RXBeetle

I decided to take a stab at adding more dowels to My housings to prevent them from cracking at the oil filter stand area. I will be making my own hollow dowels out of tool steel with just enough clearance for the housing bolts to go through them. The dowels will be 9/16" dia. and an 1.5" long. I'll do my best to cover the steps of the process

1. I turned a pin to locate the center of the bolt holes in the housing
2. clamped the housing to the mill table with the pin in the collet.
3. I used a 1/2" carbide end mill to break the surface of the housing. I have already had the housings ion nitrided and is very tough to cut into the surface.

RXBeetle

4. I lucked out and found an end mill that was just a couple thousandths under 9/16" and I used it to open the hole in the side housing.
5. I cleaned the face of the clamped side housing and placed the rotor housing on it then inserted the oem dowels. Next was two more clamps holding the rotor housing to the side housing/table
6. I used a long 1/2" end mill and slowly opened up the rotor housing bolt hole. (remember nothing was moved, the same hole center is being established in the rotor housing now).

RXBeetle

7. I forgot to snag a pic but I used a 17/32" drill bit to open the hole in the rotor housing a little more before reaming.
8. Ream (Everything drilled, milled, reamed 3/4" into the rear iron for lots engagement)
8.1 use generous amounts of oil and make sure there is room under your setup to allow the chips to flow out with the oil.
9. repeat as many times as you like, I just did the two bolt holes right next to the factory dowel pin.

Next step is making the dowel pins. I'll be sure to get pics of that. I'm hoping to do final assembly on Christmas.
Pin
OD: 9/16"
ID: 0.390
Length 1.5"

Questions / comments welcome...

RXBeetle

Couple more pics;
1st: both holes reamed
2nd: engine bolt just to get a visual of how thick the dowel pin wall will be (~.086")

TonyD89

iTrader: (10)

This may be a dumb question, but:

Why the two holes next to the factory dowel? No argument on why not those two, though. Just wondering. Is that what you've seen or heard from other people?

RXBeetle

Typical failure point on higher hp motors, especially NA motors like mine.
http://www.rotaryresurrection.com/2n...ron_break.html

TonyD89

iTrader: (10)

I suppose I should have been more specific. Or maybe the answer is the same.

Such as going diagonally opposite as to create an "X" pattern. Or going to six, equally spaced like a bolt circle instead of just around the dowel.

RXBeetle

never mind..

RXBeetle

There is very little force exerted on other areas of the housing. Dowels or studs all the way around would be reinforcing the intake and exhaust are while the really high forces (combustion) are happening in only one area. I could add more dowels along the combustion area but I think the two should be sufficient for my power goals. If this was a 500hp 9000 rpm race motor I would dowel the crap out of it. But its going to be a ~300 hp motor pushing a 2000 lb. VW beetle around. I have put a LOT of work and money into this motor and this is just a little insurance and piece of mind.

diabolical1

iTrader: (3)

very impressive, as always. this was also very enlightening. all this time i always thought that the stock engine dowels were used when doweling an engine. i mean i always knew it was a process that precision, but i had no idea that the dowels were fabricated.

RXBeetle

Thank you. You probably could use stock dowels but they are pretty large and would leave very very little material in the rotor housing to support them.
I made the dowels this morning out of S7 Steel which has very good shock strength. The lathe was not real happy cutting it, especially considering the only round I could find was 1" dia. I turned it down to within a few thousandths of 5/16" and then set it up in a rotating fixture on the surface grinder. These things are size for size so it will be pretty close to a press fit. I will also be using Loctite 641. S7 can be air hardened so I hit em with the acetylene torch and they are hard as hell now. If something is going to break It won't be the dowels.

Rx7carl

Intersting stuff, thanks for sharing.

TonyD89

iTrader: (10)

Nice! I really like the idea of keeping the diameter down to retain strength in the housing. A little draw on those dowels to get that S-7 off its max hardness will greatly increase its strength.

Turblown

iTrader: (12)

A lot better route than using stock dowels..

RXBeetle

I just got the engine together today. This is my first rotary build so I took every thing very slow and followed the Atkins video. Pics below.

RXBeetle

Side note, oil control seals are sharp as hell. Atkins reminded me of this about 5 seconds after I sliced the hell out of both thumbs.

