Line hone ?
 

So, I'm getting a clearance of .0012-.0014 on my 3' mains with the 113M speed-pro 3/4 groove bearings. I bought a new crank from Molnar which measures 2.9998 and thought that I could swap it out. So, I decided to measure the main bores without shells and I'm coming up with 3.1858. I know that the general rage is 3.1880-3.1890. So, does anyone know if this could be the culprit of these real tight numbers? if I got the bores honed to 3.1885, will it be enough to get back into range to say .003-.0036? From what I remember for every .001 of bore increase (with no bearings) you should see around a .0006 increase in bearing to crank clearance? Is this at all close to, right? Not sure if I should have the block line honed again.

If anyone could shed some light on this for me, I would really appreciate it,

Thanks

If I had that 3.1858" bore measurement I would definitely align-bore (maybe align-hone) the block. I think the clearances would then be real close to what you're looking for. Just my 2 cents.

Your new crank and main bores are within spec !

Pontiac set up there non RA / SD 3” main production motors for .0002” to .002” clearance, so your not far off from that .

If your main bore checks out dead on then I would not line hone it, but look for a bearing set to provide that extra .001” or so to get you to .003”.

If you can’t send back those bearings you have now and they have a break in coating ( which I have never found I need for) then I would wet sand it off from one bearing set with 800 grit paper and then drop them in one main saddle to see where your clearance move to.

Another possibility is if your line bore is only a hair out then just get a line hone job done with these bearings in the block.

This is in a way what Jenkins did with his SBC 400 motors when converting them over to run the smaller main 350 cid cranks.

Are you using a dial bore gauge to get your measurements? If yes, are you using a setting fixture or a micrometer to set the bore gauge? I guess what I am saying is verify your measuring tools are dead nuts on first. Have you changed the main bearing fasteners? Going from factory bolts to studs will close the housing bores up some. Also going from factory torque specs. to ARP specs will close them. Using ARP lube vs engine oil will close them as well. Bottom line, I want 70-75% of the housing bore diameter to be on the middle of the factory spec. +-.0002. The area around the parting line will be oversize.

I had 4 steel caps put on this motor 4 years ago. Since day 1 the clearances were tight to where I had to get the crank cut to fit. I've had some hard luck with the oiling over the last 3 years to where I had to change crankshafts twice. The first crank was a forged Ohio that was cross drilled. I had bad luck spun number 5 rod. Second crank was a ARMA steel crank which lasted longer but had bad luck with that as well. Never had a main bearing problem just rods. But both cranks needed to be cut on the mains to fit. Never could understand why they needed to be cut. My machinist had told me that he sized the mains to the middle of the range, so I just looked past that as being a problem. So, this time I decided to get a Molnar forged crank and when I had the same problem and being that I have 2 sets of main bearing I tried both and got the same .0012 numbers. So, I finally measured the bores and to my surprise they are small.

So now I'm going to have to get them honed, I guess. I hope that I'm not going to be charged for the line hone being that it wasn't done right in the first place, but you know how that goes ... it's been 4 years and a lot of money getting the 2 cranks cut lol..

So, I set the micrometer to 3.1880, then I zero out the bore gauge in the micrometer. From there I go to the torqued down main caps (without bearing shells) and measure. Came up with .0022 to the right of the zero. The mains all have ARP studs 4 torqued to 110 ft-lbs and 140 ft-lbs on rear, the studs were all installed at the time of fitting the caps.

Thank you for the details. Yes the ARP studs and their lube greatly increased the clamp load on the housing bores. That's as expected. A good machine shop can bring them right back into specs. without cutting the caps. It would take 8-10 strokes at #2 on the cutting pressure. Flipping the block a couple times. Should be easy work. I would definitely have it done. Like building a house, the line hone is the foundation for the entire build. Good luck with your build.

Thank you for your reply.

I'm using CMD Extreme pressure Lube #3 for the rod and main fasteners that Molnar recommends ..

