4-Rotor FB Build (side ports!!)
02-18-12, 09:45 PM
#128
Setting end play...
Your usual thrust assembly has pices with various thicknesses due to the manufacturing process. It's your job to find the right combo of parts to get .002". However the usual thrust pieces end up making the stack too thick due to a minor machining error on the front slip-on journal. It's only about 1mm too long. No biggie, but when you're talking in the thousandths of an inch, it's too much.
The shaft only has .016" to .017" free end play. It used to be zero until I clearanced the front stat bearing. I can work within this narrow window, I think.
Yes, it's fully seated against the taper. I impacted it on like a 20B.
So the journal realy is slightly too long. Right. I've never done this before so I'm discovering it as I go.
I asked Jantore if his 13B based 4 rotor had these problems. Nope. Hmm, gotta be a 12A issue.
A regular small thrust plate is 3.00mm usually. This is the one that rides up next to the shaft. It has a taper on one side to fit the shoulder where it expands at the stat bearing journal. This taper isn't necessary on the 4 rotor as it's a straight 90 degree there.
This means I can simply precision grind down the tapered side and not have to worry about it reducing the taper. About 2.00mm is what I'm looking for in the end.
I tested this theory with a slightly worn one. I rough ground it down to 2.04 to 1.98mm. A little too short but a step in the right direction.
Your usual thrust assembly has pices with various thicknesses due to the manufacturing process. It's your job to find the right combo of parts to get .002". However the usual thrust pieces end up making the stack too thick due to a minor machining error on the front slip-on journal. It's only about 1mm too long. No biggie, but when you're talking in the thousandths of an inch, it's too much.
The shaft only has .016" to .017" free end play. It used to be zero until I clearanced the front stat bearing. I can work within this narrow window, I think.
Yes, it's fully seated against the taper. I impacted it on like a 20B.
So the journal realy is slightly too long. Right. I've never done this before so I'm discovering it as I go.I asked Jantore if his 13B based 4 rotor had these problems. Nope. Hmm, gotta be a 12A issue.
A regular small thrust plate is 3.00mm usually. This is the one that rides up next to the shaft. It has a taper on one side to fit the shoulder where it expands at the stat bearing journal. This taper isn't necessary on the 4 rotor as it's a straight 90 degree there.
This means I can simply precision grind down the tapered side and not have to worry about it reducing the taper. About 2.00mm is what I'm looking for in the end.
I tested this theory with a slightly worn one. I rough ground it down to 2.04 to 1.98mm. A little too short but a step in the right direction.
02-19-12, 02:34 AM
#129
It's sitting at .003"! Pretty good, but I could go for .002". Then again, this is a chromoly shaft and will probably act differently than a stock one as it expands while warming up. I don't want to run out of clearance at the rear stat gear if it grows quicker than the engine.
From earlier when I determined I had .016" to .017" of end play to work with, I set out to get my .002" right in the middle for safety purposes. Well, after fiddling with it for more hours than I'd like to count, I ended up at almost exactly the half way point.
At first it was pulling the shaft too far forward and butting up against the stat bearing again, so I swapped in something with much less clearance and over-tighened the front stack so I could crank the engine and "machine" the softer stat gear and bearing material using the much harder shaft like a lathe.
It worked! After I got done and swapped the regular thrust stuff back in, I was able to measure .008" between the big thrust plate and the flat area of the stat gear where the thrust plate bolts to. I didn't have this kind of clearance before.
I popped the stat gear out and looked at it. Sure enough, the harder shaft had smoothed down any high spots in the stat gear bevel, leaving some metal bits behind. The shaft had a little clean spot in the oil where it had rubbed hard against the stat gear, but no other markings of any kind. Interesting (to me at least).
So I went ahead and put the whole thrust assembly back together and checked end play. It didn't seem to have any anymore so I swapped in a slightly thinner small thrust washer (the one that rides against the front counterweight). That gave me the .003" I mentioned earlier. Good enough for tonight.
I'd like some opinions on what end play to use on a 4 rotor. Thanks.
From earlier when I determined I had .016" to .017" of end play to work with, I set out to get my .002" right in the middle for safety purposes. Well, after fiddling with it for more hours than I'd like to count, I ended up at almost exactly the half way point.
At first it was pulling the shaft too far forward and butting up against the stat bearing again, so I swapped in something with much less clearance and over-tighened the front stack so I could crank the engine and "machine" the softer stat gear and bearing material using the much harder shaft like a lathe.
It worked! After I got done and swapped the regular thrust stuff back in, I was able to measure .008" between the big thrust plate and the flat area of the stat gear where the thrust plate bolts to. I didn't have this kind of clearance before.
