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   Author  Topic: 76 340RV problems  (Read 133 times)
rkalter
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76 340RV problems
« on: July 31, 2017, 08:10:59 PM »
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The first step is admitting you need help lol. Hellllp.
I just had my cylinders machined to 40 over. The ring gap was at 0.45mm.  Specs say from 0.2 mm to 0.5mm so the machinist did a poor job in my opinion but would this alone yield a compression value of only 100 psi or is there something else wrong. What compression numbers should I be seeing on this engine? It won't even fire up. I've got good clean strong spark. I've checked the timing on rotary valve and stator twice. I do have a 1976 Skidoo RV340 shop manual that I'm following religiously. Lost and confused.
Ray
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1970 Skidoo TNT 292 Ratsled
1971 Skidoo TNT 340
1971 Skidoo TNT 775
1976 Skidoo RV340
1996 Skidoo Formula III 600
2008 Skidoo Renegade 600 sdi
Green and Gold
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Re:76 340RV problems
« Reply #1 on: August 1, 2017, 08:02:45 PM »
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Hopefully your shop had the new pistons in hand and fit the bores to them using the min piston to wall clearance number.  Some of the shops I’ve visited don’t do things that way, they bore without referencing actual piston size.(i.e, if a 63mm is the stock bore, 4th oversize would be taken out 1.0mm to 64.00mm)  This can certainly introduce error;  I’ve had  aftermarket pistons  that were supposed to be the same diameter vary in size.  Things get worse if the same machine shop bores in inches and your piston was forged/cast to metric measurement; .040in converts to 1.016mm 
So what’s your piston to cylinder wall clearance?  That would be the clearance I'd be most concerned about.  Hopefully you have a good set of T gauges and micrometer available.... 
To the issue at hand, I’ve had low initial compression on fresh top end jobs; it sometimes takes afew minutes of running to seat the rings into the freshly honed cylinder walls and then compression climbs.      Somewhere between 95 and 100 PSI (measured on my comp gauge, readings can vary a lot between gauges) is what it takes for my F/As to start.    Assume you’ve added fuel directly to cylinders in your attempts to start?  You could also try adding some 2 stroke oil directly to each cylinder (thru the plug hole) and then a few drops of gas to see if you can get your initial start that way.  New plugs would be a good idea too. 
Good luck.   
« Last Edit: August 2, 2017, 06:38:40 AM by Green and Gold » Report to moderator Logged
rkalter
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Re:76 340RV problems
« Reply #2 on: August 8, 2017, 06:56:55 PM »
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Hello Green and Gold. The shop was supplied with the new pistons and rings along with my shop manual for the exact specs required with the page book marked. The boxes were never opened and the rings were still wrapped in their packaging when I got it all back. They never measured anything except the bore.
I do not have the tools to measure either the bore or the piston for you. But I can tell you it slops from side to side quite a bit with the piston rings on!! And that the ring end gap was at the end of spec 0.45mm for specs 0.2 - 0.5mm.
I have added fuel directly in spark plug holes too. No difference. I am using new plugs.
I found a bad spot in wiring harness that may have been causing some issue. Couple wires rubbed bare. I went through all the wires and fixed the one bare spot I found. Now it bucks and farts but still won't start. I have slowly moved the stator plate from one side to the other and back in small increments with no change in firing. Just bucks two or three times. Just a quick pop pop pop as I pull it over and then nothing.
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1970 Skidoo TNT 292 Ratsled
1971 Skidoo TNT 340
1971 Skidoo TNT 775
1976 Skidoo RV340
1996 Skidoo Formula III 600
2008 Skidoo Renegade 600 sdi
Bones
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Re:76 340RV problems
« Reply #3 on: August 9, 2017, 11:07:28 AM »
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Try switching your spark wires to opposite sides to what you have now.
Bones
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mikesskidoo
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Re:76 340RV problems
« Reply #4 on: August 9, 2017, 12:23:48 PM »
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I had very very similar symptoms an my issue as it turned out was lack of compression..... seemed like it would "run" as you were pulling it over... but would not quite run on its own.. found my compression leak and fixed...fired right up. best of luck
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rkalter
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Re:76 340RV problems
« Reply #5 on: August 9, 2017, 03:09:27 PM »
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Quote from: Bones on August  9, 2017, 11:07:28 AM   

Try switching your spark wires to opposite sides to what you have now.
Bones
hi Bones. I forgot to mention but I did try swapping the spark plug wires back and forth as well as the trigger wires. Didn't work. When I switched the triggers I lost the attempt to fire so I switched back and it began popping and farting again.
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1970 Skidoo TNT 292 Ratsled
1971 Skidoo TNT 340
1971 Skidoo TNT 775
1976 Skidoo RV340
1996 Skidoo Formula III 600
2008 Skidoo Renegade 600 sdi
rkalter
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Re:76 340RV problems
« Reply #6 on: August 9, 2017, 03:10:30 PM »
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Quote from: mikesskidoo on August  9, 2017, 12:23:48 PM   

I had very very similar symptoms an my issue as it turned out was lack of compression..... seemed like it would "run" as you were pulling it over... but would not quite run on its own.. found my compression leak and fixed...fired right up. best of luck
where was your loss of compression??? Maybe I have a similar problem. Thx.
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1970 Skidoo TNT 292 Ratsled
1971 Skidoo TNT 340
1971 Skidoo TNT 775
1976 Skidoo RV340
1996 Skidoo Formula III 600
2008 Skidoo Renegade 600 sdi
mikesskidoo
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Re:76 340RV problems
« Reply #7 on: August 10, 2017, 05:41:01 AM »
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mine was due to poor machining on the cylinder heads, pressure was leaking down the holes the cylinder studs run through, but because it wasn't leaking out where I could see it, it took a long time to find the problem, which is my fault 100%, I stupidly ASSUMED that.."this is a newly rebuilt engine it cant be the compression?!!" 
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