670 probs, sorry so long

[lew]

i am new to the site and i am looking for any info to help me. ok well i bought a 1995 mach 1 670 from a guy and when i got it home i tore down the top end and put new jug and head gaskets on it well when i was in there i noticed that the pistons were brand new oem bombardier pistons and the jugs had a fresh crosshatching on them. so i put the gaskets in it and lubed the cylinder walls and put everything back together and it ran great. i took it out a couple of times and it screamed. well the third time i took it out i noticed it was running like crap.

so i took the plugs out they were burning fine but not quite as "chocolate" as it should have been. so i tested the gas and it had some water in it . so i then added 1 can of fuel deicer enough for approx. four gallons and put five more fresh gallons in it.. made it about 25 miles and blew a piston. i took the piston out and took it to a machanic with the jug and he said it looked like detonation. the edges were all chipped off.

so i put it back together with a new piston and ring kit the jug looked fine luckily. well i got all the specs for the motor and carburators and went through everything changed crank seals reset rotary valve. checked for bent crank. it has stock jetting pto 430 and mag 410. put it together fired up ran great. made it 1.5 miles and blew the other piston. same prob. now im thinking jetting any idea's

 

[Polarblu]

ya your jetting is backwards i take it you melted the mag side? that side needs more fuel.

 

[magnet]

ya your jetting is backwards i take it you melted the mag side? that side needs more fuel.

?????????????????
every book i have ever seen with jetting specs has the pto side fatter as it gets hotter because of the clutch heat. if we read his post he melted both pistons. they are coming apart by the sounds of it. if it is in fact jetting you will probably have alum. on the electrode of the spark plug. are you getting any oil? pump fubared maybe? just grasping straws here. at 430 and 410 you should be way fat i think as my 99 670 ho from factory is only 340 and 350 on the pto side. and it flowed way more air than the 95 670s did.

 

[JBDoo]

Check your squish, I bet it has too much compression for pump gas and you are breaking the pistons with detonation not a lean problem. What does it test on a compression tester? those engines used a thicker base gasket, maybe you have a thin one in there now, go to the thickest one you can find and I bet you are golden.

 

[Polarblu]

?????????????????
every book i have ever seen with jetting specs has the pto side fatter as it gets hotter because of the clutch heat. if we read his post he melted both pistons. they are coming apart by the sounds of it. if it is in fact jetting you will probably have alum. on the electrode of the spark plug. are you getting any oil? pump fubared maybe? just grasping straws here. at 430 and 410 you should be way fat i think as my 99 670 ho from factory is only 340 and 350 on the pto side. and it flowed way more air than the 95 670s did.

My apologize but you run more fuel in the mag side the pipe puts out more heat. It has always been that way, since Christ was a cowboy. What books do you read? Might be a TRA thing?

 

[lew]

well i went to my local bombardier dealer and they printed me out the specs for my sled. apparently the 95 mach 1 was the only year that came stock with twin pipes. and yes thats what the specs called for was pto 430 and mag 410. and yeas the electrode is covered in alum. both times magnet. and jbdoo the gasket kit that i bought did have three different thickness gaskets. im not sure off the top of my head which one i put in it but i will check tomorrow. and also how precise is the degree setting have to be on the rotary valve. because i just made sure that the mag port was just all the way open when mag side was at tdc.

 

[Polarblu]

ok im learning something new...... why the diff thicknesses? effects timing for sure but this is the first i have heard of it. Is it a 670 thing or just the older units?

 

[lew]

im when they stopped making the rotary valve motors but yes they have a plate that spins with the rotary gear and it opens the mag side when it needs to be open and it opens the clutch side when it needs to. and im not sure why the diff thicknesses i dunno if it comes with one for the summit and one for the ho or what

 

[Polarblu]

i was asking about the base gaskets. The rotary valve is extremely simple.

 

[Modman]

the gasket set comes with three different thicknesses, you count the holes on the gaskets and it tells you the thickness. If you count the holes on the remaining two base gaskets left in the kit, you can figure out which one you installed by the process of elimination, I think they are like 4 thou, 6 thou and 8 thou or something like that, honestly I can't remember though. I can measure for you, I have a complete spare set in the garage. will do shortly.

