Block girdle questions

[Beck]

I am about to have a girdle made for my little tractor motor. Experts have said the power output of my engine can quickly overcome the strength of the bottom end. Others have said that all a girdle does is keep the pieces together after they come through the pan, making cleanup easier.

A girdle for my motor is fairly easy. The main caps and the pan rail are level, so the girdle will be mounted to the bottom of the block, at the pan bolts, and the mains. There will be openings for the crank, rods, and oil pump.

I am considering an external oil pump which would allow a crank triggered ignition. If the oil pump stays in the pan, I have to keep the distributor which drives it. The opening in the girdle for the pump should not weaken it greatly.

I am a concerned about choosing the correct material of construction. My current thought is plain ½" thick steel plate.  2 questions –   1) Is ½" thick enough?    2) Should it be some special alloy?

[Bruce Dorsi]

Are all the main bearing caps the same height?

Will the caps be bolted down under the girdle, or will the bolts go through the girdle?

[Beck]

Are all the main bearing caps the same height?

Will the caps be bolted down under the girdle, or will the bolts go through the girdle?

The caps are all the same height.

I will stud the block for the mains, put the caps on, add the girdle, then the nuts to hold it all down.

[chimp koose]

As I understand it a girdle will really only help stabilise the caps if you have seen fretting  ,or movement of the caps (loosening )in the registers . If you really want to strengthen the bottom end , make a one piece girdle that incorporates all the main caps in a single piece like on old Donovan hemis .That would require some serious hours of machine work but would add some rigidity to the bottom end.

[Beck]

As I understand it a girdle will really only help stabilise the caps if you have seen fretting  ,or movement of the caps (loosening )in the registers . If you really want to strengthen the bottom end , make a one piece girdle that incorporates all the main caps in a single piece like on old Donovan hemis .That would require some serious hours of machine work but would add some rigidity to the bottom end.

Mine will be a one piece that does tie all the mains together.

[Crosley.In.AZ]

Girdle should help.  If the block material gives away from stress , not much you can do about that

[Beck]

A programmer/machinist, distant family member, picked up the pan today to use for the outside pattern and pan rail bolt pattern. He isn't a car guy so this may be interesting.

[wayne petty]

so many ways to go.

https://www.google.com/search?q=block+girdle&newwindow=1&source=lnms&tbm=isch&sa=X&ved=0CAgQ_AUoAmoVChMIq8ir8IWgxwIVRTGICh0xHwGK&biw=1443&bih=875


one member on another forum took a bunch of bolts that fit every oil pan rail and main cap position..  machined the heads off leaving a point after careful calculation.. and use of washers and lock nuts..  was easily able with just two guide holes drilled and long studs installed.. used a big rubber mallet to dimple the steel plate to transfer the marks to drill the holes in the proper position on his drill press.

there was some discussion on that forum years ago about using split tapered cones into the thick block girdle..  same kind used on truck axle ends..   the caps are held down by washers and nuts. fine tuned by grinding the washer thickness.. or nut thickness slightly.  this locks the studs in place tighter into the girdle.. but the holes have to be perfect or it will exert side forces on the main caps..   i worried that the expansion and contraction of the block and the girdle may crack or distort the main caps or screw with the alignment.  

with a big caliper.. one might want to dip the new plate in boiling water in the turkey deep fryer.. or in the barbcue..  heating it up to operating temp.. then a quick measurement between several far apart bolt holes.  see how far is actually expands..  another guy mentioned that putting a little extra width on it.. but keeping it inside the pan rails and getting a 10 to 30 degree bend on a press break will keep it a lot more stable.

[Beck]

I am on hold for a little while on the girdle. A fellow Mercruiser builder built a girdle for his block. He may still have the measurements. If I'm lucky they are for a CNC mill. He has had a health hickup and I am waiting for his recovery to see what he may have.

A big debate on the forums is what is the right material of construction. A lot of the guys are bashing aluminum. It would expand at the same rate as my block. It would need to be much heavier built for the same strength. I don't have any excess room so I am planning on steel.

[chimp koose]

If you are planning to boost this motor with turbo or blower you might want the aluminum. Far better to have the aluminum move a bit then have the main studs crack the webs or try and pull out . You can always re hone the main line but its worse if the main webs crack in the block. Besides that , when you build it you cant make the mains wider but you can make them THICKER making the material strength kind of a non issue . Also your brother in law machinist will thank you as his machining time will be greatly reduced !

[Rrumbler]

This is not really cogent to the discussion at hand, just a bit of comic relief.  

It's funny how something can override knowledge and sensibility sometimes, and I certainly know better, but-----.  The first thing that trampled through my mind when I first read the title of this thread was a nice piece of one inch trench plate, a gas axe, a grinder, and a drill press; keeping with the old "bigger hammer" theory, I suppose.

   

[wayne petty]

that's great..

in my mind.. its just to keep the harmonics from shattering the block..


back in the 90s i had a heated discussion about fully counter weighted cranks..  instead of heavy counterweights on the end to balance them.  

at low to moderate speeds  heavy ended cranks work great..  but get to the higher RPMs. the unbalanced middle of the crank starts whipping.. when it reaches the harmonic frequency of the crank and rods.. the whipping is amplified and the whole mess dumps on the ground..

i was looking for the image of the magic muffler fiat driving over the crank.. rods a few pistons and the oil pan at lions in the late 60s or early 70..

[river1]

borrowed from http://www.dragracingonline.com

[Beck]

That is exactly what I am trying to avoid.
(He-he-he I want it to stay in one big piece when it comes out the bottom)