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Post by mrmotors on Dec 31, 2019 20:32:11 GMT -6
I still feel, for what it's worth, that until you get a known accurate working tach for a Xenoah engine, stock or otherwise, and connect it to your engine and verify either one of your digital aftermarket units you could very well be going in circles. It very well could be the rabbit hole we all have gone down at times and can't see the woods for the trees... just sayin..It is still a question that needs answered to me...
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Post by midniterupper on Jan 1, 2020 7:37:58 GMT -6
Yeah, This one is a odd challenge for sure. Never ran into a situation like this before either but I'm sure we will get it figured out! Kinda weird that the lack of rpm's followed the clutch swap. Both pipes are clear, the silencer boxes are also. I'd like to play a bit today with the EGT gages installed to see what the temperature range is for both pipes. That would of course would help validate the jetting too. It would be nice to swap another set of functional carbs on it just to see, but then another dialed in primary would be helpful also.
One thing I noted while I was verifying the timing at 6000 rpm was that once the primary grabbed the belt at engagement (around 5300) but when the track really begins to wind up, the rpm's seemed to drop by 400 rpm consistently. I am probably not explaining this very well but it didn't seem to make sense to me. It's not a bog, just a drop of rpm. Could be just the added rotational resistance of the drive train beginning to spin, not sure.
Good question on the needle and seats, but they seem fine. No leakage of fuel in the cylinders when the motor sits for a while, checked and rechecked the float levels. Always starts easy. As we discussed earlier I believe they are not factory carbs from Rupp at all. They seem to do their job for now but we'll keep an eye on them.
I replaced the chaincase and driveshaft bearings as an attempt to ensure something wasn't wrong with them while I was in there. The idler bearings all seemed good as well. It's strange the rpm's climb so quickly without the drive belt on, 8400-8500 no problem. Install the belt, 7600 max. I'll probably end up doing the procedure of removing the drive chain, reinstalling everything to make the motor run and physically shift out both clutches to see the rpm pattern then. I do have a gut feeling that I need to play with grinding weights to come up with a custom profile and actual less weight in grams, maybe around 41 or 42 grams. Good thing I have some time to get ready.
Thanks again for your help and input! Happy New Year to All! 2020 is gonna be a Great Year for the Rupps!
BTW, What a great post. This community is the Best!
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Post by Ruppsforever on Jan 1, 2020 13:32:02 GMT -6
Are you sure you are winding that secondary right ?? I don't know exactly what you are using but you always have to twist against the spring to get to the next set of ramps to line up. I've seen people just throw secondary's together without twisting them before.
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Post by midniterupper on Jan 1, 2020 16:42:05 GMT -6
Yep, done that before! Right now on the reverse secondary I have the yellow spring, 53 degree helix set at 12 pounds preload. When the sled is on the stand, I can see both clutches shifting out nicely so I think we have the secondary assembled correctly.
I was able to get the sled out and play for quite a while today and got some more data to play with. First of all, the sled rocks! Engages now at 5400 rpm, still topping out at 7600 on the Koso. When the sled is at the 100' mark, it wakes up and goes! Incredible for a 440. The top end is still unknown at this point, I believe the track was expanding and began to ratchet on the drive cogs. Something made more racket down there at higher speeds at first then even when I did holeshots so I'll have to look around. I did back off the track tension quite a bit when I was fooling around with trying to reduce any drive friction. I'll tighten it up and try again tomorrow to see if the ratcheting goes away.
Another thing I was able to play with was the Koso gage. It displays and warns you if things exceed the programmed temps and it does record the highest exhaust temp also. Playing today with wide open runs, the highest temp recorded was 1153 degrees (PTO) and 1180 degrees (MAG). Wasn't sure if this is in the ball park for optimal temps for my main jetting. Plugs do appear a bit dark and oily but it runs so good. I imagine once we get the rpm's up there, it may run a little hotter?
I am also going to try increasing the clutch center to center distance just a tiny bit. Maybe the belt isn't truly bottoming out in the secondary and topping all the way on the primary, there is a little black marker left at the very top of the primary, so maybe....
Now that the sled is flying, I need some better brakes. I disassembled the original brake assembly, cleaned and polished all sliding surfaces and it seems to work but it doesn't slow down the sled enough. Do you guys recommend a different set up using hydraulics? I'd hate to earn the nickname of "Splat"!
Oh well, I'm having a ball! Until next time.....
