kerry
L2 Scorpion - Above All
Posts: 69
|
Post by kerry on Feb 29, 2020 20:14:31 GMT -5
Hey guys having a terrible time with our whip this season and i'm stumped. The original motor was getting tired so I put a spare engine in I had.We had a few small rides but on a longer ride we lost the pto side to overheating. So I redid the whole motor with a new gasket and seal kit and a spare matched mag side cyl/piston head set I had.We did a ride of 60+ miles 3 weeks ago and it ran flawless.Temps were -28 celsius to -10 celsius (cold) for the day.It was left in the trailer for the week and we went for a ride the sunday and it blew a hole in the pto piston .It was -1 celsius about 30degrees fahrenheit. I spent the following time pulling it all apart.put a different crank in it,another spare mag cyl/piston/head and resealed.Timing is on the low side at .103 and gap is .015.It was at .106. Today we left for a ride and stopped 4 times as I checked plugs not long after the forth time it died on my wife.Soon as I lifted the hood you could see the heat coming off the pto side.I pulled the plug and saw the top of the piston was already cleaned off so I pulled it back to the trailer.When we got home,and I knew, it fired right up.I have no more spares left and likely will have to find another parts motor or get new pistons at least. I have 4 stock sized cylinders to play with that would likely need a light cleaning hone.BUT am I only going to have the same issue? Should the clearances be different on the pto side because its naturally hotter running? I use B9es plugs on that side, premium 91 only mixed at about 45 to 1.Seriously thinking about swapping out to a different motor.Wife likes to ride,we like doing 50-70 mile rides but i'm tired of wrenching away good eves trying to get it back on the snow.Could be fishing!! Kerry
|
|
|
Post by weverat on Mar 1, 2020 20:36:11 GMT -5
Hi Kerry, Yes, the pto side is notorious for over heating. Here is a thread that shows all the venting used on the late model Stings and TK's scorpionsleds.proboards.com/thread/691/1979-tkx-hood-vent-updateLong story short, cold air vented into fan, warm air vented out from under hood. You seam to have covered all the standard things that help, B9 plugs, back down the timing, carb on the rich side, etc. Another thing that helps is to keep the compression down to about 120, and you could wrap the pipe to help the heat out from under the hood. Also some of the guy's run .005 piston clearance on the mag side, and .007 on the pto. One more thing, be sure the free flow head is on the mag side in order to let the fan blow through to the pto side. I am sure you have covered all the bases, just brain storm-in here. Don't give up on the cuyuna, they are great engines!
|
|
kerry
L2 Scorpion - Above All
Posts: 69
|
Post by kerry on Mar 1, 2020 23:12:14 GMT -5
Thanks weaverat,I'm ordering new pistons and another complete gasket set.I guess i will get the micrometers out and check my cylinder sizing etc.I'm sure it must be a clearance and lack of air flow problem.Just confusing as the original motor ran two seasons in variable temps and we didnt have this sudden overheating issue.Unfortunately it just doesnt have the compression anymore but possibly the cylinders may still be useful with new slugs if I have to get the compression down.It was 136/140 before our ride.I havent rechecked it yet but im sure the pto piston is goung to have to be replaced anyway.I plan on opening up the mag head for sure and will make some sort of exhaust vent to the left side console outlet over the belt guard.I do agree they are a great running engine when working well.I have a hard time keeping up to my wife.She enjoys her machine to its fullest. Kerry
|
|
kerry
L2 Scorpion - Above All
Posts: 69
|
Post by kerry on Mar 2, 2020 19:06:58 GMT -5
I just checked my compression and the pto side is down to 110.I did manage to stop it before any pitting happened on the piston.So upon inspection of a carbon free piston I find its .020 over which leads me to believe it was leaned out obviously compared to the mag side running a single carb.So I guess I should have cleaned off everything beforehand to find that out rather than assume the mag side of the two spare motors were stock sized duhh. Anyway ive ordered new stock ones from MFG Supply and do have two good cylinders to work with besides the one already on the motor. weaverat my mag side is already at 140 so what is the best way to get the compression down to 120 other than burning it down lol. Thanks Kerry
|
|
|
Post by weverat on Mar 2, 2020 21:34:31 GMT -5
The cuyuna manual suggests adding another base gasket. Sometimes it takes 2 or even three base gaskets. Of course this raises the exhaust port timing, but not enough to actually make a difference.
If you have an assortment of head gaskets, you could use the thickest one.
I ice, and grass drag old Scorps, and never have a problem, but only go 500 feet. The Cuyuna's do not like to be run hard for a long distance, like for instance across the lake, or on a smooth trail. If you work them hard continuously for an hour, they will burn a piston.
Oh, another thought, you know the little tin welch plugs on each side of the cylinder. Cuyuna milled the transfer ports through those holes, and then plugged them with the welch plug. Well,I have found those plugs to be rusted through with little pin holes, and I burned a few pistons before discovering this. Now days I slather those little bastards with epoxy, and then sand the epoxy flush with the cylinder.
The epoxy must be flush,because the cylinders fit almost tight against each other.
|
|
|
Post by 80whip440 on Mar 2, 2020 21:35:29 GMT -5
On my later Cuyunas I did away with the insulators between the manifold and the jugs. Had an instance where I rode on day, parked it and went to ride a few days later and started hard and was real lean. Found the insulator on the pto side with a big chunk missing out of it, and all cracked due to heat. Chucked 'em both and just used gaskets, never a problem after that. I have seen someone was making them from machined aluminum, but as I ran a Mikuni the heat transfer to the manifold was not a problem.
|
|
|
Post by weverat on Mar 3, 2020 6:45:42 GMT -5
Yes, that is a good idea, those gaskets are definitely brittle, especially now that they are 40 to 50 years old.
|
|
kerry
L2 Scorpion - Above All
Posts: 69
|
Post by kerry on Mar 3, 2020 19:17:04 GMT -5
weaverat I can do double base gaskets as they come with 4 in the kit or I could cut thicker ones from a FelPro sheet.I did this for my intake the second time round and also lathered all around the insulators with three bond for extra insurance.
80whip440 I may consider going mikuni but not sure what size of carb or guts.If I ran across a TK or Sting I'd raid the mikuni/airbox and ignition and the cold air kit if it was there. Thanks for the input guys!
|
|
|
Post by 80whip440 on Mar 3, 2020 19:31:08 GMT -5
If I remember right, I used a 34mm Mikuni when I rebuilt the sled. Had to replace the carb mount studs with allen head bolts to fit the Mikuni rubber mount. My Whip when I got it has a series of holes cored into the front of the hood, I assume for more airflow under the hood. I squared it off and used an older Stinger hood vent to make it look more "stock". Added some screen to the vent to help keep the powder intrusion to a minimum. It seemed to work well, although I wonder if it was on the opposite side it'd have a better effect on the PTO side?
|
|
kerry
L2 Scorpion - Above All
Posts: 69
|
Post by kerry on Mar 7, 2020 19:55:07 GMT -5
Not such a bad idea if it was ducted directly into the fan cover be like cold air injection.Often wonder if drawing from behind as it does if its limiting the air flow. I have all summer to do what is needed to rebuild and cool it down and on top of that I have to do my xenoah for my rupp liquid.Going to be an interesting season next year.
|
|