This has been an interesting couple of pages. Turns out it really wasnt an easy question to answer.
Main Cap Walk
- Thread starter schulte
- Start date
You are over thinking it.
First, match machine the flats. The cap is now closer to the cam by whatever amount.
Now line bore the mains to the original diameter using the center of the block half circle as the center. You do this with the caps installed and torqued. This will remove material from the cap only.
Mains are now centered on the original line and are the original diameter. Block side is every so slightly less than a half circle, a little more than a half on the cap.
First, match machine the flats. The cap is now closer to the cam by whatever amount.
Now line bore the mains to the original diameter using the center of the block half circle as the center. You do this with the caps installed and torqued. This will remove material from the cap only.
Mains are now centered on the original line and are the original diameter. Block side is every so slightly less than a half circle, a little more than a half on the cap.
It's not Tom. It's really simple. Folks are over thinking this. I can't explain things as eloquently as fingers can.
To me its fairly cut and dry. If the block is tore up any fix you have to fudge a little at the mating area of main bore.
I get what fingers is saying it may be minor fudging by a damn good machinist.
But in a 1000rwhp build and an engine known for crank flex, how much fudging is too much.
Now if this was a stock rebuild I would be all about it, and have no reservations, but from what the op is stating he is planning on putting the power right back to this thing.
I guess I still don't see how you can get the same centerline without coming out with a less than perfect circle, or moving the centerline up?? Can someone draw another pic? Or I can tomorrow on a cad after work
That is exactly what I was doing but I am not allowed to post pics here anymore. I am sure once you post up the pic it will make the discussion much easier.
Well dang since you said that I can't either lol I forgot? Said the tapatalk needs to be updated, but it is updated. I can try and figure out how on my laptop
Basically it will take a little off the main and the cap where the two parts meet, but depending on how much you removed from the two mating surfaces it will take more off the cap at the bottom to in the end make a circle.
If you draw a circle and put marks at 0,90,180,270, and put that circle on the main with 0 at the top of the block main and 90 and 270 at the shoulders where the cap meets the block, 180 at the bottom or middle of the cap, then at 90 and 270 you would take a little off the cap but at 180, this is where the most material would be removed to reflect how much you took off the shoulders.
Yes I knew. Since its like a tangent it will only get smaller so you don't need a "overbore" the 90 and 270 will barely be hit to be prefect circle again. That will still be good. But same with the 180, it doesn't matter how much material is left the only thing that matters is 0. And that's where your gonna take material off and cause cam-crank cl to cl to change.
Cam to crank cl Is determined by the 90 and 270 location on the block, regardless of bore size. The centerline will follow the block 90 and 270 since they are always stationary. If they where "movable" like the cap 90 and 270 it wouldn't effect it; but its not.
Again I'm not engine builder but I just can't see how in the world it would be any different.
Unless you have a way to bore it where it kinda doesn't self center and it just mills off the bottom cap. But that would give you and oval in loose terminology.
Cam to crank cl Is determined by the 90 and 270 location on the block, regardless of bore size. The centerline will follow the block 90 and 270 since they are always stationary. If they where "movable" like the cap 90 and 270 it wouldn't effect it; but its not.
Again I'm not engine builder but I just can't see how in the world it would be any different.
Unless you have a way to bore it where it kinda doesn't self center and it just mills off the bottom cap. But that would give you and oval in loose terminology.
I would think you zero your tool out at 0 or centerline using the main as top or 0 degrees and the 90 and 270. Then the only place you take material off is in the cap. This would be in a fixed jig so to speak so your tool can't walk around. You would start taking material off at the 180 mark and keep going till it contacts the 0 mark making a perfect circle.
It's all good. I remember this from when I was 16 and watching a machinist at the CAT dealer I worked at align bore different stuff including a 3512 engine block for ironically the same thing.
I doubt the movement had anything to do with with the girdle and main bearing cap as they are far stronger materials than the actual engine block, locating centers are important and I would've machined a dowel pin into the main cap+block.
No one knows what kind of fastener tension it had holding down the cap, this is why I have a 3k sonic bolt tool to on important fasteners I cannot measure stretch on, it's important to cycle your fasteners because bolt stretch varies greatly and is not proportionate at all.
No one knows what kind of fastener tension it had holding down the cap, this is why I have a 3k sonic bolt tool to on important fasteners I cannot measure stretch on, it's important to cycle your fasteners because bolt stretch varies greatly and is not proportionate at all.
I've made 4 VERY quick drawings. I attached a 2D drawing I made where you can see a 2" bore when the two caps (imagine one is the block and one is the cap) are put together. I then trimmed 0.250" off both mating surfaces. I intentionally took a lot off so you can see the shape it actually makes. The cross sectional area of the journal is now SMALLER. If you reference off the journal in the block when line boring/honing, you will take no metal off the block and you will take metal from the cap. Because the cross sectional area of the geometry is smaller after machining, you can maintain a perfect circle and maintain the original centerline.
Stingpuller, your concepts of machining are wrong and flawed. Along with a few others like I said just think about it. This is a very simple line bore machine operation. Again the finished machine process does not change center line or cam gear clearance period. The only thing that will change is the cap hight and cap mating surface hight in block(if machined). Drawing a picture may help as some have done allready in this thread.
I probably could have just quoted this guy. He had it right and made it an easy way to do a demo for illustration purposes.:thumb:
Question number 2 if we cut the caps when does it become needed to shim under the girdle??
How much do you want to bow it down?
How much do you want to bow it down?
Here is where most of are missing understanding the concept of the remedy. It would be the correct assumption that the center line will change only if it is align honed through the normal methods. To remedy his problem without changing centerline would require us of a cnc vertical mill. Thus a true original centerline could occur. Finding g a shop capable and near you may be more costly than starting over. Both sides have the right perception depending on the appropriate remedy.
Caps
If it has spun a bearing or out of alignment on the mains you will have to cut the block side. If you cut the block side it will change the CL. I don't care how good you are "IF" you cut the block it will change.
If it has spun a bearing or out of alignment on the mains you will have to cut the block side. If you cut the block side it will change the CL. I don't care how good you are "IF" you cut the block it will change.