It is important that the rotary valve be set correctly, you should really use a degree wheel or get the specs for TDC, not just set it to mag side full open unless that's exactly how it was when you removed it.

 

[lew]

well i did get specs for that and i have set it but still blew other piston. do you know which gasket my sled calls for?

 

[Modman]

well i did get specs for that and i have set it but still blew other piston. do you know which gasket my sled calls for?

no sorry I don't know, but it depends on how much much thickness you want to run. you can run any of the three but it will change your port timing and your squish clearance depending on which one you choose to use.

 

[lew]

ok what exactly is squish clearance and it will change my intake port timing you said??

 

[Modman]

ok what exactly is squish clearance

distance between the top of the piston and the bottom of the cylinder head. smaller "squish" means more compression and that means you need more octane. If you are running 89 octane pump gas and using the thinnest gasket you might need to run more octane because you are detonating due to the higher compression.

Or you are too lean. Start big on the jets and work down slowly.

 

[lew]

ok now when you say start big do you mean open the jet in the side of the carb more probably sounds stupid but im not sure on it

 

[Modman]

ok now when you say start big do you mean open the jet in the side of the carb more probably sounds stupid but im not sure on it

no i mean change your main jets to something bigger like 480's and start there, then start leaning down instead of starting with the recommended jets and finding out they are too lean by burning up pistons. but.... I don't think jetting is your problem since the mechanic already told you it looks like detonation and you said the plugs are not quite as dark as chocolate. Get a compression tester and check your compression once you get it all back together. Sorry I can't help you more but you are trying to internet diagnose a problem that you don't know what it's being caused by. First you need to find the cause, then you apply an appropriate solution. You can't start with applying solutions to problems that are not causing your issue.

For example - you could take my suggestion of re-jetting and you can jet really fat but if you have too high of compression for the octane you are running you will still wreck pistons. You'd call me an idiot and you still have a busted sled again, when all along it was compression (or an air leak or whatever). You would have applied the incorrect solution to the problem that you have, just based on a suggestion. your plugs are already telling you that you are likely not lean (at least from what you described).

My real suggestion is you check compression and pressure test the motor to figure out if its got any other air leaks, then at least you have eliminated those variables.

 

[gr8tdragon]

I agree with Modman. Check your compression. When you bought the machine from the previous owner did you ask them if they made any changes to the engine. The big one is if they milled the head, then did a porting job to the engine. These 2 items will definitely change your jetting to have to be richer. Are you running stock air box or pods? Again changes jetting. Factory jetting is for a engine that is set up the same as factory. Again Modman is right check your compression first. It won't tell you if any of the hidden changes are there but give you a possible idea. You changed the jugs so you eliminate the porting affecting the jets. Ensure you have that rotory valve in the right place as 5 degrees out most likely spells the end of at least one cylinder if not both. Make sure the rotory valve has not been modified. Look into everything before buying parts that you don't need.

 

[97mxz670]

my 97 mxz was jetted 300 and 270 stock idle air screws at 1.5 to 2 turns out..and check ur slide position it could be leaning it out at high rpm..

 

[renegade x]

well i went to my local bombardier dealer and they printed me out the specs for my sled. apparently the 95 mach 1 was the only year that came stock with twin pipes. and yes thats what the specs called for was pto 430 and mag 410. and yeas the electrode is covered in alum. both times magnet. and jbdoo the gasket kit that i bought did have three different thickness gaskets. im not sure off the top of my head which one i put in it but i will check tomorrow. and also how precise is the degree setting have to be on the rotary valve. because i just made sure that the mag port was just all the way open when mag side was at tdc.

The 96 Mach 1 also came stock with twin pipes.95 and 96 Mach1's were virtually identical except for (BOLD NEW GRAPHICS) on the 96.They also came stock with 44mm carbs.I also believe the porting was a little different than a regular 670.:d:d:d

 

[lew]

well guys i know it has taken a long time but your help[ has paid off i finally got to take her out this weekend and WOW. that thing is sweet. ill upload some pics later today. it ended up being the mag side rave valve was broken and i didnt replace the inner headgasket ring and antifreeze detonated a piston on the clutch side. and the rotary valve timing was off. but i did jump the mag side up to a 420 though. thanks again guys.