Do you think by getting the bores to 3.1885 that it might bring the clearances to the .003 range? What would you like the see the clearances at?

The motor is a 8.3 to 1 twin turbo with iron heads, E85 for fuel. I'm going to try to keep the rpm's under 7000 if going all out, but mostly it will be 6000rpm's

Yes, that is your target dimension. That should bring your oil clearance in line. Now, I will get all crazy technical about the lube. Molnar and others love that extreme pressure #3 lube. Jesel, Eagle, Bill Miller all love it. Everyone but ARP! Even though ARP makes the fasteners for Molnar, Scat and the others. I like it too! But here is the deal. If you use Extreme pressure #3 on your ARP bolts, you need to stick with it. Don't use anything else after it's line honed. Now I understand why your housing bores have closed up more than normal. Extreme Pressure #3 provides even more clamping load than ARP Ultra Lube! Chances are if you cleaned off the #3 and used Ultra Lube the bores would be bigger. It's amazing how much these blocks move around with different torque and lube applied. I also recommend having your main studs float in the block. I do not bottom them out. I bottom them, back up 1/4 turn and mark the ends with a silver sharpie. That way when I tighten them I can make sure they stay in a marked position. This all makes sense now.

I went out and tried the ARP lube and it measured .0002 larger. So it did change a little..

WOW

GT

Since you’re going through this in great detail ( which is great and is what I would do too ) why not out of curiosity get fully crazy and bolt the heads on to see if the main bores move around .

I mean what would doing such take, a investment of another 3 hours of time if that?

What temperatures should these dimensions be checked at? And how much does it matter? I'm reading this and curious.

Rule of thumb is "room temperature", which I am guessing is 68-72F? My shop in the winter I keep between 52-55 F. Because I am cheap and that's a warm enough working temp for me. Crankshafts and cylinder bores typically measure .0001" smaller at that temp. Within the margin of error.

Thank you. When I built the SD455 I used dimensions from Pontiac shop manual. Shift about 5400rpm.

I did the same with my 73 SD engine with the exception of the rod bolts. I could not find or afford stock replacement SD rod bolts. I used ARP bolts and followed their stretch recommendations. My engine was done making any more power at around 5000 RPM''s Bone stock build.

Well I dont what to tell you however I have 16 Pontiac SD rod bolts still in packaging. Why when I found that SD block and rods I figured I needed new bolts. When Arnold Hines did the engine he said these original bolts will be fine. Soo. With the stock lift cam and blueprinted stock heads after trying different shift points 5400 seems ideal. In my street automatic car the upshift is 5400 from the factory.

Also the whole thing with insanely strong main fasteners has always left me scratching my head a bit.

Gray cast iron like our factory blocks are have a compressive and tensile strength of 18,000 and 90,000 psi respectively.

If we use a tensile strength average of 15,000 psi for a ok main stud and not even a top shelf real good one then that at a level that ok stud is near twice as strong as the cast iron where threading them into!
For a steel main cap it’s almost the same deal.

I think where at the overkill point with the strength of main stud steels here now.

Main stud preload is important as torque levels rise, to keep from unloading the cap-to-block joint.

If the joint stays together, then the fastener only experiences the steady preload.....no cyclic fatigue loads. So the fastener will live a long happy life if it's preloaded above operating loads. Cap fretting is a warning sign that the joint is unloading.

The overall strength of the threaded fastener looks at (3) factors:
a) tensile strength of fastener which is the thread stress area times the ultimate tensile strength of the material
b) thread stripping strength of the fastener which is governed by the fastener material, thread shear area and the length of thread engagement
c) thread stripping strength of the tapped hole which is governed by the same 3 factors. But the shear area of the thread in the block is larger than the shear area of the fastener since the effective diameter is bigger.

So the weaker block material can hold a stronger fastener material if the engagement length is sized correctly and the differences in thread shear area are understood.

Eric

This attention to every detail is why Mike's Pontiac engine in the Boss Bird made something north of 3000 hp and was all in one piece at the end of the 250 mph run.

Eric