patman

iTrader: (3)

Well, I just managed to crack another iron. This time it was my thick center iron on the 20B. Since they are so hard to find, and I am broke, I am planning to just weld it back together. I am also considering adding some bracing in the dowel pin lands on all my irons. My basic idea was to make some triangular gussets out of 1/4" stainless plate, and add a couple to each iron. I had thought that this was just one of my crazy ideas, but I have been told that old school racers used to do something like this pretty often.

My question is, who here has done something along these lines, and how well did it work? Also if you don't mind sharing, I'd love to know how exactly they were reinforced, or to see some pics....

Thanks,

Pat

BLKTOPTRVL

Can't answer your question. But I am curious... Do you know why they are cracking?

RacerXtreme7

iTrader: (2)

STUD the engine, no not replacment studs replacing stock bolts, but get all the irons and rotor housings machined and use the large size, low clearance stud kits. Mazda Trix and Guro offer them. Say BYE BYE to cracked irons.


~Mike.............

patman

iTrader: (3)

i broke the rear iron on my 13b due to a broken engine mount at 165mph, causing the motor to twist apart.

I am not sure on the 20B, I don't know exactly when it cracked, but my guess is I got a bad tank of fuel and detonated it. I gotta get a knock sensor and wire it in to my ECU...

I thought the 20B was pretty bulletproof...I added 3 dowel pins on the rear 2 rotors, and 2 on the front, and I am only making 600whp, running 17psi, but I guess that was a little too much. It was hot as **** here all last week too, which I'm sure had something to do with it.

patman

iTrader: (3)

Mike I would love to make myself a set of 12mm 4140 studs, I have been thinking about it for a while, but the problem is that I already doweled the engine, so some of the holes are bored way too large... I guess I could fill them with something, or just make new dowels with a larger ID, but I'm not sure if that is a good idea. What do you think about it?

RacerXtreme7

iTrader: (2)

Hmmm, already bored for dowels huh? Well, I'd suggest a safer tune once you get it back together then, I guess making some spacer for larger studs could work, but now all your machining tolerances will have twice any error but any competent machine shop should be able to handle it. I don't know if running spacers and studs would be a good idea though, any deflection from the stud will be transmitted driectly to the spacer/dowel and now there is less material in the irons. At least with the dowel only the smaller tension bolt is a LOT smaller allowing movement of it. Back off the timing and a couple psi of boost (MY GOD over 550 hp in a street car has got to be just plain useless {umm tire smoke}). When your feeling froggy and go to the strip poor in some race fuel and bump the timing and boost back up.

~Mike.................

crispeed

Sorry to hear about this.
When you get a chance remove the stationary gear from the housing and inspect the area where the bolts go to. The casting in that area is very weak and proned to cracking also.
What series was your 20B?
do you have any pics of the cracked housing?

patman

iTrader: (3)

competent machine shop, lol. I do all the work myself, so that's not gonna happen. Race gas is also a no-no. My basic premise for this car is that I do all the work myself, I drive it to work when I feel like, and I make it as fast as possible. I guess I'm trying to prove that an FC can be that fast and powerful and still be drivable and affordable. So I don't ever plan to run anything higher than 94 octane, and I don't buy any expensive parts. My sorta goal is to make 700whp and run a sub 10-second 1/4, while maintaining good handling and at least 15mpg. I figure I'm almost there on everything but the 1/4, as I can't afford axles and a diff right now. Perhaps this is a fool's errand, but that's fine with me.

also, it looks like my own stupidity is what caused it...i filled it half way up with 91 octane last week when it was 104* outside, then took someone for a ride on high boost. I hate these gas stations that have 91 or 92 in their premium tank. Shoulda paid more attention.

anyway, I pulled the motor this afternoon, so I should be able to pop it apart tomorrow sometime and see what Ive got to work with. I still haven't ruled out the stud option....

Japan2LA

iTrader: (256)

Sorry to hear that.... STUD KIT STUD KIT STUD KIT...

patman

iTrader: (3)

it is an A series, and I already ran a bead over the crack, so no pics. It was just a small crack about 3/4" long running right over the front dowel land on the thick center plate.

Japan2LA

iTrader: (256)

A Code motors= non-reinforced dowel pin area side plates.. I actually just compared a set of A code 20b irons to a set of D code and the difference is huge..

Another issue you may run into.. I know a sandrail guy with an A code motor.. no stud kit.. making about the same HP as you.. cracked the thick plate once, had it welded, ran the buggy again and craked it again in the same spot but worst the second time.. seems like once it cracks it becomes the absolute weak link...

patman

iTrader: (3)

hence why I am asking about adding material and bracing to that area....

At this point, it is either try my luck with that or park it until spring, there is no way I can afford a new center iron... Building a car like this on a college kid budget was never a really great idea....

Japan2LA

iTrader: (256)

If you have the patients to part it out, then you should be able to make enough money to pick up a D code or C code... longblock

Or just source a set of Newer style side plates C or D code

patman

iTrader: (3)

if i was going to do that i'd just get a new center iron and use 13b parts for the rest

RXBeetle

Out of curiosity how are you welding the Irons? I was under the impression that welding cast iron was really tricky to do and still retain strength, like you have to get it really hot and use filler rod just for it. I've done some half assed TIG welding stainless pipe to a cast iron manifold and it was shitty. Sealed yes, but I wouldn't consider it structural.

patman

iTrader: (3)

i will probably take it to the shop where I used to work and weld it with a nickel rod.

