Damaged crank flange

-

pishta

I know I'm right....
Joined
Oct 13, 2004
Messages
23,815
Reaction score
13,670
Location
Tustin, CA
Had this 340 turned mains 360 crank forever after Fedex damaged it in shipping. Didnt want to toss it so Im doing a derust session on it. I realized the chip in the flange is not as bad as I remembered it being, its just a corner chip between a bolt hole and the void. If I were to actually put a bolt in whats left of that hole (not even sure it would hold one) and then run a flexplate, do you think the strength would be all that reduced? It would be a hack 318 stroker build (cleaner than UTG/Nicks motor at least!) using low compression cast truck pistons and open 360 heads and the thickest pair of head gasket I can mic out of the 13 I have collected at various swap meets. The chip and the location:

chips.jpg




crack.jpg

Figured I could at least epoxy it and put a bolt in it with locktite red 271 just for the balance of it if it would matter being so close to the axis? Looks like crack is not on thrust side of flange it that existed.
 
Epoxy will never hold it. You can have it pinned and welded though.
 
Weld it. It'll see some centrepital force. It's the friction when the bolts tighten the flex plate or flywheel that carries the majority of the load. Got room for a nut on the back?
 
Weld cast iron? The epoxy was just to keep it in place before the clamping of the flex plate would capture it. No nut would fit. Maybe braze it with oxy-acetelyne and bronze rod?
 
Weld cast iron? The epoxy was just to keep it in place before the clamping of the flex plate would capture it. No nut would fit. Maybe braze it with oxy-acetelyne and bronze rod?

Hell yeah it can be welded. You been readin too many forums. lol
 
Don’t bother welding it. The bolts only hold the flywheel from spinning. The ring in the center keeps the flywheel on.

I’d put 5 quality ARP bolts in it and run it, unless you are making 2 HP/CID and/or spinning 8500.
 
I think it would be fine just to leave it out and run it. I woudlnt risk it breaking off again while in the engine!
My biggest concern would be what would that missing piece do to your balance?
 
As a certified welder by trade- I would not touch it. A few reasons:
A) balance will be off.
B) if cast - weld cracks after the weld and that piece letting loose at 5000rpm would be like a bullet. 50/50 chance though.... centerline down hits the ground centerline up its all leg. Liability is crazy.
C) bolt loose up. After welding you need to retap threads cause they will be off. Could cause issues.
D) what you will spend on welding it properly with no guaranty, your possible in the replacement crank range.
Not worth the energy - make it a display item. Tell people it came from a motor that set a world record and not worry every time it runs “will today be the day.”
Just my humble 33 years as a professional welder opinion.
 
Last edited:
As a certified welder by trade- I would not touch it. A few reasons:
A) balance will be off.
B) if cast - weld cracks after the weld and that piece letting loose at 5000rpm would be like a bullet. 50/50 chance though.... centerline down hits the ground centerline up its all leg. Liability is crazy.
C) bolt loose up. After welding you need to retap threads cause they will be off. Could cause issues.
D) what you will spend on welding it properly with no guaranty, your possible in the replacement crank range.
Not worth the energy - make it a display item. Tell people it came from a motor that set a world record and not worry every time it runs “will today be the day.”
Just my humble 33 years as a professional welder opinion.
A was the first thing that came to my mind! But the others are valid points! I didnt even think if it becoming a projectile!
 
If you were closer I would give you a 360 crank.
 
If you weld it right it will hold but the heat from welding and the cooling will warp the crank and will need ground to get straight.
 
If it comes to it, ill just cobble the weight and run it. Im not that concerned about the projectile issue as the flex plate shrouds this area. The 'value' of this crank is that its already turned down to 340 mains ($$) so its technically a 318/340 3.58 stroker crank. Just another 'scrape a motor together and see what it can do' idea.
 
The bolts not only retain the flywheel or flexplate/TC, but also firmly clamp them onto the crank flange. That becomes more important as you get to higher power and higher RPM's and the torsional crank vibrations start to emerge: loose bolts there will worry out the threads/hole. But if you are just foolin' around with this engine, you can probably get by with it. Or put in a 5/16" dowel and matching tight fitting hole in the flexplate flange nearby.

Imagine taking a chunk that size out of the big end of 1 rod on the 7-8 journal.... that is what you are talking about with balance change. It will have maybe 1/3 or 1/4 of the effect of the weight on the TC of external balance 360, since it is about 1/3 to 1/4 to distance from the center line.

So not trivial but not huge if this is just a 'foolin' around' engine. You could tack about 1/4 to 1/3 of the weight out on the TC at the same crank angle and make up for it.

I like your engine parts combo. That is clever thinking for a low buck 318 stroker. How many cubes is that?
 
343...360 with a .090 undersized piston. is there a formula for tacking that weight on the flexplate, ie. 1/2 the weight at 2" as opposed to 100% of weight at 1" (not broken). I could easily make that weight appear on the flex or convertor if there is a formula for 'oz/in' with the 'inch' as the variable.
 
Unless you are throwing a ton of horsepower at it, I'd run it & not think twice about it.
 
I'm no expert, but the change in balance would be so very minimal with something that small and that close to the centerline of the rotating mass?
 
Just do as yr said and run it
bolt circle is so close to the crank center it is not going to have much effect
no welding or chance of loose parts

I guess you could add a bolt between the break and the next good bolt
how far apart are the bolts on a 8 bolt crank?
 
Weld cast iron? The epoxy was just to keep it in place before the clamping of the flex plate would capture it. No nut would fit. Maybe braze it with oxy-acetelyne and bronze rod?
It's cast steel not cast iron....you can mig weld it.
 
343...360 with a .090 undersized piston. is there a formula for tacking that weight on the flexplate, ie. 1/2 the weight at 2" as opposed to 100% of weight at 1" (not broken). I could easily make that weight appear on the flex or convertor if there is a formula for 'oz/in' with the 'inch' as the variable.
Exactly... the weight goes down by the same factor that the distance goes up. So if is is 2 Oz at 1" then you would tack on 1 oz at 2" or 2/3 oz at 3" and so on. You'll have the bolt weight missing too.

It is what is called a 'moment'.... weight multiplied by distance. Just keep it constant.
 
BTW, Pishta, what are you doing about overall balance here? You are putting 318 pistons and later heavy rods in there? The bobweight is not going to be quite the same as for the 360LA piston setup... maybe 15-20 grams off. Just run it?
 
Might be a good idea to grind smooth the cracked area to reduce likelyhood of further stress cracks. I would........run it with 5, that is.
 
-
Back
Top