Machining Your Own Main Caps

[CTX-SLPR]

So Guys, no one responded to my thread on bringing back that well worn Buick Stage II V6 block so I'm still scratching my head on it.

One of the big things that is missing is the front and rear main caps. On a Stage II of that vintage the front and rear main caps were basically production units. Billet replacements are available (and pricey, especially for the main cap). I know they are precision machined pieces but what really is the holdup from making one yourself? I could machine it to something like +0.010in then have a precision shop finalize it to the right main bearing diameter and cap to web interface while leaving it wide enough for the engine shop to fit to the register. Doesn't seem like it would be that hard, what am I missing?

Thanks

[Matt Cramer]

As long as the material grade is strong enough, I don't see any problem with it. Might be best to line-bore the whole thing once you put the homemade caps on there.

[Loren]

I don't think you're missing anything...try it, then you can tell us what happened.

I am guessing that most shops with the ability and willingness to work with you won't mind you bringing your own material along but the more cutting you do yourself first the more you're just going to annoy them...the biggest challenge here will not be technical, but a matter of costs, practicality, cooperation. (Normal post-college lessons for young engineers.)

Probably the closest anybody is going to get them, which should be pretty close, you'd still want to finish with the usual align bore process anyway. At that point, if you can machine at all (i.e. you have access to a good knee mill, flycutter and some measuring tools) why not just improve your own machining enough to cover the job, or another alternative would be to find stock caps that are close enough they could have the mating surfaces cut and be align-bored in with the rest of the existing ones?

[hauen]

I wonder if you could use 4.0/4.6 Rover main caps?

[ImpalaSam]

If you have the means to manufacture them, there is really nothing special. Just match the bolt spacing
and the register width, then leave the bore roughly .030 under for the shop to align bore. If you have a
milling machine, should be no problem.

[BBR]

What am I missing? If they are basically production units, why reinvent the wheel?

[CTX-SLPR]

What am I missing? If they are basically production units, why reinvent the wheel?

I'm concern about not having them fit the registers in the block honestly. I don't know if its bah and humbug but the general wisdom seems to be that caps from a different block are a lucky chance to fit properly in the registers. I'd definately need a line hone/bore to make anything work so I'm largely discounting that as a driver in this situation.

I have a mill, though I seem to spend more time burning up endmills trying to mill stuff vs. using it as a really good drill press. I'm learning how to set things up properly and for Aluminum I'm doing good with setting my speeds and feeds. Steel is kicking my butt even with looking stuff up!

[Loren]

If you're having trouble starting out, a couple shop tips particular to steel (all of which can be argued about among machinists but will get you on the right track):

Assuming you're using regular ol' cold-roll bar from the steel supply and nothing exotic, and knowing that you will be machining at a small fraction of the speed of aluminum; 1. Use two-flute end mills so there is only one flute "in-the-cut" at one time (the machine will have an easier time), 2. Use HSS not carbide cutters because carbide works well in a precise machine under precise conditions but not in your garage, and get mid-priced cutters -not the cheapest/not the best-, 3. If you're cutting straight into the material only go a half-inch at a time or less for depth and if you're shaving off the side of a one-inch block or so only go 1/4 the cutter diameter at a time, 4. Flood the cutter w/ a mix of one-eighth soluble oil and water from a squirt bottle such as they sell for WD-40, you want to keep the cutter cool enough at each squirt so that it doesn't steam on the next one, 5. Go with whatever (slow) speed recommendation but after that, table travel is based on chip thickness i.e. the amount of distance advanced for each pass of a cutter flute...you for sure shouldn't go too much but also avoid going too little and 6. Have the ways that you're not using (i.e. Z and Y axis if you're cutting along X) locked down to minimize the table being able to rattle around. 7. Obviously you generally make rough cuts to get close and then for example an .020, an .005 then an .002 or 1 to get to final dimension, the cutter and machine will always deflect under force and you want the last cuts to be very light to minimize that. 8. Have the cutter rotating into/against the feed direction unless you're only shaving a couple thousanths.

I don't know where you're on this but usually when someone is having trouble he's missing on one or more of the above general things.