I popped the stat gear out and looked at it. Sure enough, the harder shaft had smoothed down any high spots in the stat gear bevel, leaving some metal bits behind. The shaft had a little clean spot in the oil where it had rubbed hard against the stat gear, but no other markings of any kind. Interesting (to me at least).
So I went ahead and put the whole thrust assembly back together and checked end play. It didn't seem to have any anymore so I swapped in a slightly thinner small thrust washer (the one that rides against the front counterweight). That gave me the .003" I mentioned earlier. Good enough for tonight.
I'd like some opinions on what end play to use on a 4 rotor. Thanks.
02-19-12, 12:47 PM
#130
My first instinct would be to use double the stock clearance, assuming that twice the rotating length would result in twice the thermal expansion... but I don't know the difference in thermal coefficients involved.
Slightly too much would probably be better than slightly too little. The only build error I've ever made was cutting end play too fine; engine died of overheat in less than 10k miles
Slightly too much would probably be better than slightly too little. The only build error I've ever made was cutting end play too fine; engine died of overheat in less than 10k miles
02-19-12, 12:52 PM
#131
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My first instinct would be to use double the stock clearance, assuming that twice the rotating length would result in twice the thermal expansion... but I don't know the difference in thermal coefficients involved.
Slightly too much would probably be better than slightly too little. The only build error I've ever made was cutting end play too fine; engine died of overheat in less than 10k miles
Slightly too much would probably be better than slightly too little. The only build error I've ever made was cutting end play too fine; engine died of overheat in less than 10k miles
02-19-12, 03:08 PM
#133
Senior Member
i love this build, mainly because it looks like a normal person could piece this thing together after buying a kit. it would be so awesome seeing a old school fb on some nice old equips with that engine under the hood ! color scheme is awesome btw digging it.
02-20-12, 09:51 PM
#135
Jeff! Awesome work man. Can't wait to get back to see this in person.
I think the mounting thing would be the easiest part. If you cut the crossmember and add bent mild steel bars going from side to side it will be perfect. Thats how vanishing point racecars does it. They still say the setups are street legal too.
I think the mounting thing would be the easiest part. If you cut the crossmember and add bent mild steel bars going from side to side it will be perfect. Thats how vanishing point racecars does it. They still say the setups are street legal too.
02-23-12, 12:57 AM
#137
I have to take a break from the 4 rotor to "pay the bills" but now I can get a hardened oil pump. I also found a really nice front cover in the pile today. It has an older OMP with the adjustable stop. This is perfect for getting some pre-load on the OMP output; to "jack it open" so to speak. This lets me use a stock rod.
I'm thinking about clocking the OMP lever a little further open as another option. Or shorten the lever so it opens more per throttle open angle than stock.
Thoughts?
Remember it has to feed two engines worth of apex seals now. Premix will probably always be necesseary, but on those occasions when the mixture isn't quite right, the OMP has to take up the slack.
I'm thinking about clocking the OMP lever a little further open as another option. Or shorten the lever so it opens more per throttle open angle than stock.
Thoughts?
Remember it has to feed two engines worth of apex seals now. Premix will probably always be necesseary, but on those occasions when the mixture isn't quite right, the OMP has to take up the slack.
02-23-12, 09:53 AM
#139
At a given RPM with double the number of firing chambers, fuel consumption of your beast will be roughly double what the OMP was calibrated for by the factory.
Premix, being volumetric based on ratio of oil to fuel, is the safe solution.
02-23-12, 09:10 PM
#140
35r 13b first gen
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wire it all the way open haha i did this on my 12a streetport sidedraft... it smoked so badly... i think i had to fill up the oil everytime i got gas... never had to change it though... just the filter... everyone thought my car was about to blow up... worked great.... i know you probably want something more precise that this though...
haha i did this on my 12a streetport sidedraft... it smoked so badly... i think i had to fill up the oil everytime i got gas... never had to change it though... just the filter... everyone thought my car was about to blow up... worked great.... i know you probably want something more precise that this though...
03-15-12, 10:11 PM
#143
Bit of an update...
Starting to look into exhaust systems. So far I've narrowed it to two choices.
Choice 1:
something resembling the RB "streetport" exhaust where each 180 degree rotor pair is collected into a 2.5" secondary pipe, for two running side by side under the chassis as a "long secondary system"; each with its own presilencer acting like two short primary systems side by side. Then collect up over the rearend and into one big muffler in the stock rear location. I was going to test this type of setup on a regular RB streetport center section and powerpulse muffler for sound quality and noise control. If decent, it'll come out and get replaced with 2.5" components and a 2.5" or 3" main muffler.*
*main muffler size would depend on flow calculations and sound/noise considerations.
