Ski-Doo Snowmobiles Forum banner
1 - 20 of 30 Posts

·
Registered
Joined
·
395 Posts
Discussion Starter · #1 ·
Ok - I know like many of you - I am anal when it comes to maintenance on my sled. Anyway - with a big trip to the Gaspe Peninsula in Feb - and a perceived loss of power from when it was new - I figured that I would have the dealer change the pistons and rings "just to be safe" Anyway - the compression prior to the change was 130psi. And after the new pistons/rings it was 130?? *%@? Anyway I had a lengthy discussion with my dealer as to why the compression did not increase after the installation of the new set. Blah blah blah.

During the X-mas New Year Break - traveled up to "THE HILL" for our annual family snowmobile vacation....anyway conditions actually were not that bad onto of the tug. As I was breaking a new set of pistons in - I was running about 50-1 pre-mix in the tank and being careful not to stress the motor - (I know my thoughts on breaking a box in) anyway at about 40 miles I fouled a plug - not to surprising as I was not traveling more than 35 miles an hour - (leading a group of 15 sleds). Changed plugs - fired right up but would not idle. Thought maybe bad gas..Who knows - decided to head the group back to the parking lot - goosed it up to 50 - 10 miles later - it just went dark. I mean it was like someone hit the kill switch. Went to pull it over and the re-coil broke. NOT A GOOD DAY.

Dropped the sled off at my dealer last Tuesday. He just called and explained that the right side (Mag?) was shot. Scored the cylinder - needs new one now.

So tell me - what the heck happened. The mechanics have been pouring over the sled trying to figure it out. They ruled out lubrication - oil pump test good and the pre-mix is obvious. No air leaks - base gasket in good shape no oil residue anywhere - coolant looks good...BTW they were Cudney's Pistons and Rings - absolutely not the problem in my book.

Any ideas - where can I point him.
 

·
Registered
Joined
·
1,851 Posts
got2ride said:
Ok - I know like many of you - I am anal when it comes to maintenance on my sled. Anyway - with a big trip to the Gaspe Peninsula in Feb - and a perceived loss of power from when it was new - I figured that I would have the dealer change the pistons and rings "just to be safe" Anyway - the compression prior to the change was 130psi. And after the new pistons/rings it was 130?? *%@? Anyway I had a lengthy discussion with my dealer as to why the compression did not increase after the installation of the new set. Blah blah blah.

During the X-mas New Year Break - traveled up to "THE HILL" for our annual family snowmobile vacation....anyway conditions actually were not that bad onto of the tug. As I was breaking a new set of pistons in - I was running about 50-1 pre-mix in the tank and being careful not to stress the motor - (I know my thoughts on breaking a box in) anyway at about 40 miles I fouled a plug - not to surprising as I was not traveling more than 35 miles an hour - (leading a group of 15 sleds). Changed plugs - fired right up but would not idle. Thought maybe bad gas..Who knows - decided to head the group back to the parking lot - goosed it up to 50 - 10 miles later - it just went dark. I mean it was like someone hit the kill switch. Went to pull it over and the re-coil broke. NOT A GOOD DAY.

Dropped the sled off at my dealer last Tuesday. He just called and explained that the right side (Mag?) was shot. Scored the cylinder - needs new one now.

So tell me - what the heck happened. The mechanics have been pouring over the sled trying to figure it out. They ruled out lubrication - oil pump test good and the pre-mix is obvious. No air leaks - base gasket in good shape no oil residue anywhere - coolant looks good...BTW they were Cudney's Pistons and Rings - absolutely not the problem in my book.

Any ideas - where can I point him.
[snapback]263975[/snapback]​
Sounds like incorrect ringend gap, go after the dealer who repaired it, after all they are CUDNEY
 

·
Registered
Joined
·
351 Posts
Call Cudney and see what he says, could of been a bad batch of pistons. Not to bash anyone (especially Cudney) but it could of been a bad batch of pistons (anything can happen, no one is perfect) just a guess.

Read this post, this guy had something similar and he is not sure what happened as well http://www.dootalk.com/forums/index.php?showtopic=31273&hl=

Also do you have any pics of the parts, maybe post them and we can troubleshoot what may have happened.
 

·
Mod'n is my thing
Joined
·
6,288 Posts

·
Registered
Joined
·
8,113 Posts
key phrase...

...and a perceived loss of power from when it was new...
just real tough to tell unless the power is MUCH less and consistant, I know there are days I think my sled is not up to par then the next time out it seems like a beast, and I know it has got to be my perception... cause I know the sled is the same!
 

·
Registered
Joined
·
214 Posts
Same thing happened to my sled after I installed new pistons. Mag side piston and cylinder were scored. I had about 30 miles on the pistons.

I`m still not sure what happened, but it looks like antifreeze scoring.

Same thing happened to Revulator as well.
 