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Post by mrrupp1 on Jan 2, 2020 12:10:23 GMT -6
Just a thought maybe try taking the mufflers off and see what kind if RPM you can get. Clint
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mutt
Senior Member
Posts: 36
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Post by mutt on Jan 2, 2020 13:49:36 GMT -6
Yep, done that before! Right now on the reverse secondary I have the yellow spring, 53 degree helix set at 12 pounds preload. When the sled is on the stand, I can see both clutches shifting out nicely so I think we have the secondary assembled correctly. I was able to get the sled out and play for quite a while today and got some more data to play with. First of all, the sled rocks! Engages now at 5400 rpm, still topping out at 7600 on the Koso. When the sled is at the 100' mark, it wakes up and goes! Incredible for a 440. The top end is still unknown at this point, I believe the track was expanding and began to ratchet on the drive cogs. Something made more racket down there at higher speeds at first then even when I did holeshots so I'll have to look around. I did back off the track tension quite a bit when I was fooling around with trying to reduce any drive friction. I'll tighten it up and try again tomorrow to see if the ratcheting goes away. Another thing I was able to play with was the Koso gage. It displays and warns you if things exceed the programmed temps and it does record the highest exhaust temp also. Playing today with wide open runs, the highest temp recorded was 1153 degrees (PTO) and 1180 degrees (MAG). Wasn't sure if this is in the ball park for optimal temps for my main jetting. Plugs do appear a bit dark and oily but it runs so good. I imagine once we get the rpm's up there, it may run a little hotter? I am also going to try increasing the clutch center to center distance just a tiny bit. Maybe the belt isn't truly bottoming out in the secondary and topping all the way on the primary, there is a little black marker left at the very top of the primary, so maybe.... Now that the sled is flying, I need some better brakes. I disassembled the original brake assembly, cleaned and polished all sliding surfaces and it seems to work but it doesn't slow down the sled enough. Do you guys recommend a different set up using hydraulics? I'd hate to earn the nickname of "Splat"! Oh well, I'm having a ball! Until next time..... On a Arctic RC thats a lot of cam and spring unless your just putting around. Something like a Scorpion 440/Cat 6000 should work better. 48/44 cam to let it wind out once under way or just a straight 45 with 43-44 gr weight. It came with a Black but White is closest available now. You cant bottom out the belt in the secondary with room to shift in the drive it will blow a belt. Your speed says your not too deep in the secondary at stock CD |
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Post by midniterupper on Jan 2, 2020 16:49:52 GMT -6
Cool! More excellent thoughts and input, sure appreciate everyone thinking about this situation. I have thought of running the sled temporarily without the cans just to see. That may be in the works.
Regarding the clutching, I agree with trying something different with the secondary. I went to our local salvage yard in Mt.Pleasant last month and picked up several cams and springs for the reverse secondary. Kinda waiting to try them out due to my priority of focusing on getting the rpm's up, even on the stand. I think you're right with the multi angle helix. I'm a big fan of taking notes when we change anything, love to review them later. Of course, well continue trying one change at a time when we do get to test. I never could multi-task!
Now today I had a chance to do a little work to the sled. Changed the mains from 310 down to 300 because of the temp readings on the EGT's. Stayed in the same range. Tightened up the brake assembly, got it to lock up the track now so I'm happy with that for now. Tightened up the track to 1" clearance with 10 pounds of down force to see if that would help eliminate the returning ratcheting noise and vibration. It didn't. I think something must have came loose with the tensioner set up. Gonna tear into it again tomorrow to see what's going on in there. May have to strengthen the tie bar. But, while I have everything apart, I'm going to run the motor and drive train without the top gear on so I can observe the shift out and the RPM's. Very curious to see the results.
Also today while I had the sled on the stand, I wanted to record a baseline for the top RPM achieved while just running on the stand. Using both tachometers now, the digital read 7900 RPM, the recording tach only read 7700 rpm. I'll go with the digital reading! We're getting there for sure. I have been using some Arctic clutch arms (#502-44.5) that were supposed to weigh 44.5 grams but when I weighed them individually the lightest was 44.3 so I matched them. Didn't make any difference in rpm so now I want to fool around with a spare set to lighten them up to 43 grams just to see the difference then. Got a busy day tomorrow, I will let you know the results and findings. Thanks again!
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Post by mrrupp1 on Jan 2, 2020 20:35:26 GMT -6
I just looked at my 76 nitro oval race sleds secondary. It's a older reverse secondary and I have a 45 degree helix with a white spring at the strongest setting. The primary is a Comet 102-C with yellow green spring and modified C cam arms, not sure there weight. The engine is stock inside, but I do have Rupp pipes modified to there mods specs and no mufflers. The carbs are stock 38 mikunis with no air box. Sorry about all the rambling, I just wanted you to know something about the set up. Now to the point of all this is the motor runs right at 8200 to 8300 with really no problem. I have run it on a stand and I have seen it hit 8800 to 9000, but that is with a stock Rupp tach. I have, give or take 20 or so Rupp liquids either in pieces or together and I hopefuly found the best tach. I was thinking the same thing as mutt maybe the helix is a little to aggressive and not letting the motor wind up. Just a thought. Clint
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Post by midniterupper on Jan 3, 2020 1:00:32 GMT -6
Hey, Thanks for sharing Clint! Your set up is giving me a lot of valuable information. I have a white spring for the secondary and a 45 degree helix also that I picked up last month. Haven't tried any of it yet. I still have the old comet here too though I will need to repair or replace it as it had a small crack developing in the stationary sheave. I did like the yellow green spring in the primary. I have not been able to locate the Comet modified C arms, I'll keep searching for them. It would be helpful to have another set of clutches to swap out while testing as well.
