up a DI to measure during the torque sequence.

Unfortunately given that we don't own a lathe and there's ten hardened studs, I don't think it'd be economically practical to do this.
 

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I appreciate everyone's input and the varying aspects of this you've brought to mind. I wanted to provide some dimensions on the fasteners and how they're currently threading into the block so as to clear up any confusion.
View attachment 426706
I don't have a thread mic or wires on hand so take my minor diameter measurements with some salt as I had to eyeball the caliper jaws. Interestingly the only difference between the inner and outer studs is the length of the coarse threaded portion that threads into the block--once threaded in the studs are proud of the holes by the same amount. Also the thread anti-seize the kit manufacturer supplies gives a general K factor of .16.

For comparison sake I took a look at the original bolts for the stock bearing caps, they are reduced shank (shank same diameter as minor) M12 grade 10.9, and because of the stepped nature of the stock bearing cap, the inner bolt is prouder of the hole than outer bolt (but the tightening torque is the same).

After doing a bunch of reading I think the best thing we could do with what we have is machine the shank of the studs down to the minor diameter of the coarse threads and machine some of the coarse threads off so the stud engages lower in the block. This would result in a more uniform tension over the stud's length, a better fatigue resistance to cyclical loading, less stress on the block threads, and cutting back the threads would mimic the effect of the original counterbore. To set stud tension we'd calculate the stretch required to achieve desired preload (85-90%) and set up a DI to measure during the torque sequence.

Unfortunately given that we don't own a lathe and there's ten hardened studs, I don't think it'd be economically practical to do this.
Very good plan. If you are modifying the engine to increase output, look at moving peak torque to a higher rpm. Even if a different camshaft or what ever. Maybe propane injection, increasing spray pressure, etc.
 
You're saying you can't change the fastener- in several posts

and you can't change the threads in the clamped material- again, in several posts

What are you leaving people to suggest, as you've eliminated all possibilities?

Voodoo?
 
Inquiring minds want to know: what's the purpose of this project? What is the expected life of this engine?
I see some strange stuff here.
 
If the studs are truly 'hard' then a lathe is not gonna do you much good. But I've machined ARP hardware before and those bolts were not that hard.

Either way, I'd find a guy with a grinder who can remove the material the way it should be done - precisely and with coolant, leaving a fine finish. As I said earlier, ARP will still not love you for doing it.

But you still haven't addressed how the block is gonna like 200lbs of torque when it was born unto this world with 95lbs in mind.
 
We discussed the matter with an engineer at ARP who said the best way to deal with this is to turn down the shank and the unwanted threads to the minor diameter of the coarse threads on a lathe, use a .4" fillet radius where the top of the stud transitions to this diameter (after the fine threads). We need to make sure the bolt doesn't get hot and that it ends up with a good surface finish after (probably chuck it up in a drill use sand paper). This way we get an even tension through the bolt with no notch effects (vs grinding unwanted threads off) and we tension the block in a place where it can better handle it without removing more material from the hole.

Going to take this to a few machinists and see if it can be done in one or two billable hours (the most we could afford).

With regards to some of the questions: the engine is being built, as best it can, to reliably tolerate higher than factory cylinder pressures and have a wide powerband. Putting the power higher in the RPM isn't not optimal given the engine utilizes a HEUI injection system which is relatively slow such that 3k is the limit; the powerband will narrow quite a bit if this is done since there's no headroom. The bedplate has the effect of distributing the load better across all mains fasteners and also ties in to the rails to increase rigidity of the crankcase as a whole and further distribute load.
 
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Going to take this to a few machinists and see if it can be done in one or two billable hours (the most we could afford).

Stop right there, your killing me :ROFLMAO: :ROFLMAO: :ROFLMAO: :ROFLMAO: :ROFLMAO: o_O 😂

The sad part is your going to waste an inordinate amount of the shop owners time explaining the finer points of your "project" before you tell him you can only afford 1-2 billable hours.

btw shop rates aren't $40-60/hour anymore. I've lost count the number of times some amateurs come to the door and watched their jaws drop when I mention shop rate. I get that out the way as quickly as possible to weed out the cheap arses and dreamers.

Fuck, thank you for the joke, that made my day.
 
Thanks for your contribution!

