Billet Main ?

we4Mateo

Double you eee what?
I scored a set of billet main caps, just the two centers, for my new 109 but they are machined for a girdle and I am not going to use a girdle. I'll be using studs and a steel crank. My question is: any strength lost from being machined flat for the girdle? I would think they would clamp the same, but if there is strength lost from the meat taken out, then I'll get new ones. TIA.
 
My first impression is to say they will be stronger than a stock cap, but not as strong as an unmachined billet cap.
 
The strength is really in the material. It is a meatier piece altogether. I dont know how much is machined off, but I would have to measure. I have unmachined caps to check. Worse case scenario would be to have your machinist make a piece to replace what would be missing. The cap would not know if it were a piece or the girdle. The crank is not going to stretch/move the cap any different. If your not using a girdle, i would add the other caps. always build as strong as you can.

:D
 
The strength is really in the material. It is a meatier piece altogether. I dont know how much is machined off, but I would have to measure. I have unmachined caps to check. Worse case scenario would be to have your machinist make a piece to replace what would be missing. The cap would not know if it were a piece or the girdle. The crank is not going to stretch/move the cap any different. If your not using a girdle, i would add the other caps. always build as strong as you can.

:D

Agreed. I was only planning on replacing the two center caps though. I figure with a good crank, there shouldn't be as much flexing around in the first place and even with a stock crank, I haven't seen #1 or #4 main caps fail yet. I don't think there's enough leverage on the ends. I'm far from an expert but I have been asking a lot of people who have already blown these things up. I don't see how the caps I have could be less strong simply from being machined flat on the bottom, but I don't want to open this thing up again except for bearings. Anyone else ever used girdle machined main caps without a girdle?
 
And your very unlikely to see a damaged #1 or #4 main bearing ever cause you grief unless you screw yourself in the balancing department.
Likewise, #2 & #3 mains get mucho blameo for troubles, that is where the block is weakest along the main axis and under stress (boost) the block is twisted by the bellhousing opposite of crankshaft rotation yet held by pan rail located motor mounts, causing a mis-alignment of the main bearing centerline.
For what it's worth...the factory cast/rolled fillet nodular iron crankshaft is actually torsionally "Stiffer" than StgII/aftermarket forged steel crankshafts, an arguement for another day just as long as you bring your math to class for the whys/wheres, and yes..oil pressure is involved.

Kevin.
 
If memory serves me correctly, the amount cut off is between .375" - .500". It's been a few years since I compared them. Even at a .250" it would be a good percentage of strength. For peace of mind, you might consider buying new.
 
Thanks for all the info guys. Keep it coming. I'm looking for reliable and fast but I know it'll take some $ so I'm willing to take the time to do it right. I don't want a girdle though and I believe 600rwhp is doable without one. Any and all suggestions welcome.
 
Well being a tooling engineer, I would either add the piece of steel back on top, or post in the parts wanted and trade someone who is going to use girdle cut caps.
Im looking at 3 billet caps right now. Measure how tall they are from the surface that sits in the block, and I will tell you how much was taken off. I have a front and 2 centers to look at.
 
Well being a tooling engineer, I would either add the piece of steel back on top, or post in the parts wanted and trade someone who is going to use girdle cut caps.
Im looking at 3 billet caps right now. Measure how tall they are from the surface that sits in the block, and I will tell you how much was taken off. I have a front and 2 centers to look at.

I appreciate the offer. I'm just going to try and trade them for a new set. Someone who wants a girdle will save on the machining then.
 
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