Good to hear that your motor isn't too much different than mine. The motor is pretty much in stock form, I stuffed the crank, cleaned up the ports by just removing the blobs of casting and polished the exhaust ports. The timing is now at .100" BTDC, running with K&N 40mm taper cones (tapered and polished the intake bell on both carbs). Installed Boyeson reeds. Stock exhaust with cans so nothing too fancy. Sure sounds strong at all times but that's just Xenoah! We'll keep at it, Thanks again Clint!
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Post by midniterupper on Jan 3, 2020 18:34:26 GMT -6
Well I did some more work to the sled today. Ended up removing the chaincase cover due to the returning ratcheting noises and found the rear roller arm bracket bent releasing the tension applied by the tie bar (which held up!). It looked like there may have been interference between the roller pins and the case cover also, may have kept the rollers from being able to pivot when tension was applied. That explains why there wasn't any noise at first, then when the arm bent it just got worse. I made a new adjustment set up with the roller tensioner. Fabricated a couple of 5/32" stainless plates (1"x 3") that sandwich the forward side of the case. I drilled and tapped a 1/2"-20 hole using a bolt and two locking nuts that apply pressure to that side of the chain. It pretty much copies the same set up used on the '97 Thundercat so it should be strong enough to keep the chain tension correct. The Arctic chaincase didn't use the stainless plates, just thought it would strengthen the set up.
I also performed the test I have been wanting to do. I removed the upper gear in the chaincase and was able to run the motor and shift out the clutches completely. Before I could run the motor I had to reinstall the cans, hook up the pipes and refill the coolant but that's normal I guess. I let the motor warm up and ran WOT several times and made some interesting discoveries. First, it was really helpful to see both clutches fully shift out. The belt in the primary goes all the way to the very top, actually exceeding the pulley diameter by about 1/8"! Hung right in there though. The secondary also shifted completely, sucking the belt all the way down to the bottom of the clutch. Belt freeplay appeared great as did the alignment also. It was refreshing to see.
Now when I did that test, the rpm's did go all the way to 8500 when just free-wheeling. I didn't keep her pegged out, just let her climb as quickly as she wanted to then let up to go back to idle. Like I mentioned the other day, I have both tachs mounted on the sled for now and it proved to be a good thing. While idling I noticed the VDO tach is reading 400 rpm lower than the electronic Koso tach. I know someone mentioned the VDO tach possibly not being accurate and I believe they are right. When revved up the Koso reads 8300 while the VDO reads 7900, which is where we were spinning at on a couple of our test runs, so we must be close!
While revving the sled up without the upper gear on, I noticed a weird pattern on the way the rpm's increased. It was like the motor would first try to achieve 7,000 and then quickly go to 8,000+. It was like a 2 speed transmission: go to first then hit second. It did it very quickly, but rather consistently. Almost like a bog when you peg it at the starting line. I don't think I ever noticed it when we tested though. Maybe that's normal if we run the sled without the chain attached? Never did that before, always wanted to though. Pretty interesting...
Hopefully I'll be able to get everything back together tomorrow and get back to testing, there are some Vintage radar runs up here for the next two weekends. Would love to go play. Keep ya posted! Thanks again to everyone...
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Post by Ruppsforever on Jan 4, 2020 11:00:10 GMT -6
Cool !! So you should be real close on your clutching but still lots of room for improvement. Make changes and write down the results. Like I said a long time ago I found that spinning the motor at 7900 to 8000 resulted in the best 500' times. You still should try Polaris 10MW weights and get a less steep helix and play from there. I think those cat weights you are using right now are almost identical to the Polaris weights. So you might be good with them also. The Polaris 10 MR or 10MW profile is a very aggressive profile unlike the comet weights. You will find that they pull a lot harder than those flatter looking comet weights.