I have some spare irons laying around, I will also try welding on one of them with a MIG and stainless wire. I have had excellent results with welding cast iron that way in the past.

Zero R

iTrader: (1)

You can sleeve the dowel pinned holes to accommodate the studs, I have had to do it here for just about the same reason for a customer and it works just fine.

Kyrasis6

lol, good luck on the welding. Welding cast iron for anything other than cosmetic reasons is a garanteed failure, it puts more stress in the surrounding metal than what was there to begin with which is why cast iron will always crack again near the point of the weld.

I've heard of some people grinding out an area around the crack then making a small casting to go around that area of the part, casting it and then machining the nessesary areas. I'm not sure if this will work in your case but I wouldn't even attempt to weld it. Joe Mondello makes this zinc alloy stuff they use for filling in areas in cast iron cylinder heads it might be worth trying.

http://www.mondello.com
Part number: ZA12
Zinc alloy for filling heat riser passages in early heads. You need a cast iron ladle & natural or propane gas burner to heat this product to 810°, stirring for 2 minutes to mix well before pouring into the area you want filled. You only have one chance. Do not under fill the area; it will not stick to previously poured ZA-12. $5.00/lb.

Joe Mondello
Mondello Tech Center
2470 Pomona Road
Crossville TN 38571
931-459-2760
888-MONDELLO
(888-666-3355)

patman

iTrader: (3)

we'll see. it is all welded up now, and my viton coolant seals should be here tomorrow. I have decided to hold off on studding until winter so I will have more time to drive the car this fall. I figure doing the machine work between work and classes would take me a month or so, and I don't want to miss the best part of the year.

kryasis I was thinking about stress relieving the iron, but the guys at the shop said they didnt think enough welding was done to require it.

when i do stud it I will be using 1/2" 4140 cold drawn rod. This is less than half the price of 12mm here in our backwards country, and should work just as well. The CD rod that my shop stocks is +0 -.002, which is probably a better tolerance than I will get reaming the irons anyway. The whole project looks like it will cost me about 20 hours and $200. I may post up a writeup when I do it if anyone is interested....

Pat

TonyD89

iTrader: (10)

I tend to agree that the welding of the iron is risky. I don't think your going to be happy in the long run.

Dowel pinning the motor is probably the strongest and is tried and true but I have an idea and was wondering what you guys think. What about adding short dowels between the plates in a few spots near the factory dowels. Using only a half inch long ( or longer, especially into the housing) swiss dowel with an ID that clears the tension bolt and not machining the hole all the way through the plates and housings. I am sure I could hold accuracy buy working off the factory dowel and using a CNC machine. The advantage being cost and the of using store bought dowels. Don't have to make anything just machine the diameters around the tension bolts.


Just an idea. I don't plan on setting any dyno records just looking for added safety factor.

Kyrasis6

Stress relieve it.

I've never actually looked into how doweling is typically done. I was just going to get some stainless 1/2" or slightly bigger 304 stainless rod, machine it for a wall thickness .060" bigger than the tension bolt holes, cut it into 1" lengths, drill it and then machine the rotor housings for a press fit. I was going to put one into every tension bolt hole I figured that would be more than enough to keep the block from flexing.

How is it normally done?

Edit: Forgot to mention that from my experience with piston racing engines shorter can be better in applications like this since it reduces the amount of leverage the moving parts can exert on the pin thus making it harder to crack in a weak spot.

patman

iTrader: (3)

Dowel pinning is certainly not the strongest, studding is. I doweled mine by adding more factory dowel pins (which were free, and already the right length) I assume it worked to some extent, because I have 3 extra dowels on the center and rear housings, and only two on the front, and thats the one that broke. Obviously it is not a perfect solution though.

The other major problem with doweleing a 20B is that the castings on the center irons are not very thick, so you do not have room for much of a dowel. I had to turn the ends of the factory dowels down to get a compromise size.

As mentioned above, I would NEVER spend all the time and hassle to dowel an engine again. every high output rotary I build from now on will have 1/2" studs replacing the tension bolts. I just don't want to mess with the downtime right now, so I am hoping that this weld will hold until winter.

TonyD if you are going to do that, do like kyrasis has mentioned and use 1" dowels on every tension bolt hole. I considered doing something like that, but I don't have a lathe and didnt want to have to spend the time in someone else's shop. Plus the studding thing makes more sense, and is also proven, and I can do it myself.

I can't argue with experience, but a shorter pin also reduces the amount of contact area to absorb the stress, which means more of a stress concentration. I would think that that would cancel out the leverage issue, but it's hard to tell things like taht sometimes.

Kyrasis6

Yea, it could go both ways, that's why I figured it would be better if you where going to do it that way to do all the holes and not just some of them, then you are distributing the forces across the entire part instead of a large area localized to one spot in the part.

Was also thinking about previous experiences, anybody doing it this way would want to machine the holes with a tool so they had about a .030"-.045" radius in the bottom because if it where going to crack doing it this way that would most certainly be the place it would.

patman

iTrader: (3)

well the other thing is that there is an unequal force distribution around the housings....the area by the plugs is the only area that sees peak cylinder pressure, then you have a slow pressure drop to about the bottom of the housing where the exhaust port opens, then not much pressure back to the compression stroke. So the area that really needs to be reinforced is the area around the plugs, which may see 3000 psi in a boosted engine, and 2-3 times that for very short periods under detonation. That is a shitload of force!

Kyrasis6

True but is that typically where they crack?