flywheel too big for tranny??
01-02-13, 07:39 AM
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flywheel too big for tranny??
I need some help guys. I have a stock 12A in my Spitfire (RotoSpit) that I am swapping out to a ported 12A. I went to go drop the motor in and realized that the new motor with an aftermarket flywheel is too large to fit in the bellhousing-it hits two of the raised areas around the bolt holes. The old stock flywheel was 11 5/8" across from tooth to tooth while the new one is 12 1/2". I can grind down these two areas (no bolts go there anyway on the new engine) but I am concerned that the starter will not engage properly and it will be hitting in about 1/2" too far. Can I use this flywheel and just buy a different starter or do I need a new flywheel?. PICS BELOW-Thanks Rich
Last edited by spitfun; 01-02-13 at 07:44 AM.
01-02-13, 12:09 PM
#5
You need to change something.
I also noticed the alignment dowel is stuck in your tranny (upper corner of the bellhousing). But someone ground it down on your new engine. See if you can pull it from the tranny and swap it in your new engine. Be sure to remove the old half ground away one first. Otherswise it won't just be a flywheel keeping the engine from mating up with the bellhousing.
Hopefully having two broken threaded holes and a missing dowel won't cause you too many headaches. At least swap the dowel over.
And a word of advice. Don't post one-liners in a bunch of threads just to raise your post count. Thanks.
I also noticed the alignment dowel is stuck in your tranny (upper corner of the bellhousing). But someone ground it down on your new engine. See if you can pull it from the tranny and swap it in your new engine. Be sure to remove the old half ground away one first. Otherswise it won't just be a flywheel keeping the engine from mating up with the bellhousing.
Hopefully having two broken threaded holes and a missing dowel won't cause you too many headaches. At least swap the dowel over.
And a word of advice. Don't post one-liners in a bunch of threads just to raise your post count. Thanks.
01-02-13, 12:35 PM
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So,what do I do here guys. what can I keep and what do I have to change? Sorry about the one-liners-when I posted somewhere else it was only 10 posts needed,when I went here it was now 20! Rich
01-02-13, 12:46 PM
#7
Do you have a way to remove the alignment dowel from the tranny? Do you have a way to remove the remnant from the engine?
You haven't told us the new engine's specs yet. What year rotating assembly does it have? If it matches your old engine, you can simply swap the flywheel and clutch stuff over. Easy. If you have a 54mm socket, that is.
You haven't told us the new engine's specs yet. What year rotating assembly does it have? If it matches your old engine, you can simply swap the flywheel and clutch stuff over. Easy. If you have a 54mm socket, that is.
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01-02-13, 01:20 PM
#8
One word of advice. You DO NOT need a twin disc in a tiny car like a spitfire. Twin discs are able to hold more torque than a single with reduced pedal effort. You're not running a turbo are you? Then there's no need for such a high strung disc on an NA. Infact a stock duty clutch setup feels like a street strip setup in an MG Midget/Sprite. Your spitfire isn't much bigger.
Another piece of advice I can give is from personal experience. I have a rotary MG Midget. I tried it once with a stock 30 pound flywheel. It was too heavy for the chassis and could burn out easily at 2k rpm. Then I swapped to a Racing Beat light steel flywheel in 225mm. This was a major improvement. Then when I built the new engine for it, I decided to go RB aluminum. Now I'm having second thoughts based on how well it drove on the light steel. Earlier I asked you about the year of your rotating assembly. This is important not only for whether you use your stock 26 pound flywheel seen above, but the weight of the rotors themselves can play a role in how it drives in a tiny car. My first 13B in my MG had old R5 rotors and a REPU flywheel as it was out of my rotary truck for test running purposes. The stock 30 pound flywheel was kinda ok in the REPU, but too much for the MG. Then when I tested the light steel flywheel, it was perfect in the MG but too light for the REPU. See where I'm going with this? Anyway the new engine I just built for the MG has S4 NA rotors. These weigh less than old R5 rotors. So if I were to combine these lighter rotors with an even lighter flywheel, it might turn out too light for the MG. Again I felt that the old setup with the heavy R5 rotors and the RB light steel flywheel was a great combination in the MG. So I've decided to yank the engine out of the MG and swap from the aluminum to the light steel this winter. But while it's out, I might just break it in fully in my REPU. Might as well as the weather is too cold and nasty to work on a full new engine build for the REPU, but a simple engine swap takes only a couple of hours over a couple of days. And if I go through with this idea, I'm definitely swapping to an S4 NA flywheel for the time it's going to be in the REPU. Does this all make sense? I don't know you and I have no idea how much you've ever messed with flywheels or even thought about it before. Maybe I'll convince you to go with a light steel flywheel in your spitfire huh?
Or aluminum if you really need the reduced inertia on your streetport, which I doubt. Streetports lose low end torque you know. Good to keep some mass when you port. By the way my MG's new engine is streetported and it's only getting a stock duty disc and pressure plate in 225mm but I might swap down to 215mm as the chassis is so light 225mm isn't needed.
