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Hey all,
have been having some huge issues with a motor i'm building... have rebuilt it 2x now and have had the same problem both times.. Problem is that the rear rotor gear land is somehow coming into contact with the rear plate and chewing the **** out of it, hence making the oil control rings ineffective making a hidiously smokey motor and damaging the plate, i've had it machined once already.. and am going to have to do it again... Motor had a meticulous rebuild, all bearings replaced, everything spec'd out...but still this problem occurs... any thoughts on what could be causing this to happen? I first though that maybe the rotor gear itself had walked out, but no, no i checked that and its within tolerance. |
so u have specced clearance of over 0.08mm from rotor edge to gear land and sufficient clearance from rotor to end plate? have u measured it with a descent micrometer?
do u have descent side seal clearance? they arent forcing themselves against the plate when hot? have u got pics? |
Originally Posted by butcheryboy' post='912402' date='Nov 25 2008, 02:00 AM
Hey all,
have been having some huge issues with a motor i'm building... have rebuilt it 2x now and have had the same problem both times.. Problem is that the rear rotor gear land is somehow coming into contact with the rear plate and chewing the **** out of it, hence making the oil control rings ineffective making a hidiously smokey motor and damaging the plate, i've had it machined once already.. and am going to have to do it again... Motor had a meticulous rebuild, all bearings replaced, everything spec'd out...but still this problem occurs... any thoughts on what could be causing this to happen? I first though that maybe the rotor gear itself had walked out, but no, no i checked that and its within tolerance. A common outcome from overheated oil and or, coolant. you can also do it by just missing a shift and screaming the engine. So a rev limiter is a good insurance policy. The gear walks out a bit and the show is over. Anytime you have a rotor out of an engine, slip it in the press and give it a good push. 9 times out of 10 it will move a bit. That is why there is a snap ring option from Racing Beat and others. You can also drill and tap 6 little holes and screw in socket head set screws that engage the gear and the rotor, after you have pushed it in good and hard. I grind the gear land and the opposite land down to the minimum height. You might also check the oil spray hole and nozzles for a partial blockage. A crank from an older car can collect a lot of debris and varnish internally like a centrifugal separator. You might also check the rotor bearing surface on the crank for a tiny amount of taper. Generally the nitride is only .003" deep in the iron, and one lapping is about it. There is only a need for nitride for long wear life. So be sure to have the iron redone, or just start again with a new iron. |
This motor has only been started up a few times and run for only a few minutes before the problem became obvious again. So no over heating of the oil or coolent eaither. Oil sprayers and nozzels have all been checked and blown out with compressed air. I went kinda OCD when doing this build...
Will check the shaft again, but I didnt see detect any taper on the shaft bearing surfaces initially... All other clearances are perfect, all other parts of the motor are undamaged, except for the rear plate which makes the culprit the rear rotor. When i tore it down the first time, you could see bits of cast iron from the plate stuck to the gear land. Guess ill be ripping it down again and as you say Lynn, chucking both rotors in the press and then grinding down the lands to the mininum height. Then get the plate machined again... any other tips regarding this problem?...motor is a 12a Bridgeport Rx3 block with original RX3 rotors. Cheers |
Originally Posted by butcheryboy' post='912427' date='Nov 25 2008, 10:50 AM
This motor has only been started up a few times and run for only a few minutes before the problem became obvious again. So no over heating of the oil or coolent eaither. Oil sprayers and nozzels have all been checked and blown out with compressed air. I went kinda OCD when doing this build...