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Post by upmagnum on Jan 5, 2020 6:13:21 GMT -6
 The custom black Magnum I built a few years back was running a comet with a gold spring and 10mw weights on a stock motor and ran very well. Guy I sold it to said he was going to use it as a speed run sled. He called me this fall wanting to know if I had any more sleds I wanted to sell. Said he had the Magnum out 5-6 times and it hadn't been beat yet. |
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Post by Ruppsforever on Jan 5, 2020 10:48:29 GMT -6
That is such a beast Joe. I forgot about that sled.
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Post by upmagnum on Jan 6, 2020 13:09:22 GMT -6
That sled was sort of a test build for the one project I have been hanging on to. When I compared the parts from mine to Bill's they pretty much are a match right down to the weird brake set up except for the pipes, but mine do match what I saw when I saw the sled race in Jan/77. Now if I could just come up with an aluminum bulk head(mine was damaged and scrapped by a previous owner).  |
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Post by mrmotors on Jan 6, 2020 22:41:16 GMT -6
I won't put his name up here Joe but there is a fellow making the aluminum bulkheads as I have purchased one from him. Rick Weaver can tell you who and probably put you in contact, or you can PM me and I will give you a name and phone number. It would probably be OK to put it up here as he was on Facebook with them but I will let one of the other guys do it just in case.
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Post by midniterupper on Jan 15, 2020 13:21:13 GMT -6
Well, it's been a while since I was able to post anything new on the old Nitro. This years flu going around is a rough one, knocked me down for over a week but I'm getting better. Only an E.R. visit turned things around so be careful out there, for a while I felt so bad I thought I was riding a Yammie!
I was also getting discouraged with the Nitro because I kept having gremlins with the drive train, things just not making sense, but today I found the problem. Tell ya what has been going on.
When I would spin the secondary by hand I could feel high spots or spots that were harder to turn than other spots. Felt like when the track drive lugs engage with the drive sprocket so no big deal right? Seemed to spin easily enough by hand and when the clutch engaged under power, seemed rather normal. After all, we have (You Have!) got the RPM's right where they should be, engaging great, have a super set-up for the drive chain tensioner, using 13 wide chain and sprockets verse the 11 plate, jetting temps are consistent at 1150-1200 degrees and the sled is a ball to ride! Well, the right side track drive sprocket separated at the flange and is flopping around! I couldn't see the break until I put the sled way in the air to study everything while verifying the track alignment and tension, attempting to eliminate the returning ratcheting noise issue along with a new problem I never had before.
The problem's symptom was: Engage great at 5700 rpm but then immediately drop down to 4700 once the track began to spin (on the stand). Like clockwork, consistent and smooth. Like it was supposed to do that, though the sled never did that before. I believe we got it now. I replaced the drive sprockets last September so now I need to find some stronger replacements. Please let me know a good lead. Keep you posted on the findings!
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Post by Ruppsforever on Jan 15, 2020 17:40:07 GMT -6
Glad you are feeling better !! That doesn't sound good at all !! Where did the drive sprocket break ?? Was it an aftermarket drive sprocket or OEM ?? I have never had a drive sprocket blow apart. Must of had crack in it from the beginning I'm guessing. Glad you found it !!
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Post by mrrupp1 on Jan 15, 2020 19:12:50 GMT -6
I was wandering what was going, because we haven't heard from you in a while. I remember a couple weeks ago you said you might take the sled to some radar runs and see she does. I'm sure glad you are feeling better, that flu is a killer. I'm with Ruppsforever, I have never blown a drive sprocket up. I have broken a roll pin or two, but never a sprocket. I've never used an aftermarket drive sprocket just always OEM. Well it sounds like you found the problem. Can't wait to see how she does. Clint
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Post by midniterupper on Jan 16, 2020 7:23:54 GMT -6
Hey, Thanks for all the well wishes! Should be strong enough to tear into the sled today, It's a big job to remove the drive shaft and drivers but actually the sled comes apart rather easily compared to some of the newer models as we all know. I never broke a drive cog before either. I believe the driver that broke may well be an aftermarket being that it is green in color, got it from Pipestone so I'll give Kevin a call for replacement. I have the original drivers yet also so I will measure them out and see if they may still be of use too. The right side driver is the only broken one, it busted right where the driver starts to radius out from the bushing area where the pin is located. I used new pins too. When I get it torn down today will look at it to see what caused the problem but I think you are right, it must have had a crack in it from manufacturing originally.
Boy, we sure have had some odd problems with this one haven't we? I sure appreciate your help, never would have gotten this far without you! I still love learning, keep you posted with the progress here. 3 Vintage events in our area this weekend, driving me nuts that I am not ready to attend but we'll get 'em. Until next time.....
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Post by midniterupper on Jan 16, 2020 13:56:14 GMT -6
 Okay, here is a picture of today's findings. Appears the left driver spin just a little, right side couldn't handle it. I think the spring roll pins are a bit too short for the hub diameters. Attachments:
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