Block out of square

-
I feel it’s “extremely unlikely” the out of square condition at the back of your block has anything to do with the block machining that was done as part of the rebuild....... unless they machined the bellhousing flange itself out of square.

It would cost a ton of time and $$$ to try and correct all the stack up problems that would follow that big of a screw up.
You’d just throw the block away and start over.

Like I said earlier......what timing set are you going to use in that situation?

If you’re comfortable shimming the bell housing......I say go for it.
 
I had forgotten about this statement in your first post:

"From there, my observation is that the bell itself has a scalloped shape compared to the block. Thus, there's only actual contact in the area around the mounting bolts. Between the bolts, the bell doesn't touch the flange at all. So my next thought it to get a set of precision shim washers, in a range of thicknesses, such that as a set, they make the amount of ramp I need to bring the mounting surface back to true. At that point, I believe my dial indication comes out at or near 0, the angular misalign is corrected, and I should be good to proceed."

If the bell mounting surface is scalloped like you state and only makes contact around the bolt holes then washer/shims should work?? Just to make sure though I would place the bell on it's face (rear face side down on a flat surface) and use a good scale to see if the front and rear surfaces are parallel. I can measure within .015 with a good machinist scale. If the surfaces are parallel then shims should do the job!! You then might need to use silicone (or something) to fill the gaps so that you don't get any rear main oil splatter from coming through the gaps. One reason the flanges are dead flat is for structural strength but also to create a seal. Treblig
 
Last edited:
Treblig said:
1.53838" if my trig calculations are correct???
Click to expand...
Uuuuh off by about a factor of 10... try 0.1536.... still a LOT! LOL

I just checked the dimensions and that .04 degree number really should be around .33 degrees just like PRH has listed. (Arctan of .046"/8") So that would be .126" at the crank snout (sin 0.33* x 22") and more like .103" at the front cylinders.

Is a compression test all that hard to do here? That would answer the question; cylinder pressures would change 20-30 psi with .100" change in the relative deck.

Shims....
 
Last edited:
nm9stheham said:
Uuuuh off by about a factor of 10... try 0.1536.... still a LOT! LOL

I just checked the dimensions and that .04 degree number really should be around .33 degrees just like PRH has listed. (Arctan of .046"/8") So that would be .126" at the crank snout (sin 0.33* x 22") and more like .103" at the front cylinders.

Is a compression test all that hard to do here? That would answer the question; cylinder pressures would change 20-30 psi with .100" change in the relative deck.

Shims....
Click to expand...
I won't disagree because the on line calculator wouldn't let me type in inches for the "22" number so I'm not sure about the answer.

Right triangle Calculator
 
Gotta wonder now why the builder did not catch this.... although not checking it would not be a surprise, as you don't expect the rear face to be out of square. I know I have never checked it on any engine.
 
Jason Wenger said:
0.4 deg :)

Think with congruent triangles. If I have 40 thou of error out at a distance of 8" (rough size of bell), then out at 20" (lenght of block), it's about 100 thou.
Click to expand...
What you write makes sense but i don't understand why the on line calculators keep giving the wrong answer??? When I punch in .040" rise over 20" the calculator says .114" which is what you are saying.
 
“.4” ...... not “4”

Just move the decimal over.

It would cost 20+ times what the block is worth to try and correct all the stack of problems you’d create by line boring the block .32* out of parallel.

It would just go in the scrap pile.

This issue is not the result of a machine shop line boring the block.

Furthermore, if the OE caps were retained....... it likely never had the main line touched..... and if it was, it would more likely have just gotten a quick hone.
 
All you need to do is to remove the main caps and see the irregularities between the bearings and the bearing saddles.
 
I know it was align honed.
Click to expand...

Because they said so, or because you’ve had a main cap off and saw the honing marks in the cap?
Or.......you were there when they did it, in which case we wouldn’t be having this discussion.

Either way, it’s not getting line honed .032* out of square.
 
Treblig said:
What you write makes sense but i don't understand why the on line calculators keep giving the wrong answer??? When I punch in .040" rise over 20" the calculator says .114" which is what you are saying.
Click to expand...
Start with your online calculator set for a format of '2 sides' and enter .040" rise (a) over 8" run (b), which is what is at the back for the block. I get 0.32 degrees from that same calculator.

Then change the format to '1 side and 1 angle', enter that .32* angle (angle a) and 22" for length b, and you get the right answers.
 
toolmanmike said:
@krazykuda , do know the sequence the block surfaces are machined? If a un-machined casting is set in a jig, what surface is machined first? Is the block removed from the jig and set up in another machine for other operations. My point being, If something was wrong from the start, all the dimensions would be off if the block remained in the same fixture during the process. If the machine shop line bored, square decked and bored the block to correct issues the bellhousing surface was left untouched. Bores and decks are dependent on the pan rails being correct. also the main saddles are used. I am just trying to see where in the process something could have gone wrong.
Click to expand...