[CTX-SLPR]

If you're having trouble starting out, a couple shop tips particular to steel (all of which can be argued about among machinists but will get you on the right track):

1. Use two-flute end mills so there is only one flute "in-the-cut" at one time (the machine will have an easier time),
2. Use HSS not carbide cutters because carbide works well in a precise machine under precise conditions but not in your garage, and get mid-priced cutters -not the cheapest/not the best-,
3. If you're cutting straight into the material only go a half-inch at a time or less for depth and if you're shaving off the side of a one-inch block or so only go 1/4 the cutter diameter at a time,
4. Flood the cutter w/ a mix of one-eighth soluble oil and water from a squirt bottle such as they sell for WD-40, you want to keep the cutter cool enough at each squirt so that it doesn't steam on the next one,
5. Go with whatever (slow) speed recommendation but after that, table travel is based on chip thickness i.e. the amount of distance advanced for each pass of a cutter flute...you for sure shouldn't go too much but also avoid going too little and
6. Have the ways that you're not using (i.e. Z and Y axis if you're cutting along X) locked down to minimize the table being able to rattle around.
7. Obviously you generally make rough cuts to get close and then for example an .020, an .005 then an .002 or 1 to get to final dimension, the cutter and machine will always deflect under force and you want the last cuts to be very light to minimize that.
8. Have the cutter rotating into/against the feed direction unless you're only shaving a couple thousanths.

I don't know where you're on this but usually when someone is having trouble he's missing on one or more of the above general things.

I pulled the speeds and feeds from a website calculator that I guess I trusted because it looked to have lots of parameters (and defaults for the more esoteric that I didn't know). I was cutting the unknown steel of my brake pedal and I was just burning up the cutters.
I think I messed up #4 for sure and probably #8, I did burn up both 2 and 4 flute cutters though I was inputting the number of flutes into the calculator. I have some Shars TiN coated imports that were sorta middle of the catalog but probably on the cheaper end. Since most of the 3/8in+ cutters are shot I either need to replace or get them resharpened and recoated.

Thought?

[ImpalaSam]

When machining on unknown materials such as your brake pedal, before attempting a cut try and file the material,
it should "bite" into the material easily, if it doesn't the material could be hardened, if that is the case you will
go through a lot of cutters and maybe carbide will be your only hope. Do some research on "Climb" and
"Conventional" milling, very important concept when milling.

[383gta]

Time vs money. Unless you have made caps from scratch before it will take forever and after buying the right material won't save much money over the aftermarket caps.No matter what you do the block will need align bored. Fitting stock caps from another block is not a big deal and will save you many many hours and $$$. You will still get to play on your mill because replacement caps from another block will need to be properly fitted. They will be shifted to one side. You will need to measure how far it is shifted by snapping it into the register. Then mill the appropriate amount off one side and weld the other and mill it back to the right width. I prefer to tig weld the one side. I use a mill vise squared to the table with the cap upside down in the vise after you are happy with the fit put it back in the vise and cut .030 off the parting edge and take it to a machine shop for align boring. One other thing. Make sure you level the cap before you cut in the mill. I have gotten blocks that people have done themselves and either they didn't square their vise or level the cap when they cut it. I cringe every time I hear a customer say they fit the caps themselves even other machine shops can't seem to get it right. 90% of the time I have to fix something.

[anotheridiot]

machine shops prefer to have cad drawings not to just throw into the NC. Spend your time on auto cad and they will probably do all the work for the same price since you getting it to +/-.010 is just way too close for them to not spend endless time on setup. I dont think anyone would mind you taking a hunk of 7075 aluminum to them though.

[Scott Liggett]

Four bolt main caps are available aftermarket. We convert 30 350 blocks per day and buy the main caps by the pallet.

[CTX-SLPR]

It's a Buick V6. While they do have billet caps available, they are expensive.

At this point I'm really unsure of what to do since it's not close by to just grab, I'd have to have it shipped from OH to CA. I think I could get it functional locally with getting the cylinders sleeved and then start trial fitting main caps either from my spare engine that I already have or just hitting up the Turbo6 community for spares laying around.

[V12guy]

Years ago when I worked for a Super Stock racer he had me make up 5 or 6 sets of Steel ,Main caps for a 427 Ford. The ones I made allowed a standard 427 to become a "Cross Bolt" block, so I DO understand that some things are not "off the shelf".
We mated the surfaces up (Top, Bottom, Sides) and then align bored the whole thing.