Snowmobile Fanatics banner

1 - 19 of 19 Posts

·
Registered
Joined
·
25 Posts
Discussion Starter · #1 ·
I was just wondering why I have only 100 psi on eack cylinder. I honed each, added new pistons, and rings. I have heard that it may take a while for the rings to wear to the cylinder, is this true? I only have about a half hour run time on the rebuild. Yes the motor was run 5 minutes prior to compresion check, and my gauge could be crap, it is an older one. It sure sounds like its running good, and feels like good compresion when I pull it over.
 

·
Registered
Joined
·
2,555 Posts
Yes it is true. Compression in a motor will build up after the break in process is complete. Im not sure how much psi your cylinders are stock but. Take it out for a drive, dont go past approx 80km/h but keep the throttle in different rpms after about 50 - 100kms
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #3 ·
James007 said:
Yes it is true. Compression in a motor will build up after the break in process is complete. Im not sure how much psi your cylinders are stock but. Take it out for a drive, dont go past approx 80km/h but keep the throttle in different rpms after about 50 - 100kms
Thanks man, That really makes me feel better to confirm that with someone. I had about 25 hours into the motor work last weekend, and the last thing I need is to be second guessing my work.
 

·
Registered
Joined
·
1,458 Posts
Might need a little more run time for the rings to seat fully, but you should have just about all the compression youre going too. Did you hold the throttle wide open and pull till the needle stopped going up on the gauge? Like you said, gauge could be crap too. Best bet would be to run a full tank of fuel through it, utilizing your desired break in process, and recheck compression with another gauge if possible.

Good luck man[thumb]
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #5 ·
Luke said:
Might need a little more run time for the rings to seat fully, but you should have just about all the compression youre going too. Did you hold the throttle wide open and pull till the needle stopped going up on the gauge? Like you said, gauge could be crap too. Best bet would be to run a full tank of fuel through it, utilizing your desired break in process, and recheck compression with another gauge if possible.

Good luck man[thumb]
Yes I tried to hold the throttle wide open and pull hard but those 900s are a pretty tough pull even with the plugs out with one hand. I will have a new compresion tester this next paycheck. Man I have rebuilt this thing twice in the last 2 weeks and have only had it 3 weeks. This second time I really dug deep, pulled motor, split case, bought another good case and crank, , spent $900, but I think I have almost that left in good left over parts. Snows in the forcast in Wisconsin.[:)]
 

·
Registered
Joined
·
1,458 Posts
Thunder1 said:
Luke said:
Might need a little more run time for the rings to seat fully, but you should have just about all the compression youre going too. Did you hold the throttle wide open and pull till the needle stopped going up on the gauge? Like you said, gauge could be crap too. Best bet would be to run a full tank of fuel through it, utilizing your desired break in process, and recheck compression with another gauge if possible.

Good luck man[thumb]
Yes I tried to hold the throttle wide open and pull hard but those 900s are a pretty tough pull even with the plugs out with one hand. I will have a new compresion tester this next paycheck. Man I have rebuilt this thing twice in the last 2 weeks and have only had it 3 weeks. This second time I really dug deep, pulled motor, split case, bought another good case and crank, , spent $900, but I think I have almost that left in good left over parts. Snows in the forcast in Wisconsin.[:)]
Twice? What happened the first time around?

Can you rent a compression testor from a parts store? Then you can compare it to the one you already have to either confirm or disprove your previous reading without dropping any more cash that you might not need to.

Tape the throttle open[thumb]
 

·
Registered
Joined
·
2,555 Posts
You can also buy cans of compression when its low, its a can with a sparkplug like end that threads into your cylinder and sprays.
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #8 ·
Luke said:
Thunder1 said:
Luke said:
Might need a little more run time for the rings to seat fully, but you should have just about all the compression youre going too. Did you hold the throttle wide open and pull till the needle stopped going up on the gauge? Like you said, gauge could be crap too. Best bet would be to run a full tank of fuel through it, utilizing your desired break in process, and recheck compression with another gauge if possible.

Good luck man[thumb]
Yes I tried to hold the throttle wide open and pull hard but those 900s are a pretty tough pull even with the plugs out with one hand. I will have a new compresion tester this next paycheck. Man I have rebuilt this thing twice in the last 2 weeks and have only had it 3 weeks. This second time I really dug deep, pulled motor, split case, bought another good case and crank, , spent $900, but I think I have almost that left in good left over parts. Snows in the forcast in Wisconsin.[:)]
Twice? What happened the first time around?

Can you rent a compression testor from a parts store? Then you can compare it to the one you already have to either confirm or disprove your previous reading without dropping any more cash that you might not need to.

