Engine decking issue(help)
- Thread starter MoparMark91
- Start date
-
Wyrmrider
Well-Known Member
several issues here
first I usually did the trial assembly after line bore (and I do not trust line hone)
I'd have done the rods on the tobin-arp and they would all be the same (maybe bushed to the max for "stock")
.010 is a bunch do the trial assembly with the longest rod/piston combo and find out per YR
using a bridge you can check both sides of the piston to get a hint of square
Cometics require smooth- as YR says all can benefit
out of the hole is ok- you can change the gaskets I have a closed chamber 440 .015 out with .050 gaskets
My shop had the BHJ tooling- most good shops around LA have it but we did just fine before tooling was available- just takes more time
cam tunnels are not always straight with the mains- especially after a quickie line hone
calipers for a quick check but not for low corners
first I usually did the trial assembly after line bore (and I do not trust line hone)
I'd have done the rods on the tobin-arp and they would all be the same (maybe bushed to the max for "stock")
.010 is a bunch do the trial assembly with the longest rod/piston combo and find out per YR
using a bridge you can check both sides of the piston to get a hint of square
Cometics require smooth- as YR says all can benefit
out of the hole is ok- you can change the gaskets I have a closed chamber 440 .015 out with .050 gaskets
My shop had the BHJ tooling- most good shops around LA have it but we did just fine before tooling was available- just takes more time
cam tunnels are not always straight with the mains- especially after a quickie line hone
calipers for a quick check but not for low corners
Wyrmrider
Well-Known Member
lom
that's what shim stock is for
out here in the woods we just wipe off the block and set the quick way on and bore away
that's how we get the bores square with he deck
that's what shim stock is for
out here in the woods we just wipe off the block and set the quick way on and bore away
that's how we get the bores square with he deck
nm9stheham
Well-Known Member
Yes but that is why I measure 4 spots on each piston: top, bottom front and back (with the same piston/rod assembly). For top and bottom, I rock the piston, and take max and min heights, and average between those 2 numbers. It takes a while to carefully measure all 8 cylinders this way.
Lay the number out carefully on a diagram and you can spot trends, like top-to-bottom slopes on the deck that are not right at 45 degrees from the crank centerline, or humps or dips (that seem to be pretty common).
yellow rose
Overnight Sensation
And how do you know how far to cut the decks???? You don't, unless you measure every rod and piston and measure the stroke on every throw and correct all the **** so it's the same.
I'm betting I can use a manual machine and produce work equal to yours with that rottler.
Unreal.
Well, I got news. If you don't think you caint measure deck height with a caliper as I described, you can laugh at it all you want, but you're still wrong.
Wyrmrider
Well-Known Member
rusty
you can measure end for end but hard to measure tilt or a twist ie square x and y
(but then that's what rod pins are for
seriously OP
let's say your pistons and rods are NOT blueprinted
and you find your deck heights are off end for end
you can always swap the pistons around (keeping the exhaust valve notches in the correct spots) and maybe get them closer
this can adjust for both deck and crank throws being slightly off
let us know what you find out
you can measure end for end but hard to measure tilt or a twist ie square x and y
(but then that's what rod pins are for
seriously OP
let's say your pistons and rods are NOT blueprinted
and you find your deck heights are off end for end
you can always swap the pistons around (keeping the exhaust valve notches in the correct spots) and maybe get them closer
this can adjust for both deck and crank throws being slightly off
let us know what you find out
moper
Well-Known Member
Thank GOD OMM posted this.
It's not that everyone needs the equipment - but the shop they use SHOULD have it if performance work is a part of their service. In the early 2000's my shop got their Rottler and it was night and day. The shop I now use has one too for the same reason.
The correct fixture allows for the actual distance from the true crank centerline to the deck surface. That is the only way to actually square deck - that's what the "square" part of the description is.
So if your shop doesn't have that, either use one that does, or if you can't ignore the worry and move on. Use the Felpro gasket and you'll be fine. Only MLS gaskets might leak. And that's a might.
It's not that everyone needs the equipment - but the shop they use SHOULD have it if performance work is a part of their service. In the early 2000's my shop got their Rottler and it was night and day. The shop I now use has one too for the same reason.
The correct fixture allows for the actual distance from the true crank centerline to the deck surface. That is the only way to actually square deck - that's what the "square" part of the description is.
So if your shop doesn't have that, either use one that does, or if you can't ignore the worry and move on. Use the Felpro gasket and you'll be fine. Only MLS gaskets might leak. And that's a might.
yellow rose
Overnight Sensation
No ****? Indicate the bar to the mill. How hard is that?
Some of you make **** way harder than need be.
Glad we could intertain you . Just wanted to tell you to kiss my butt. Not too high not too low right in the groove.
square heads debating square decks. they call me block head. lol
I suspect the machine shop that did mine didn't get it quite right. Compression numbers are within a few pounds on all cylinders but the left bank has average 203 psi and the right bank has 208 psi cranking pressure. The thrust bearing on both my 318 and 408 are always in the worst condition when I change them out yearly. Both motors line bored and zero decked and done in the same shop same machinist...who is no longer employed there.
rusty
you can measure end for end but hard to measure tilt or a twist ie square x and y
(but then that's what rod pins are for
seriously OP
let's say your pistons and rods are NOT blueprinted
and you find your deck heights are off end for end
you can always swap the pistons around (keeping the exhaust valve notches in the correct spots) and maybe get them closer
this can adjust for both deck and crank throws being slightly off
let us know what you find out
You can measure more than end to end. You can measure end to end and at each main bore. True, you cannot measure for twist, but the deck height itself can be measured.