Choice 2:
collect both 180 degree rotor pairs early into dual 2.5", then travel for 6", then collect both into a single 3" as a "short primary/short secondary system" and pack the center section with mufflers. This option is lighter and may flow better because the theory is once the primaries collect into secondaries, there is nothing else to be gained flow-wise -- only losses can occour. A bit of a trade off weight-wise and flow-wise compared with the short primary/long secondary above, as I'm sure rotarygod would agree. But which is best? Perhaps the one the exhaust fabricator (myself) prefers?
Better include option 3:
long primary system with four 2" thickwall pipes, four presilencers, collect 80 to 100 inches from the engine into two sets of 2.5" collectors. Then exit through dual 2.5" mufflers. Or collect into 2.75" or 3" and then into a single 3" or 2.5" muffler, depending on noise and flow (and because 2.75" mufflers aren't common). But of course there isn't enough room for four presilencers under a 1st gen.
Starting to look into exhaust systems. So far I've narrowed it to two choices.
Choice 1:
something resembling the RB "streetport" exhaust where each 180 degree rotor pair is collected into a 2.5" secondary pipe, for two running side by side under the chassis as a "long secondary system"; each with its own presilencer acting like two short primary systems side by side. Then collect up over the rearend and into one big muffler in the stock rear location. I was going to test this type of setup on a regular RB streetport center section and powerpulse muffler for sound quality and noise control. If decent, it'll come out and get replaced with 2.5" components and a 2.5" or 3" main muffler.*
*main muffler size would depend on flow calculations and sound/noise considerations.
Choice 2:
collect both 180 degree rotor pairs early into dual 2.5", then travel for 6", then collect both into a single 3" as a "short primary/short secondary system" and pack the center section with mufflers. This option is lighter and may flow better because the theory is once the primaries collect into secondaries, there is nothing else to be gained flow-wise -- only losses can occour. A bit of a trade off weight-wise and flow-wise compared with the short primary/long secondary above, as I'm sure rotarygod would agree. But which is best? Perhaps the one the exhaust fabricator (myself) prefers?
Better include option 3:
long primary system with four 2" thickwall pipes, four presilencers, collect 80 to 100 inches from the engine into two sets of 2.5" collectors. Then exit through dual 2.5" mufflers. Or collect into 2.75" or 3" and then into a single 3" or 2.5" muffler, depending on noise and flow (and because 2.75" mufflers aren't common). But of course there isn't enough room for four presilencers under a 1st gen.
03-19-12, 12:35 AM
#145
Thinking about exhaust options a bit more. I'm starting to think the long secondary system described above (choice 1) with its 2.5" presilencers is a bad idea. Why? Because once you collect the primaries, the important exhaust tuning is done. So while it can work because it's based on two regular collected headers, it just adds unnecessary weight, complexity and cost (two 2.5" presilencers aren't cheap) and adds no power advantages. So scrap option one. I'd only try it if I had an RB "streetport" center section available and wasn't gonna keep the 4 rotor in the car for very long, as the powerpulse muffler was designed for dual primaries which are loud, not dual secondaries which are quiet(er). I wanna hear the 4 rotor. Plus it's kinda restrictive.
So it looks like option 2 is the one I'll do.
So it looks like option 2 is the one I'll do.
03-19-12, 02:13 AM
#147
Ah, you got the Contra reference! I still recall reading that in Nintendo Power magazine one Sunday morning back then. I committed it to memory as I'm sure thousands of kids did.
I just think it's cool how the shaft has the same configuration.
I have a small update on the exhaust situation. Turns out the RB streetport is available so that's what I'll use.
There's something anticlimactic about this so it must be the right choice. Actually it's because the 4 rotor won't stay in the car for very long. Just long enough to test and make sure it will run. Then a 13B will go in so someone can drive it.
I just think it's cool how the shaft has the same configuration.
I have a small update on the exhaust situation. Turns out the RB streetport is available so that's what I'll use.
There's something anticlimactic about this so it must be the right choice. Actually it's because the 4 rotor won't stay in the car for very long. Just long enough to test and make sure it will run. Then a 13B will go in so someone can drive it.
03-29-12, 03:00 PM
#149
Tiny update:
The stat gears in the end plates need to be shortened a little. This will give back the end play I'm lacking right now. Seems Jeff Bruce may have made the slip-on journals about 1mm too long, so I'll shorten the stat gears by that much. It'll gain me about 2mm of end play while not weakening the stat gears.
No telling when I'll do this, but figured I'd spread the word. I know you guys like updates in any form.
The stat gears in the end plates need to be shortened a little. This will give back the end play I'm lacking right now. Seems Jeff Bruce may have made the slip-on journals about 1mm too long, so I'll shorten the stat gears by that much. It'll gain me about 2mm of end play while not weakening the stat gears.
No telling when I'll do this, but figured I'd spread the word. I know you guys like updates in any form.
& it also does a great job of blowing all the leaves out of the gutters.