Also what rear diff gearing do you have? My MG's is super tall from a '79 freeway flier. Again a reason to keep a little mass in the flywheel. I might swap to a 1st gen RX-7 rear end some day, but first things first = engine.
Flywheel weights for quick reference:
REPU and old school '80 and older 12A and 13B = 30 pounds
81-82 12A only = 23 pounds
83-85 12A = 26 pounds
GSL-SE 13B = 26 pounds
S4 NA 13B = 24 pounds
RB light steel = 13 pounds
RB aluminum = 7.5 pounds
the rear counterweight = 4 pounds (so add this to your aftermarket flywheel for total weight)
Another piece of advice I can give is from personal experience. I have a rotary MG Midget. I tried it once with a stock 30 pound flywheel. It was too heavy for the chassis and could burn out easily at 2k rpm. Then I swapped to a Racing Beat light steel flywheel in 225mm. This was a major improvement. Then when I built the new engine for it, I decided to go RB aluminum. Now I'm having second thoughts based on how well it drove on the light steel. Earlier I asked you about the year of your rotating assembly. This is important not only for whether you use your stock 26 pound flywheel seen above, but the weight of the rotors themselves can play a role in how it drives in a tiny car. My first 13B in my MG had old R5 rotors and a REPU flywheel as it was out of my rotary truck for test running purposes. The stock 30 pound flywheel was kinda ok in the REPU, but too much for the MG. Then when I tested the light steel flywheel, it was perfect in the MG but too light for the REPU. See where I'm going with this? Anyway the new engine I just built for the MG has S4 NA rotors. These weigh less than old R5 rotors. So if I were to combine these lighter rotors with an even lighter flywheel, it might turn out too light for the MG. Again I felt that the old setup with the heavy R5 rotors and the RB light steel flywheel was a great combination in the MG. So I've decided to yank the engine out of the MG and swap from the aluminum to the light steel this winter. But while it's out, I might just break it in fully in my REPU. Might as well as the weather is too cold and nasty to work on a full new engine build for the REPU, but a simple engine swap takes only a couple of hours over a couple of days. And if I go through with this idea, I'm definitely swapping to an S4 NA flywheel for the time it's going to be in the REPU. Does this all make sense? I don't know you and I have no idea how much you've ever messed with flywheels or even thought about it before. Maybe I'll convince you to go with a light steel flywheel in your spitfire huh?
Or aluminum if you really need the reduced inertia on your streetport, which I doubt. Streetports lose low end torque you know. Good to keep some mass when you port. By the way my MG's new engine is streetported and it's only getting a stock duty disc and pressure plate in 225mm but I might swap down to 215mm as the chassis is so light 225mm isn't needed.Also what rear diff gearing do you have? My MG's is super tall from a '79 freeway flier. Again a reason to keep a little mass in the flywheel. I might swap to a 1st gen RX-7 rear end some day, but first things first = engine.
Flywheel weights for quick reference:
REPU and old school '80 and older 12A and 13B = 30 pounds
81-82 12A only = 23 pounds
83-85 12A = 26 pounds
GSL-SE 13B = 26 pounds
S4 NA 13B = 24 pounds
RB light steel = 13 pounds
RB aluminum = 7.5 pounds
the rear counterweight = 4 pounds (so add this to your aftermarket flywheel for total weight)
01-02-13, 08:49 PM
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Ok, I am still new to these rotaries and have a few questions. From what I've read I believe I can use the stock steel flywheel off the old motor as long as I use the counter weight from the new streetported motor with no ill effects, correct? This is an autocross car,do you guys suggest using the stock flywheel (I have the 26 lb. 83-85 on the old motor) or should I go with a lighter flywheel to allow the motor to rev up quicker? Thanks for the time Rich
01-02-13, 10:17 PM
#10
There are a few things about rotaries I like. In this case it's clutch and flywheel stuff. So I don't mind spending a little time typing about it.
You have a stock iron flywheel and it will only work if the new engine rotors are also 83-85. Do you know what year they are? One way to find out is take off the aftermarket flywheel and look at the counterweight. If it has a little circle around the nut, it's an 83-85.
If you'd like something that revs up quicker, you could look for a light aftermarket flywheel like the two Racing Beat options I mentioned before. There are some others like grddy 8 pound steel and maybe ACT makes one for NAs, not sure. The good thing about your setup is you already have the rear counterweight. Then you could swap your old disc and pressure plate over. Measure the disc thickness. It should be 8mm.
You have a stock iron flywheel and it will only work if the new engine rotors are also 83-85. Do you know what year they are? One way to find out is take off the aftermarket flywheel and look at the counterweight. If it has a little circle around the nut, it's an 83-85.
If you'd like something that revs up quicker, you could look for a light aftermarket flywheel like the two Racing Beat options I mentioned before. There are some others like grddy 8 pound steel and maybe ACT makes one for NAs, not sure. The good thing about your setup is you already have the rear counterweight. Then you could swap your old disc and pressure plate over. Measure the disc thickness. It should be 8mm.