·
Registered
Joined
·
253 Posts
I had a family member who had the same problem with Bill's pistons. The worst part is everyone talked him into using the pistons. He really didn't want to. He wanted to use Doo pistons and rings. But 15min out the MAG side wiped out the JUG. We think its thermal expansion. Bill gave him a new set of pistons but that doesn't cover the jugs that were destoyed.
 

·
Registered
Joined
·
1,064 Posts
As many people as there are here on dootalk with excellent results with these pistons its pretty hard to blame them.... but easy to use as an explanation for the unexplainable?!? If that even made any sense!
 

·
Registered
Joined
·
345 Posts
Samething happened to my 600 with the cudney pistons with 120 miles on them as well it looked like anti-freeze scoring or snow ingestion. Screwed the cylinder as well. Mine was on the pto side.
 

·
Registered
Joined
·
14,289 Posts
I am curious if all you guys are miking the pistons and checking the bores with a dial bore gage prior to reassembling... Just to make sure every one has the necessary clearances.

You can buy reasonably good.. low budget mics and dial bore gages on ebay.. that work fine for low volume work (ie.. a guy in a garage that changes a couple of sets of pistons a year. This is cheap insurance to make sure you have adequate clearance.

Ever piston and cylinder ... has a size.. and they are not necessarily all equal.

The other thing is this could have been a combination of little issues.. that when taken as a whole.. caused the siezure.

1. slightly lean for the minus 10F conditions (when you are running lean.. watch the ambient temperatures..and yes.. some one said they were reading the plugs.. the porcelin or the electrodes? ) You could have been close.. but just over the edge.
2. possibly a little antifreeze left in the case.. wiped the oil during the first few minutes of running.
3. Oil added to the fuel tank, leans the engine a bit.. oil displaces the fuel maybe in combination with being cold (-10F) or am I mixing up the two or three seizure threads?
4. Running the engine too hard before it warms up... particularly when the parts are not broken in...
5. Heat cycling.. sounds good.. but I personally doubt it does much for you.. other then being part of a slow break in.. If clearanced properly.. the only thing that should be breaking in.. is the ring surface to the cylinder surface.
6. A slight air leak it is possible.. and you can use sealer or not use sealer with equally good results.. most of us don't use sealer because it is a pain to get off the next time you tear down, with good luck.
6. Several more pistons and engines and you are well on your way to becoming an expert. Lessons are costly as you and alot of us who have paid are dues already know.

I would certainly not put a new piston in a cylinder without measuring both so that I knew the clearance... ah yes.. that feels right.. feels like it fits good..rocks just a little.. but were we 0.0004" too tight for the way we are going to jet and the temps we are going to run. Lots of things to think about.

As for the cylinder in the pictures.. it sure looks like it would clean up.. when hit with a nice fine stone meant for use on nikasil.. The other thought.. are you racing.. do you need the 99. 8 % of the power? Or is 98.99% good enough for your application...??? Is it worth spending $200 plus shipping and a week or two down time to get that last minute scratch out??? Things to think about... a quick hone now.. and run it for the rest of the season.. then renik during the summer? Only you and "one" expert advising you can answer the question. As you can see on the forum.. there are a multitude of opinions.. and all or none could be right.. who do you believe... hmmm... Do you have a good engine shop or good mechanic near you that could advise you? Some one who has done 100's of these?

Just my 2 cents......
 

·
Registered
Joined
·
4,667 Posts
I have seen the pistons on here in a couple of posts and they can generally be explained what happened to burn them down, we have sold over ten thousand pairs of pistons and there are some isolated cases of burn down, but when you see 2 or 3 of them posted it may sound like a lot but it is about .00015% of the total sold and of those all of them have a reason as to why they burnt down, I know it is easy to blame the piston but in reality it is usually another reason other than the piston, like jetting, snow dust, antifreeze air leak etc.. -- Bill
 

·
Registered
Joined
·
969 Posts
got2ride said:
Ok - I know like many of you - I am anal when it comes to maintenance on my sled. Anyway - with a big trip to the Gaspe Peninsula in Feb - and a perceived loss of power from when it was new - I figured that I would have the dealer change the pistons and rings "just to be safe" Anyway - the compression prior to the change was 130psi. And after the new pistons/rings it was 130?? *%@? Anyway I had a lengthy discussion with my dealer as to why the compression did not increase after the installation of the new set. Blah blah blah.

During the X-mas New Year Break - traveled up to "THE HILL" for our annual family snowmobile vacation....anyway conditions actually were not that bad onto of the tug. As I was breaking a new set of pistons in - I was running about 50-1 pre-mix in the tank and being careful not to stress the motor - (I know my thoughts on breaking a box in) anyway at about 40 miles I fouled a plug - not to surprising as I was not traveling more than 35 miles an hour - (leading a group of 15 sleds). Changed plugs - fired right up but would not idle. Thought maybe bad gas..Who knows - decided to head the group back to the parking lot - goosed it up to 50 - 10 miles later - it just went dark. I mean it was like someone hit the kill switch. Went to pull it over and the re-coil broke. NOT A GOOD DAY.

