1976 Nitro Grass Drag Set Ups

[mrrupp1]

I hope everything is ok with the sled. Clint

[mrmotors]

C'mon now, we can't be havin no ru-roh's now!!

[midniterupper]

Okay, just a quick update this morning, got some sledders staying the weekend for riding so we'll be busy but having fun! I took the sled out yesterday to play around a little and try a pass or two. Sled sounded strong of course but when I kept her pegged, I did notice something definetly bringing down the rpms when going around 50 at 7800 rpm. Dropped about 300-400 rpm,and made a strange noise like a bearing squeal. Real brief though.
Then I made 1 pass down the track, about 150' into it, the sled started ratcheting somewhere. I'm not sure yet if it is the track (which I doubt, it's still pretty tight) so I'm thinking something isn't right with the drive chain. I didn't push it after the run, just limped home and let her thaw out. Maybe the drive chain is too tight or something, I'll look at it a little more today.
As always, keep you posted!

[mrrupp1]

Glad to hear the engine ok. Clint

[midniterupper]

Hey, What do you know, I finally got a chance to do some work on the sled. Been thinking about it like crazy, just needed some quiet time with it. So in that regard, here is the latest.
I looked under the tunnel/track clearance area and noticed I still have interference with the .875" studs and the front portion of the tunnel. Chewed it up a bit but no serious damage to the aluminum tunnel, just a lot of new claw marks. I need to increase the clearance in that area in order to run my studs, so that will be on the agenda for sure. Any and all suggestions will be helpful, I know the oval racers must have a trick to gain the necessary clearance for their studs. The rear portion of the sled has plenty of room now, the rear suspension has never been so smooth too. Not bad, certainly fun for around here just not sure if I would want to log 100 miles on it for the day!
So that is where some of the noises originated from that I first heard last week while sorting some things out. Must have been the studs hitting the forward tunnel so we'll have to fix that. Now I got into the chaincase once again to investigate noises coming from there too. I found the chain tension was just too tight using the Cat springs with the 20/39 gear combo so I resorted back to the single roller and bolt tensioner set up. Also noticed rubbing on the upper bearing support bracket inside the chaincase from the new wider 13 plate chain, so I took care of that noise. Gear alignment is perfect, everything appears to be rolling much smoother in there now so I buttoned that back up.
To be sure I would not hear other noises caused by the studs, I removed them all temporarily. No noise coming from there now.
Refilled all fluids and took the sled out to play around a bit. It ran great, nice and quiet with no noise coming from the chaincase or drivetrain. I made several passes on the closed road, taking it easy at first then increasing my speed with each pass as I listened. Got up to a steady 75 mph without issues until the sled gushed hot coolant out of the fill cap. First time that happened, maybe had a air pocket in the system that I didn't get purged. Made it back to the shop but it shut off when I pulled it in. I let it cool off then tried to start it but it wouldn't. Squirt fuel in the plug hole and she starts right up then died. Looked at the fuel filter and it's empty. So now my fuel pump has died which is no big deal but I would like to keep the original style fuel pump that mounts to the crankcase. I haven't looked at it yet to see if it's just a normal 2 outlet Mikuni rebuild kit. I'll have to secure a kit before I can run it again, that'll give me time to address the stud clearance issue.
So overall the sled is coming together, we're eliminating problems as they arise. It was good to take the sled out today and play "speed runs". Top exhaust temps today at prolonged wide open throttle was PTO 1225 degrees and MAG was 1200 so that looks good. Belt marks at the outer edge of the primary clutch verify it's fully shifting out. Top rpm's today (without studs) was an easy 8000-8250, though very brief while shifting out.
That's about it for now from this end, we'll keep you posted as I get it back up and running again. Until the next time -Paul

[mrrupp1]

Hi Paul, the fuel pumps are regular duel feed mukuni fuel pumps. they just take the standard kits. Central snowmobile part number was 450 or part number DF52RK. One thing I would make sure is the O-ring on the mounting block is good. The size of the O-ring is 3mmx8mm. As far as getting more clearance in the front I have never had to do it so I'm not sure the best way to approach it. I know some put in smaller drivers or roll the chain case. I'm sure you know better then me. Sound like she running pretty good. Keep up the good work. Clint

[midniterupper]

Thanks Clint! I'll check into the fuel pump kit and o-ring, sure appreciate the info. I'll keep you posted on our progress here

[midniterupper]

Well I have an update on the sled's current status for the moment. I got the kit for the fuel pump and when I disassembled the pump water (coolant) was in the pulse chamber of the pump. I wondered how it got in there but put it all back together and started the sled. When it fired up, coolant came blowing out the exhaust cans and sounded rather flat. Shut it off, checked the plugs and the PTO plug was very clean so I knew we blew a gasket somewhere.
I drained the coolant and removed the cylinder head, no apparent leak there. I applied YamaBond to both sides of the gasket when I reassembled the engine last spring. That stuff really held! I should've put some on the base gaskets too while I was at it, I think that is where our leak is coming from. I still need to remove the cylinders to see for sure.
Okay, got more company up here for snowmobiling and they are getting impatient with me. They want to go play and need me to lead.
Chat soon, thanks again for your interest!