We've gotten a few quotes already from some smaller shops with a few more on the way that are saying two to three billable hours (which we can afford at the quoted rates). This isn't our first rodeo. The concept is pretty quickly articulated when we show them the drawing we drafted for the work to be done (not the same as the napkin drawing cranked out up thread). Some of the larger shops we've spoken with are able to accommodate small odd jobs* but this one has a couple too many quirks... we've had some good laughs over the business realities of the average metro area machine shop these days.

Am exchanging some emails with the ARP engineer to get more input on certain design tolerances that could potentially make the job more economical. Whatever it ends up being I'll follow up with this thread as reference for future passerby's.

In the end someone will be paid what they ask to do this work. They'll get a little extra cash to keep the lights on or whatever and we will get the proper bolts. My apologies if this whole free exchange of work for currency thing is upsetting to you.

*Aside from helping to take in a couple bucks when it's slow, in my experience they say they do this to support the local community in a way... they're just as bummed at the decline of the "small job shop" as everyone else.
 
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The real answer to all your questions is....no one knows.

There are too many variables. Odd ball stuff like this is usually solved by trial and error.

Like most racing applications, you need to blow up several engines to get your answers.

Speed/torque/horsepower/longevity cost money. How deep is your wallet???????
 
Speed/torque/horsepower/longevity cost money. How deep is your wallet???????
Well, we wouldn't be bothering with the particulars of this bolted joint if a lot of money wasn't already invested in this thing.

To be clear the main question of this thread was: what is the best way to improve this sub-par bolted joint given the constraints? Thanks to some research and contributions from members here, an answer that's as informed as it can be has been arrived at. Just a matter of fine tuning some specifics and having the work done.
 
Thanks for your contribution!

Pleasure as always

In the end someone will be paid what they ask to do this work. They'll get a little extra cash to keep the lights on or whatever and we will get the proper bolts. My apologies if this whole free exchange of work for currency thing is upsetting to you.

*Aside from helping to take in a couple bucks when it's slow, in my experience they say they do this to support the local community in a way... they're just as bummed at the decline of the "small job shop" as everyone else.

I have found supporting the local community has generally been at my expense.

I'm tired of the
"it should only take xx hours"
or
"I though the shop rate was $50/hour"
Not saying that's you, but there's plenty out there.

I'm quite familiar with the concept of getting work in an effort to keep the lights on, more so then you.
Don't need you to remind me, this is the reality of being a very small business.

If I have to take on work to keep the lights on I will. At least I want to retain my dignity, not feel like I've had my prostate checked with a fist. (some people like that, not me)

------------------------------------------

Automotive and cycle guys are the worst to deal with. Seem to always want something for nothing, or very little.
"Can you help me with my project" sets of alarm bells here. Nope not anymore.
 
I work on some gun parts for a friend, very wealthy retiree.

always says "i'll pay you" but never does.

To add insult to injury. I did some parts, didn't get paid, and I picked up the lunch tab, because he's notoriously slow putting his hand in his pocket.

Last job I told him would be $xxx, still haven't seen any money.

This why I'm a grumpy old (well hung and good looking) bastard.
 
I can understand the cynicism and I've heard it from some of the folks we've spoken to (like you said cyclists seem to be a sore spot). I just want to be clear that we are coming to our local shops with a non-rush job that is very clearly defined looking for a quote. If we can get some of the particulars on the more generous side of tolerance and figure out the best way to fixture then it can work out economically for both us and the shop, and we will pay for the work.

That's the way I like it because it means they will be there the next time I have some odd thing that needs taking care of (until I can get my own small job operation up and running anyway).
 
I can understand the cynicism and I've heard it from some of the folks we've spoken to (like you said cyclists seem to be a sore spot). I just want to be clear that we are coming to our local shops with a non-rush job that is very clearly defined looking for a quote. If we can get some of the particulars on the more generous side of tolerance and figure out the best way to fixture then it can work out economically for both us and the shop, and we will pay for the work.

That's the way I like it because it means they will be there the next time I have some odd thing that needs taking care of (until I can get my own small job operation up and running anyway).

I hope it works out for you.

Agreed always good to have working relation with shops willing to do small qty/one-offs/proto/r&d work.
 
To be honest, not sure what I'm crying about. All the guys I do the side work for are great company, and good friends. Even though their a bunch of free loading bastards. Really not that big a deal.
 
I have heard of making the female thread at a slightly coarser thread pitch to compensate for bolt stretch and keep engagement low in the block. I have never done it and the engineering is nontrivial.
 








 
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