Dropped the sled off at my dealer last Tuesday. He just called and explained that the right side (Mag?) was shot. Scored the cylinder - needs new one now.

So tell me - what the heck happened. The mechanics have been pouring over the sled trying to figure it out. They ruled out lubrication - oil pump test good and the pre-mix is obvious. No air leaks - base gasket in good shape no oil residue anywhere - coolant looks good...BTW they were Cudney's Pistons and Rings - absolutely not the problem in my book.

Any ideas - where can I point him.
[snapback]263975[/snapback]​
Incorrect installation would be my guess. Did they get all the antifreeze out of the bottom end? Did they make sure the ring didn't spin? And here is probably what really happened: Did they make sure there was no water or condensation in the fuel/tank? Bring the sled in cold to a warm service area and boom condensation happens. Use Iso in your tank when going from cold to warm and back to cold. I have been running those piston's for years now, never a problem. Also, mix a little oil in your first tank of fuel. Let's see a picture of the piston, can better tell.
 

·
RETIRED
Joined
·
11,148 Posts
Cudney Racing said:
I have seen the pistons on here in a couple of posts and they can generally be explained what happened to burn them down, we have sold over ten thousand pairs of pistons and there are some isolated cases of burn down, but when you see 2 or 3 of them posted it may sound like a lot but it is about .00015% of the total sold and of those all of them have a reason as to why they burnt down, I know it is easy to blame the piston but in reality it is usually another reason other than the piston, like jetting, snow dust, antifreeze air leak etc.. -- Bill
[snapback]264733[/snapback]​
thanks bill
that makes me feel much better!!!

scotty

btw, got the kit in the mail last week
cant wait till there in.....AND THERE'S SNOW!!!
 

·
Registered
Joined
·
14,289 Posts
FlipMode said:
but were we 0.0004" too tight
Do you mean .004" which is 4 thousands
or .0004" which is 4 tens of a thousands?

4 tens of a thousands is nothing to worry about, 4 thousands is.
[snapback]264728[/snapback]​
Nope.. I mean 4 ten thousands... if the minimum clearance spec was 0.005 with nominal of 0.0055 and max of 0.006 (and I am just picking numbers out of the air.. but they might be close) and the engine was assembled at 0.0046 clearance, this might be enough of a problem when you are first breaking it in.. running slightly lean and it is really cold out.. or very small air leak... Normally .. a tad under minimum probably wouldn't get you into trouble... but... if everything is stacking against you. And that may not have anything to do with this case. I just like to know my clearances when I assemble an engine.

Just like the jetting TT670 said is safe.. he also said you are doing it at your own risk and you need to watch what you are doing. He is a very knowledgeable guy.. and how do you think he got that way.. by reading and by experiencing. But he also assumes that your engine was correct.. no leaks.. no moisture (antifreeze or snowdust), proper clearances, the right amount of oil.. and not starting the sled and taking off when it is cold at max RPM to catch your buddy on the trail who started ahead of you.. Wonder why doo jets a little rich from the factory ( and they don't seem to be as rich as Polaris on base sleds). Maybe they have to be that way to protect themselves from the way we operate our sleds...and the conditions we might operate them in. It's just a thought.

Bill I was not maligning the pistons you were selling... as the failure rate is very very small and in most cases was probably do to a number of minor errors by the assmebliers or operators... Stuff happens. And people have to learn .. and sometimes (most times) the lessons are expensive...

It is very tough to call or pin point the exact reason for failure.. and there are usually more then one contributor.
 

·
Registered
Joined
·
3,816 Posts
I had the same problem with mine. Exactly the same. Same scoring intake and exhaust. More on the instake. Brand new cudney pistons and rings. 15 miles and I blew the PTO side. I'm putting the stock pistons back in with the 05 Chrome rings from DOO.
 

·
Registered
Joined
·
7,764 Posts
10 bucks says it was a reed cage gasket leak, or other air leak.

Other thing- A bout 3-4 mniles of break in isall that is needed... to bring to operating temp, make sure colant level s good. If you mix your tank about 60:1 you have no worries there........RIDE IT LIKE YOU STOLE IT, and you will have less problems.
 

·
Registered
Joined
·
7,764 Posts
ALSO, are you guys checking RING END GAPS?????

The cudney pistons come with rings that are to tight! They NEED to be filed!

I measured a set out to about .008" ring end gap.......ski-doo calls for.016"

I shoot for .015" and would settle for NO LESS than .013"
 

·
Registered
Joined
·
486 Posts
thats right ring gap is so important i checked my 670 H.O 's from wiseco and it was 0.016 on the bottom and 0.020 on the top
0.020 is needed for the top ring because it gets alot more heat
i bet theres no problems now

I had a set spi's with 100 miles the ring broke didnt check gap
 
1 - 20 of 30 Posts
Top