[mrrupp1]

Hey Paul the base gasket doesn't seal any coolant. I thought I would let you know, maybe save you some work. Hope you can get her back together for minimal cost. Clint

[midniterupper]

Wow! Thanks Clint, I didn't know that, I'll have to figure out where she's gushing at. I didn't have a chance to pull the cylinders yet so maybe that's a good thing. I'll check all the hoses, it seems to be originating from the left side of the engine and the PTO cylinder was full of coolant. I have a few machining jobs that came in so I have to focus on those for a few days but maybe in between cuts.
Got me wondering now! -Paul

[midniterupper]

You were right Clint! The cylinder head gasket is composed of a stamped metal ring along with the normal fiber gasket material, this one was made by Windrosa. The metal ring burned right through near the water jacket. Had to really look closely to see it at first but it's the problem. Spoke with Kevin at Pipestone today, he's got the solution with a all metal gasket. I'll get it ordered tomorrow, gives me time to get a look at my clearance problem in the forward tunnel area.

[mrrupp1]

I'm glad you found the problem, can't wait to see back on the snow. Clint

[Ruppsforever]

You sure seem to have bad luck. Hope it changes soon !!

[midniterupper]

I know right? But it's so worth it! I guess it's like a chain, one link at a time. We're getting there:)

[mrrupp1]

I agree with Ruppforever, it seems like when you get something fix something else breaks. Its like me about five years ago I decided to get back into drag racing after a 25 year break. My buddy called me up and said I got a motor you have the car, lets go racings. We put a better cam in it and rebuilt the heads a went racing. Raced the whole season with no trouble to speak of. So naturally the car needed to go faster, so we pulled the motor and stroked and bored it. Custom cam big high flowing heads lots of compression, the list goes on. First night out the car was way faster till we broke a rocker arm. Undated the rockers, took the car back to the track and when it got hot we loose spark. It seemed like ever time we turn around something gave us trouble. So I guess what I'm saying is I feel your pain, but in the end it will be all worth it, because I believe you are going to have one mean Rupp that is hard to beat. It was for us with all the little quirks we had with the Mustang at end of the season she ran really good and was super fast. I guess in the end it's just called racing. Hang in there Paul. Clint

[midniterupper]

Thanks for the encouragement Clint, it really means a lot coming from you. I know what you mean though, whenever we push things a bit we will always find a weak link in the chain. In all reality, I am glad things are breaking here at home rather than at the track. Much easier to fix, and there is no embarassment or comments from the Yammie camp. I am confident this sled will run great, just have to think outside the box and make the changes, I'm sure it will work out.
The new metal head gaskets from Kevin Haase showed up today, they look strong. Not cheap, $125.00 for the set but if they hold up they will certainly be worth it. Still scraping the old gaskets off the head and cylinders, the Yamabond sealed up well but sure is a pain to get off! Might have time tomorrow to reassemble the engine, will have to measure the squish value with these new type gaskets. I don't know if these are re-usable once I compress them or not. Once I get the motor back up and running then I will attack the stud clearance issue.
Thanks again Clint, hope all goes well for you too!
-Paul

[mrmotors]

Always the way it works, chasing successive problem around until you get all the little issues taken care of..."The price of progress is Trouble!" Sir Hives of Rolls Royce..

[midniterupper]

Excellent words of wisdom! Problems are no match in comparison of creativity of an old man, focus and persistence (along with boredom) shall prevail. Onwards and upwards, we'll get her running today
And the Adventure continues.....

[midniterupper]

Okay, She's back up and running and sounding great! Still have a little air to purge out of the cooling system but it's running quite nicely. Heated the motor up a couple of times and rechecked the head bolts torque, so far so good.
Checked the squish, both are at .075" and the compression is 148/149 psi. These readings are using the new metal gaskets from Pipestone, the difference between the old fiber/metal type is only .003" when torqued down. Great looking gaskets, excellent craftsmanship and quality.
Now I shall attempt to conquer the stud clearance issue, keep you posted!

[mutt]

I dont think you have any worse luck than anyone else bringing a dead sled back to life. I'm not even that far find something wore out take that off find other things just as bad underneath. Even came to the conclusion that its not going to roll this season. So I went medival on it this week. Did Rupp use any steel drive shafts because mine has one and of coarse has a spun bearing and only 1 1/8 now. Very good looking track no rusty clips non studded. When pulled out a little slight stud rash near the front. Had studs at one time and no tunnel protectors think it could should have been worse. Wore out front cross shaft so the wheels I found for the rail tips now rub. Wont even talk about the recoil. The only good thing its fun to mess with this sled