Will check the shaft again, but I didnt see detect any taper on the shaft bearing surfaces initially... All other clearances are perfect, all other parts of the motor are undamaged, except for the rear plate which makes the culprit the rear rotor. When i tore it down the first time, you could see bits of cast iron from the plate stuck to the gear land. Guess ill be ripping it down again and as you say Lynn, chucking both rotors in the press and then grinding down the lands to the mininum height. Then get the plate machined again... any other tips regarding this problem?...motor is a 12a Bridgeport Rx3 block with original RX3 rotors. Cheers If the rotor still looks good. Measure it with a height gage or calipers and find the thickness in three places, just below the corner seal holes. Then with a straight edge masure the height of the land area to that same place below the corner seal hole. My bet is the gear is out a bit. There is no other explaination. Perhaps debris is between the gear and the rotor now. For a failure to take place at idle just screams that a fault was in place before assembly. It is OK to touch the lands against the irons now and then, usually under very hard braking, or upshifting a dog ring trans. But the black death seen in so many cases is just plain old "rotor too thick for the space" problem. The steel gear against the iron is just not a good bearing match. A shorter land and 6 Teflon buttons would be way better, but the lands just about never touch. The springs in the side seals, corner seals and oil scrapers do a great job keeping the rotor centered between the irons. If you were planning on shifting above 9,000 RPM, then the rotor should be shaved down about .010" on each side from the outer oil scraper groove. For over 10,000 RPM then I would go .012". Bearings should have .0035" to .0040" clearance. Lynn E. Hanover |
Originally Posted by Lynn E. Hanover' post='912495' date='Nov 27 2008, 02:11 AM
If the rotor still looks good. Measure it with a height gage or calipers and find the thickness in three places, just below the corner seal holes. Then with a straight edge masure the height of the land area to that same place below the corner seal hole.
My bet is the gear is out a bit. There is no other explaination. Perhaps debris is between the gear and the rotor now. For a failure to take place at idle just screams that a fault was in place before assembly. It is OK to touch the lands against the irons now and then, usually under very hard braking, or upshifting a dog ring trans. But the black death seen in so many cases is just plain old "rotor too thick for the space" problem. The steel gear against the iron is just not a good bearing match. A shorter land and 6 Teflon buttons would be way better, but the lands just about never touch. The springs in the side seals, corner seals and oil scrapers do a great job keeping the rotor centered between the irons. If you were planning on shifting above 9,000 RPM, then the rotor should be shaved down about .010" on each side from the outer oil scraper groove. For over 10,000 RPM then I would go .012". Bearings should have .0035" to .0040" clearance. Lynn E. Hanover Cheers Lynn, legend. |
Originally Posted by butcheryboy' post='912508' date='Nov 27 2008, 07:51 AM
Cheers Lynn, legend.
Just a quick question...as per rx3 FSM, torque specs for through bolts on Rx3 blocks (12a) is 24 ft/lbs... how critical is this and could an over tourqued motor cause this chewing of the rear plate...? say 30 ft/lbs? Have had the plate machined and have pressed the rotors in the press, and are just about to re-assemble the block when i got thinking... Also how common is it for rotor housings to shrink/warp? as im thinking that a slightly thinner rear housing would cause the gear land to run closer to the plate surface, and when heated, may expand and touch. |
It can happen, usually the chrome gets flaked all to hell when it happens though. Did you measure the rotor housings?
The heat expansion is not going to be really high, if anything the aluminum will try to expand more, within the constraints of the tension bolts. Get the engine hot enough and the tension bolts will win and the aluminum will crush. I am kind of a nut, I slightly undertorque my engines. The last 13B I did, I think I torqued to 22ft-lb. The benefit is that I haven't hurt the rotor housings from overheating, either. |
Originally Posted by heretic' post='913100' date='Dec 10 2008, 05:57 AM
It can happen, usually the chrome gets flaked all to hell when it happens though. Did you measure the rotor housings?
The heat expansion is not going to be really high, if anything the aluminum will try to expand more, within the constraints of the tension bolts. Get the engine hot enough and the tension bolts will win and the aluminum will crush. I am kind of a nut, I slightly undertorque my engines. The last 13B I did, I think I torqued to 22ft-lb. The benefit is that I haven't hurt the rotor housings from overheating, either. Housings both measured a clean 70mm in several places, tourqued the motor to 24ft/lbs and everything seems sweet. Guess will just have to wait and see on start up. |
if the rotor housings measured 70mm what did the rotors measure?