Y2D

I heard you go every second bolt hole going downward from the top one, the big pressure isn't when it compresses, it's at and after TDC... I have the reamer for the factory dowels... 16mm... now, i do agree that it doesn't leave all that much meat around them, but of the flip side the pressure is against them, not pulling on them.. as for the material used.. I think that as long as it doesn't rust too quickly, face it, if you add 2 or 3 dowels, the shear strength of them, even at 1/2" diameter, is HUGE... remember, it would have to shear on the front and back side of each housing... the point of the dowels is just to spread out the load on the cast parts... In my humble opinion, putting two of them at the top will help prevent the castings from cracking, but doesn't do much for for the root cause of the problem.. then again.. you say this isn't s superpower engine, just want a little more reliability for 300ish HP, which I think your job will accomplish nicely

Mahjik

iTrader: (1)

lol, don't worry. You only do that once as you have a little painful reminder not to do it again.

patman

iTrader: (3)

I know this is an old thread, but someone linked me to it and I just wondered how this worked out in the end? It looks like you did a pretty good job, but the small diameter of those dowels worries me as it would cause a huge amount of bearing stress in the rotorhousings...so I'm hoping you can report back and prove me wrong!

Pat

RXBeetle

Unfortunately I haven't gotten very far. I have a lot of work to get done on the car before the engine is ready for some abuse. Between a full engineering course load and work to pay for those courses I am lucky to sneak a Saturday or Sunday night in. I am redoing my cooling system and I had to make Trans mounts to squeeze the Porsche 901 transaxle in my Beetle and move it up 1.5" for better oil pan clearance before I could even test fit the engine (see attached pic). It all mounts to the stock trans mounts. After I get the exhaust routed I will make a rear brace to the bumper mounts for extra support.
Can you expand on how you see that more stress is transmitted to the rotor housing? If the stock dowels serve the purpose of preventing movement between the side and rotor housing all I have done is added more dowel cross sectional area which will spread out and reduce the shear stress on the stock dowel area. My dowels are 9/16" (0.563") diameter which is not small in my opinion (I think I have a typo in one spot that says 5/16"), the stock ones are 16mm (0.630) Mine are also press fit so they have a better ability to transmit force without deforming the base materials. Any larger and I would be compromising the wall thickness that supports the dowel in the rotor housing. Please input and ideas are much appreciated and thanks for the compliments.

patman

iTrader: (3)

I retract my comment.

Just FYI tho, i dunno what type of engineering you are studying (ME here), but if its anything structural at some point you will run into bearing stress on joints. Basically the idea is that if you have a small diameter pin holding a large force, the cross section of the pin may be large enough to take the stress no problem, but the interference area between the pin and the part may not be large enough to handle it, especially if the part is a weaker material like aluminum, and a crack will form, eventually leading to failure.

It took me a little while to figure out what it was about, but if you think about it it makes sense- the interference area is just the insertion length * the diameter, which can be pretty small, and even if there is lots of thickness on the part in that area, there will be a local concentration where the bearing stress exceeds the yield strength, and a crack will form.

That was a sucky explanation, but hopefully it makes some sense. Like I said, that was only a concern with the 5/16 pins I thought you were using, 9/16 should be no problem.

RXBeetle

Workin on the sparky BS. My formal ME education runs out with Phys I and Statics but I grew up in my dads tool and die shop dragging a wooden crate around so I could reach the handles.
I'm pickin up what you are saying though about pin diameter. If the pin were small it would it would cause a high enough stress on a small area to fracture the aluminum before an unmolested stock motor would be damaged under the same conditions.

What the basic formulas fail to consider is fit. A slip fit allows the pin to rack to some extent especially in hot aluminum. Now you are focusing the concentration of force to the perimeter of the hole, not evenly along the insertion length. It's a lever at that point. The side housing was the weak link from what I have seen on the forums and you can only get so much insertion into the iron so fit and pin diameter are the only way gain strength in the joint.

patman

iTrader: (3)

The side housing is only the weak link because the insertion area is smaller. the rotorhousing is much weaker, but the stock dowels distribute the stress over a much greater area than they do in the iron. think about it- the dowel passes through 3" of rotorhousing, but is only anchored half an inch on each side in the irons. As far as the pin twisting and applying a torque to break the iron, remember that the stock pin goes all the way through, so it will stay relatively square, whereas your shorter pin will be able to twist and do as you mentioned, which is not a comforting thought...

not by any means saying that your setup wont work, just throwing that out there. I personally am going to be studding my engine, but then I am shooting for 900bhp from the 3 rotor.