On the assembly line machining, they usually mill the oil pan rail and get that as your first surface.... That is done from cast datums... Once the oil pan rail is milled, The oil pan rail becomes the datum for up down... They then cube everything off of that surface... Then they make the manufacturing holes to set the x-y planes off of those... Then the manufacturing holes are the datum for the side to side and front to rear...

The oil pan surface determines the up and down axis for the crank... The crank axis center line side to side is controlled off of the two manufacturing holes.

The rear face of the block is cubed from locating on the oil pan surface...

How was the OP block made... It was a crate motor and did they machine the blocks from raw castings or off of "junkyard" used blocks and then machined to clean them up...

The goal is for the crank axis to be perpendicular to the rear face of the block...

The transmission needs it's axis perpendicular to the front face of the transmission that mates to the rear face of the block.
 
Build a stout fixture that bolts to the crank flange with an adjustable tool on the end, rotate the engine by hand and reface it. Presto, the bell housing mounting face of the block is now square with crank flange regardless, no engine disassembly required. Granted such a procedure could be fairly time consuming, likely requiring light passes, but as opposed to what? Complete disassembly and a trip to a machine shop plus reassembly time, or just starting from scratch with another block?
 
Or just use one of these with really coarse paper 40 grit to sand down the high sides until everything is on the same plane??

shopping?q=tbn:ANd9GcQpx8z-TOBx1noh5FZjx5poJ08llNdIrQYF-HT_BLDiQNa1ExevSQ&usqp=CAc.png
 
^^^^^^ Risky. It is out of square already... :)


What I mean is: I wouldn't do anything with just my hands...
 
I was assuming that the sander was a joke. And I think it's hilarious.

80 grit might work better.
 
Being a machinist I was only halfway joking. I know that I could sand it down with progressively finer sand paper then use a very large flat file to get it within .005" of where it should be. Since the OP already has a proven method on how to check for out of square he should be able to know when it's good to go. But then again, I'm a machinist, and I've had to do even more difficult things with fewer options. the flat surface of the belt sander would make it pretty easy to maintain a flat surface but you have to know what you're doing????
TRUE STORY------I bought a Chevy Vega back in the70s, it had a bad head gasket. Engine wouldn't run at all. The old Vegas had an inline aluminum 4 cylinder that had what are called "floating cylinders". The floating cylinder had a tendency to shift and shrink causing head gasket leaks. I pulled the heads, put a straight edge across the tops of the cylinders and found that the two center cylinders has sunk about .060" down into the block. I took a 2 X 4 and some coarse sand paper and started sanding down all the high spots on the top of the block. Of course I filled the cylinders with rags first to keep them clean. Either way, after a few hours of sanding I managed to get it pretty darn flat using my 18 inch straight edge and feeler gauges to verify the flatness. I bought a new head gasket, installed the old head, started the engine and drove the car for 5 years with no issues until I sold it. I told the buyer what I had done and he said, "No problem, at least if I blow another head gasket I'll know what to do." Treblig
 
^^^ LOL. Well, actually, I straightened out a pretty baldly warped /6 exhaust manifold 2 years ago with a belt sander; took my time and kept checking with a known rigid straight edge (checked to be to under .001 over 2'). (The process of grinding that way does not seem any different that a blanchard grinder.) And lathe ways get trued up by hand scraping. I've done other mods by hand methods. It is not a .0005" accuracy method, but you don't need that here. Gotta go gradually and not overheat the metal. Certainly doable if you want to trade time for $$; not any worse than shims IMHO.
 
redlined said:
Build a stout fixture that bolts to the crank flange with an adjustable tool on the end, rotate the engine by hand and reface it. Presto, the bell housing mounting face of the block is now square with crank flange regardless, no engine disassembly required. Granted such a procedure could be fairly time consuming, likely requiring light passes, but as opposed to what? Complete disassembly and a trip to a machine shop plus reassembly time, or just starting from scratch with another block?
Click to expand...
That is some good thinking and I just thought of a tool I have used for a similar thing.... link is below . It is used to grind down the exhaust ports on light aircraft engine to get them straight after they get burned and cut through buy exhaust gases and the exhaust flange gaskets no longer seal. You would not need anything that sophisticated here.

Pneuport Resurfacing Grinder
 
redlined said:
Build a stout fixture that bolts to the crank flange with an adjustable tool on the end, rotate the engine by hand and reface it. Presto, the bell housing mounting face of the block is now square with crank flange regardless, no engine disassembly required. Granted such a procedure could be fairly time consuming, likely requiring light passes, but as opposed to what? Complete disassembly and a trip to a machine shop plus reassembly time, or just starting from scratch with another block?
Click to expand...

I really like this idea. Perfect way to get the back face back square to the crank. Now I just need to spend some time figuring out how to mount it all. Thanks for the great suggestion.
 
You must log in or register to reply here.
-

Back
Top