the housings do shrink a bit, the thrichoid surface sags in the middle. at 70mm it sounds like they are good though i dont really trust my torque wrench, so i shoot for the center of the range, which is more like 25lbs/ft i have done a studded motor, and torqued it up to 55lbs/ft with no issues other than the owner, run an air filter. |
Originally Posted by j9fd3s' post='913107' date='Dec 10 2008, 07:57 AM
if the rotor housings measured 70mm what did the rotors measure?
the housings do shrink a bit, the thrichoid surface sags in the middle. at 70mm it sounds like they are good though i dont really trust my torque wrench, so i shoot for the center of the range, which is more like 25lbs/ft i have done a studded motor, and torqued it up to 55lbs/ft with no issues other than the owner, run an air filter. Rotors both measured 69.85mm at the thickest point, with side plate clearance of 0.08 rear rotor and 0.09 front rotor..pretty much factory specs. |
Originally Posted by butcheryboy' post='913126' date='Dec 10 2008, 12:55 PM
Rotors both measured 69.85mm at the thickest point, with land to rotor clearance of 0.08 on the rear rotor and 0.09 on the front rotor..pretty much factory specs.
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*Correction* Land clearance of 0.08 on the rear rotor and 0.09 on the front rotor..pretty much factory specs otherwise.
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Originally Posted by butcheryboy' post='913156' date='Dec 10 2008, 10:32 AM
*Correction* Land clearance of 0.08 on the rear rotor and 0.09 on the front rotor..pretty much factory specs otherwise.
sounds like its a runner then.... |
Originally Posted by j9fd3s' post='913158' date='Dec 11 2008, 06:34 AM
sounds like its a runner then....
She's a runner https://www.nopistons.com/forums/pub...IR#>/smile.gif |
Re: Rotor Gear Land Chewing Rear Plate to Pieces...WHY?
Figure this might be the best place to put this!
ive been rummaging about everywhere to find an answer to my woes, bearly got any bloody hair left ive been scratching my head in deep thought over this for long. Ive built a few engines over here on this side of the pond and love it :-) im in the process off getting my 1st half bridgey (MSP) together for a friend of mine, ports are cut and the housings went off for surface grinding, 3 thou taken off all 4 faces and they came out amazingly flat :eek5: 30 mins of hand lapping using 600 grit valve grinding past has left us with a very nice dul srface with a rating of about 9 - 11 RA. good stuff, all seems set to go! BUT and its a big BUT since i did this ive encountered problems with 4 other engines ( not mine the bridgey was the 1st to be lapped of mine) that have had surface treatments 3 lapped and 1 surface ground. the 1st time i noticed a problem i had an engine shipped to me to use as parts, when it arrived it had been painted, so obviously not a factory build. upon strip down it looked like it had been built with a granade inside :eek5: exept the housings are in remarkably good nick. the iron on the other hand were severly scored and the areas were the rotor gear runs is blue with heat and got some pretty but nasty patterns going on. the front rotor is in good nick although the front iron is chewed up to hell. the rear rotors gear is mangled unbelevably bad and the iron its self looks like its been half digested and spat back out. after a bit of brake cleaner it became clear that the irons had been surface ground as the grinding marks were still there over the whole surface of the irons. so i measured them up against stock irons and the rear iron is short by 6 thou the front 7 thou and the center iron a full 13 thou (6.5 a side im guessing) this is blatantly too much removed and explains the rouble with the large steps on the housings from wear as there is no nitride treat areas left :nono:i cannot understand however why this would cause the rotors to touch the housing the next time i saw it i was at a track day and friend from down south who built his own engine's car started smoking quite badly at idle, hed done a couple of thousand miles on the engine. when he built it he had the side walls lapped. i cannot remember the exact numbers but not much was removed, im quite sure this is the same problem again (and obviously the same problem the OP of this thread had) my 3rd contact with it was on an engine being run in an off road race buggy, the engine had been built quite recently by pip gardner who had given the plates a gental lapping before the rebuild .... i doubt he removed much material at all as the engine was an S2 engine that had done about 14k miles tops :eek5:... when i went to see the car it had been built just 200 miles and both rotors were nackard with VERY low compression although no signs of oil coming out of the plug holes on cranking it was a bit smokey again at low revs. Then just yesterday another of my southern mates rang me, he'd just finished running in a low power reni but needed to pop some new stationary gear bearings in it (he didnt have any on the build) before he could sell the car. when he went to take out the front gear nothing would get it to budge so he set in stripped the engine back down with the intention of finding out why, what he found was again a bit disturbing. both the front and rear side walls were showing wear, the front in particular. although you couldnt see any damage to the rotor gears the wear on teh side was definatly down to the gear touching it!!! here again he had had the plates lapped, and bearly removed any material at all. it was his test lapping engine if you like. he got kinda lucky that he stripped it down i guess :eek4: anyway so thats 4 engines, all have been lapped in some form or another and all are having problems with the gears touching the size housings!!! its worth noting also that me and james among many others (including the many real specialists in the states as you know) have had great success rebuilding renesis engines without having the side irons lapped PICS COMING SOON :D |
Re: Rotor Gear Land Chewing Rear Plate to Pieces...WHY?
