Main Cap Walk
- Thread starter schulte
- Start date
My block has been done twice, not sure how much each time, but the cross bolts were not an issue
Tim your case doesn't sound too extreme. however if .003 were taken off the caps and .003 were taken off the block, that would require a .012" clearance hole, and that would be with the bolts touching the block. I don't know what the clearance actually is, but it adds up quick. im also wondering at what point will you will start to run into fitment issues with the thrust bearings.
You can drop the centerline of the main bore, but being gear drive camshaft I don't know how much that would affect gear lash. I would say take it to the machine shop and first see how much needs skimmed off.
You can also skim the block/cap mating surfaces, and re-line bore to the original centerline. This will just take material out of the cap to make it correct. It will also change how much the bearing sinks into the cap, and will protrude from the block slightly, but should NOT be an issue as long as the overall bearing crush is to spec.
Also we need to look at what caused the damage to the caps. For example, on a gas engine, you will see signs of caps walking if the engine was pushed into detonation a lot.
It baffles me to see this damage on a billet main cap with a girdle. Maybe the fact they don't have dowels is the issue. But then again, I'm no engineer
You can also skim the block/cap mating surfaces, and re-line bore to the original centerline. This will just take material out of the cap to make it correct. It will also change how much the bearing sinks into the cap, and will protrude from the block slightly, but should NOT be an issue as long as the overall bearing crush is to spec.
Also we need to look at what caused the damage to the caps. For example, on a gas engine, you will see signs of caps walking if the engine was pushed into detonation a lot.
It baffles me to see this damage on a billet main cap with a girdle. Maybe the fact they don't have dowels is the issue. But then again, I'm no engineer
You can drop the centerline of the main bore, but being gear drive camshaft I don't know how much that would affect gear lash. I would say take it to the machine shop and first see how much needs skimmed off.
You can also skim the block/cap mating surfaces, and re-line bore to the original centerline. This will just take material out of the cap to make it correct. It will also change how much the bearing sinks into the cap, and will protrude from the block slightly, but should NOT be an issue as long as the overall bearing crush is to spec.
Also we need to look at what caused the damage to the caps. For example, on a gas engine, you will see signs of caps walking if the engine was pushed into detonation a lot.
It baffles me to see this damage on a billet main cap with a girdle. Maybe the fact they don't have dowels is the issue. But then again, I'm no engineer
But since you work for Ariel, you know a heck of a lot more about designing to withstand immense forces than the average Joe...give yourself some credit :thumb:
It baffles me to see this damage on a billet main cap with a girdle. Maybe the fact they don't have dowels is the issue. But then again, I'm no engineer
it was said long ago that billet caps, main studs and a girdle would not stop crank walk.
This^. I'm no engine builder. But I'm a machinist by trade. A center line is a centerline.... If you shave the block and main cap mating surfaces, then you've made a slight oval, as long as your re bore your mains in the same center line as before, the crankshaft will be in the same spot. Piston protrusion, cam gear mesh, none of that will change.
That's what I originally thought.. That's true to the relation of cap and block. But it will still move it closer to the cam. You would have to do the .006, and .012 like I said to keep the relation to the cam the same. But at that point you'd have to over the cap bore to be a true circle again.
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I was under the impression that you would over bore the mains no matter what. I don't see any other way to make it right. So yes at that point nothing changes except bearing sizes (correct?).
Like I said Im no engine builder,(I'm sure there is a lot of tricks I don't know about!) but I make parts all day every day.:spit:
take a piece of paper and cut a circle of known diameter out of it and then cut it in half. imagine one side as the block and one side as the main cap. trim some from both sides of the "mating" surfaces, put the pieces together and measure the diameters both ways. It will shrink both parallel to the cut as well as normal to the cut. as long as you don't take any material out of the mains in the block, your centerline remains the same. of course in order to do this, you need to take more out of the cap. you can see this by placing the paper circle back over the hole previously cut.
When you align hone a block centerline is taken into account. It must be verified to along with decking/truing the block so that centerline for each side us the same. The block can be fixed by using the method of the previous poster. When using the girdle you would take into account how much was removed from the caps to determine if additional machine work was required on the rail of the block. A fee thousandths shouldn't require any additional work. The girdle should flex that much. In a perfect world you would want it dead nuts on with no deviations. Main point is though you can salvage your block. Secondly determine what caused it. I believe it most likely came from no alignment dowels on the caps. Personally I would remedy that while I was at it. At least speak to the supplier of the main caps and get his opinion as to why.
Yeah I have no doubt it can be done with an oversize bearing to bring it back. I posted again rethinking my thoughts after someone mentioned there may not be oversize bearings available. If there are, yes.
I guess I wasn't around back then! I never realized the billet mains for the dmax didn't have dowels!?!
Oh no, if something breaks we just make it bigger :angel:
pretty sure you were here when Jeff posted about them a year or two ago. there were a few others that said the same but then everyone said "then why would socal diesel and many other reputable shops sell them and say to run them in big hp motors". i would bet that it all helps, it just cant be elimiated unless a new block is designed. id be interested to see how a high hp LML block does here with billet hold downs, studs, and a girdle. IIRC the internal webbing was increased and strength was upped 5-10% over older blocks