I don't think anyone is debating that it's not good to have the proper equipment. What I'm getting is, there's more than one way to get it done right. And that's a fact.
yellow rose
Overnight Sensation
How many thousandts off does 5 pounds of compression equat to?
I've also never seen 8 cylinders with the same compression numbers.
And, a shitty looking thrust is most likely a converter issue.
And how do you KNOW that 5 pounds of compression is off BECAUSE of the deck height? Good GRIEF.
One side the pistons sit in the hole average .004 the other side sits in the hole .009 on the 408. The 318 sits .012 and on the other .018. same side is low on both blocks.
Last edited:
Ok, not arguing with you but do you think that's the only variable with cylinder pressure?
yellow rose
Overnight Sensation
That's not the machines fault. That's a piss poor machinist. You say your measurements show one engine is .005 off and the other is .006 off? The dude should have been fired and sent to work at a fast food drive through.
There is no reason to be off like that. Other than the machinist was shitty.
Absolutely not. If it was done right the piston should sit nearly equal depths side to side not counting variances in pin location and rod length. Seems odd that both blocks show the same height variance on the same side. tells me they're not setting it up right or their equipment is off. It will contribute to cranking psi side to side as well. Ya know, I may not be too smart but I sure can lift a lot of heavy stuff and I know how to use a depth dial indicator.
Not questioning your intelligence at all.
Yeah I've always said "I have a strong back and a weak mind"
rustycowll69
Well-Known Member
machinists are human, they can and do make mistakes. Sometimes it's the machine, or setup procedure, or the machining technique. It can also be poor training, carelessness, even ignorance.
But a high-zoot machine does not guarantee superior results, or even acceptable results. I once was tasked with diagnosing running problems for a freshly rebuilt 383 4bbl. It had unusually low vacuum, considering the combo. It turned out the valve seats had been cut with a Serdi form-cutter. At first blush, they LOOKED perfect, but in reality, they were not square and concentric with the valve guides, so the valves weren't sealing properly. So I redid the (then)state of the art" cut valve seats, using my (then)50 year old old-school seat grinder. Problem solved.
But a high-zoot machine does not guarantee superior results, or even acceptable results. I once was tasked with diagnosing running problems for a freshly rebuilt 383 4bbl. It had unusually low vacuum, considering the combo. It turned out the valve seats had been cut with a Serdi form-cutter. At first blush, they LOOKED perfect, but in reality, they were not square and concentric with the valve guides, so the valves weren't sealing properly. So I redid the (then)state of the art" cut valve seats, using my (then)50 year old old-school seat grinder. Problem solved.
Listen! I don't mean to put all of your methods down. But times have changed. I can remember not that long ago my telephone had a wire going to it.
It took a long time to get our machines that we have. They are for us and racers we know and meet. My son charges $200 to square deck a V8. Break a tool and there goes a couple hundred
He was telling us tonight the proper way to machine a new block is
1. hold the block and Bore the cam tunnel
2 hold the block by the cam tunnel with a cam bar and cut the mains
3 hold the block in the fixture by the main bearing bores and set the deck height on one side by using the Cam and crank center which is 45 degrees to the first deck. Zero the DRO
4.Turn the fixture and it will go past center to 45 degrees to the other side of the center this will be 90 degrees from the first deck This is square decking. Exact 90 Degree head surface difference is squaring the decks. If you cut to zero on the second Deck they will be the exact same height and 90 degrees apart. Another words a framing square will set from deck to deck. Square!
Now if you have different piston to deck heights you have issues with your rod lengths. They are different or the piston pin heights are off. You never change the deck to fit different height pistons. What are you all thinking? I am not a machinist nor are other members that come here but most of us would know that through common sense . Think about what you all are saying.
Oh yeah we don't need work so I am not trying to get any for him. He cannot get caught up know. But we do help friends in a bind when they are broke. He'll work on a weekend for friends.
Most big name shops have Rottlers/ or "Bed mills", Rottler is a brand name, Top of the line . Take your block where they have the new equipment and and have the fixture for your block.
I have a trivia question. Why did they put shorter rods in number 1 and 2 pistons on a nitro super charged funny cars and rail cars which lowered compression on those cylinders? My son told us this tonight. He learned this working on nitro motors. some are still doing it.
It took a long time to get our machines that we have. They are for us and racers we know and meet. My son charges $200 to square deck a V8. Break a tool and there goes a couple hundred
He was telling us tonight the proper way to machine a new block is
1. hold the block and Bore the cam tunnel
2 hold the block by the cam tunnel with a cam bar and cut the mains
3 hold the block in the fixture by the main bearing bores and set the deck height on one side by using the Cam and crank center which is 45 degrees to the first deck. Zero the DRO
4.Turn the fixture and it will go past center to 45 degrees to the other side of the center this will be 90 degrees from the first deck This is square decking. Exact 90 Degree head surface difference is squaring the decks. If you cut to zero on the second Deck they will be the exact same height and 90 degrees apart. Another words a framing square will set from deck to deck. Square!
Now if you have different piston to deck heights you have issues with your rod lengths. They are different or the piston pin heights are off. You never change the deck to fit different height pistons. What are you all thinking? I am not a machinist nor are other members that come here but most of us would know that through common sense . Think about what you all are saying.
Oh yeah we don't need work so I am not trying to get any for him. He cannot get caught up know. But we do help friends in a bind when they are broke. He'll work on a weekend for friends.
Most big name shops have Rottlers/ or "Bed mills", Rottler is a brand name, Top of the line . Take your block where they have the new equipment and and have the fixture for your block.
I have a trivia question. Why did they put shorter rods in number 1 and 2 pistons on a nitro super charged funny cars and rail cars which lowered compression on those cylinders? My son told us this tonight. He learned this working on nitro motors. some are still doing it.
-