Originally Posted by benedunn
(Post 853296)
Figure this might be the best place to put this!
ive been rummaging about everywhere to find an answer to my woes, bearly got any bloody hair left ive been scratching my head in deep thought over this for long. Ive built a few engines over here on this side of the pond and love it :-) im in the process off getting my 1st half bridgey (MSP) together for a friend of mine, ports are cut and the housings went off for surface grinding, 3 thou taken off all 4 faces and they came out amazingly flat :eek5: 30 mins of hand lapping using 600 grit valve grinding past has left us with a very nice dul srface with a rating of about 9 - 11 RA. good stuff, all seems set to go! BUT and its a big BUT since i did this ive encountered problems with 4 other engines ( not mine the bridgey was the 1st to be lapped of mine) that have had surface treatments 3 lapped and 1 surface ground. the 1st time i noticed a problem i had an engine shipped to me to use as parts, when it arrived it had been painted, so obviously not a factory build. upon strip down it looked like it had been built with a granade inside :eek5: exept the housings are in remarkably good nick. the iron on the other hand were severly scored and the areas were the rotor gear runs is blue with heat and got some pretty but nasty patterns going on. the front rotor is in good nick although the front iron is chewed up to hell. the rear rotors gear is mangled unbelevably bad and the iron its self looks like its been half digested and spat back out. after a bit of brake cleaner it became clear that the irons had been surface ground as the grinding marks were still there over the whole surface of the irons. so i measured them up against stock irons and the rear iron is short by 6 thou the front 7 thou and the center iron a full 13 thou (6.5 a side im guessing) this is blatantly too much removed and explains the rouble with the large steps on the housings from wear as there is no nitride treat areas left :nono:i cannot understand however why this would cause the rotors to touch the housing the next time i saw it i was at a track day and friend from down south who built his own engine's car started smoking quite badly at idle, hed done a couple of thousand miles on the engine. when he built it he had the side walls lapped. i cannot remember the exact numbers but not much was removed, im quite sure this is the same problem again (and obviously the same problem the OP of this thread had) my 3rd contact with it was on an engine being run in an off road race buggy, the engine had been built quite recently by pip gardner who had given the plates a gental lapping before the rebuild .... i doubt he removed much material at all as the engine was an S2 engine that had done about 14k miles tops :eek5:... when i went to see the car it had been built just 200 miles and both rotors were nackard with VERY low compression although no signs of oil coming out of the plug holes on cranking it was a bit smokey again at low revs. Then just yesterday another of my southern mates rang me, he'd just finished running in a low power reni but needed to pop some new stationary gear bearings in it (he didnt have any on the build) before he could sell the car. when he went to take out the front gear nothing would get it to budge so he set in stripped the engine back down with the intention of finding out why, what he found was again a bit disturbing. both the front and rear side walls were showing wear, the front in particular. although you couldnt see any damage to the rotor gears the wear on teh side was definatly down to the gear touching it!!! here again he had had the plates lapped, and bearly removed any material at all. it was his test lapping engine if you like. he got kinda lucky that he stripped it down i guess :eek4: anyway so thats 4 engines, all have been lapped in some form or another and all are having problems with the gears touching the size housings!!! its worth noting also that me and james among many others (including the many real specialists in the states as you know) have had great success rebuilding renesis engines without having the side irons lapped PICS COMING SOON :D Once you have ground the irons or, lapped extensively you are through the Nitride. Now the wear life will be shorter. A few years depending on the quality of your air filter and your top oil. A name brand SYNTHETIC 2 cycle oil in a premix at 1 ounce per gallon of fuel or using an OMP adaptor to feed the 2 cycle oil from a bottle on the firewall. Rotaries do not toleate dust or dirt in any size. So grease the gasket surfaces in you air cleaner so nothing gets through to the engine. Lynn E. Hanover |
Re: Rotor Gear Land Chewing Rear Plate to Pieces...WHY?
Lynn, I absolutely agree with your advice on greasing the air filter and using 2 stroke
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Re: Rotor Gear Land Chewing Rear Plate to Pieces...WHY?
sound advice indeed lyn ... and advice i adeer to religusly in my own car! thank you :D
i like the mod idea too!!! what im wondering is why these engines arnt having problems on the factory build, why they are ok if you dont touch the housings and why they suddenly all have problems when you do got me thinking tho, wonder if the finish is not good enough and its causing exesive friction and inturn heat build up which is causing the gear to move out as you say :confused: cheers for getting back to me anyway :thumbsup: |
Re: Rotor Gear Land Chewing Rear Plate to Pieces...WHY?
Or the nitriding process has been changed and is thinner than previously, remember we've had a bit of this issue with the '09 motor from the start - it had some marks already, although did a lot more than 200 bloody miles last time (although the actual failure was warped apex seals last time)
I'd be very surprised if it were dirt in the engine given the intake air is filtered twice through 3 filters, and the filters are sealed in, lubrication shouldn't be an issue given the amount of 2-stroke we run. Pity I don't still have access to the TiN coating plasma spray at WPS :D |
Re: Rotor Gear Land Chewing Rear Plate to Pieces...WHY?
chuffin hell phil!!! fancy you found this thread haha
IMO now im thinking the cast iron that the rx8 irons are made out of is simply cheap crap! i toold an iron down to the nitriding shop near me and they stuck it in the oven for 2 days for nowt to see what would happen ... they managed a nitride layer 14 thou deep but the faces didnt come out perfectly flat so a couple of thou would need grinding back off that! what was intresting (and i was gonna talk to you about this if youd ring me :-P) was that they were very suprised how un hard the finish was ... i didstinctly remeber numbers like 400 and 500 being used but will have to ring them tomorrow or tuesday to have another chat about it ... long story short they said there wasnt enough of what they needed in the iron to get a truerly untouchable finish and even the nitride layer was pretty soft!!! im now looking into other avenues we have a plasma spraying company that i already use to refurb stuff basically they spray industrial hard steel onto whatever suface you like and then grind it off to better than factory finish ... going on that 10a and early 12a were not nitide treated and relyed on the hardness of the metal itself i figure spraying on a completely new layer of supper tuff metal smothed off to within 13 RA could be viable alternative!! although it would require grinding 7 or so thou on spraying 10 thou back on and then grinding 3 thou back off so a couple of trips to the grinders both avenues are quite expensive ... nitriding would probably be the favorite in that respect but im unsure if i trust the irons after what ive seen now!!! thats 4 engines that have all done the same thing and the only thing in common is the grinding or lapping of the irons!!! back o what i was saying i think the tissue paper the MSP irons are made of rely completely on the nitride layer which is so thin you could see through it, just shows that they rushed manufacturing and forced costs down by skimping on material .... not surprising considering the price of the car tho :ohwell: |
Re: Rotor Gear Land Chewing Rear Plate to Pieces...WHY?
Well, you can make the nitriding harder on soft castings, but it means a thinner layer than usual - I reckon that's what Mazda have done perhaps. However, I think it was the debris from the warped rotor tips that did ours to start with - lesson there perhaps - don't touch the side housings, even if they're marked.
Wish I'd found out 'fore we lost the CNC mill, could have made some. |
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