Tape the throttle open[thumb]
I bought it on a staurday, sunday I took It to the lake, went three miles and it locked up on the pto side cylinder, monday I orderd parts, tuesday I rebuilt it, cleaned carbs, and wednesday I took it back out to the lake. I went a couple hundred yards, checked plugs, pto cylinder plug was white so I turned around and slowly headed towards the truck and she locked up again. This time the cylinder had cracked and ring snaged and demolished piston and rings. To make matters worse, I put the hood up and the cable broke and hood floped way forward, luckily not damaging hood. I was really on the fence on parting it out, but with only 3200 miles and a good friend I was persuaded into rebuilding again but not untill we found the real problem. Turns out the case had a hairline crack so I found another case, with all good parts, and picked it up for $500. Now I believe it is running top notch, and I have about $1000 in exta parts. I took it out yesterday for a nice 30 to 50 mph ride and it got hot, turns out I didnt get all the air out of the cooling system. I now have it completly full of water, no air, and shes ready for another test ride. I am scared to death to try it again for another let down, but it sounds nice and tight, and really purs. I run it in the garage for 10 minutes and alls good, stays cool. I must note that the first day I took it out it had so much power is was unbelievable, so I had to keep it just to experiance the power again. Wish me luck guys, and thats the hole story of my last 3 weeks. Sorry so long winded.


James007 said:
You can also buy cans of compression when its low, its a can with a sparkplug like end that threads into your cylinder and sprays.
I will take three, lol
 

·
Registered
Joined
·
1,458 Posts
Wow, you just bought it and you already have some history with it, lol. I rebuilt my top end after a good burndown this year, too. I was nervous as hell when I got it back out on the lake after she was broke in, but I took the necessary steps to make sure it didnt happen again. Sounds like you did the same, im sure itll be fine.

When you said in your first post that it had 35 min run time. How much of that was driving time and how much was idling time? The drive time is what really seats the rings. If you only have 10 min or so drive time then you prob could expect to gain quite a bit more comp after the 1/2 hr - 1 hr runtime. In my first reply I was thinkning you were talking about 35 min of driving time.
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #11 ·
James007 said:
I am going to try to add some new pics of my 96 t-cat 2 my gallery rite now, if I can figure out how to add a pic to my posts like you guys got I will. Thanks
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #12 ·
Luke said:
Wow, you just bought it and you already have some history with it, lol. I rebuilt my top end after a good burndown this year, too. I was nervous as hell when I got it back out on the lake after she was broke in, but I took the necessary steps to make sure it didnt happen again. Sounds like you did the same, im sure itll be fine.

When you said in your first post that it had 35 min run time. How much of that was driving time and how much was idling time? The drive time is what really seats the rings. If you only have 10 min or so drive time then you prob could expect to gain quite a bit more comp after the 1/2 hr - 1 hr runtime. In my first reply I was thinkning you were talking about 35 min of driving time.
Good point. I really only have about 15 minutes drive time on the sled as of now, and currently 100 psi per cylinder, at least I have consistant pressure going for me. I should have never even checked it, It sounds mean, and runs great, just have to get her back out to the lake tomarrow after work, maybe I will try a different lake for better luck, lol. How many miles were on your sled when she burned down?
 

·
Registered
Joined
·
1,458 Posts
[/quote]

I am going to try to add some new pics of my 96 t-cat 2 my gallery rite now, if I can figure out how to add a pic to my posts like you guys got I will. Thanks
[/quote]

You need to upload your photos to an image hosting website like photobucket. Photobucket will give you a direct link to each pic and then you copy and paste the link between the brackets that you get click on the "insert image" button from the little toolbar above the text box for replying to a thread. If you upload them to SF then to insert them into a thread all you have to do is click on the little paperclip when replying to a thread and itll bring you right to your gallery and you can link them to a thread from there.
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #14 ·
I am going to try to add some new pics of my 96 t-cat 2 my gallery rite now, if I can figure out how to add a pic to my posts like you guys got I will. Thanks
[/quote]

You need to upload your photos to an image hosting website like photobucket. Photobucket will give you a direct link to each pic and then you copy and paste the link between the brackets that you get click on the "insert image" button from the little toolbar above the text box for replying to a thread. If you upload them to SF then to insert them into a thread all you have to do is click on the little paperclip when replying to a thread and itll bring you right to your gallery and you can link them to a thread from there.


[/quote]
Ok, great, I added some. So if you click on my name Thunder1 name you can see the trouble maker, and a couple others I had in the past. Now to put my pic by my screen name do I add the one I want to the avatar box?
 

·
Registered
Joined
·
1,458 Posts
Thunder1 said:
Luke said:
Wow, you just bought it and you already have some history with it, lol. I rebuilt my top end after a good burndown this year, too. I was nervous as hell when I got it back out on the lake after she was broke in, but I took the necessary steps to make sure it didnt happen again. Sounds like you did the same, im sure itll be fine.

When you said in your first post that it had 35 min run time. How much of that was driving time and how much was idling time? The drive time is what really seats the rings. If you only have 10 min or so drive time then you prob could expect to gain quite a bit more comp after the 1/2 hr - 1 hr runtime. In my first reply I was thinkning you were talking about 35 min of driving time.
Good point. I really only have about 15 minutes drive time on the sled as of now, and currently 100 psi per cylinder, at least I have consistant pressure going for me. I should have never even checked it, It sounds mean, and runs great, just have to get her back out to the lake tomarrow after work, maybe I will try a different lake for better luck, lol. How many miles were on your sled when she burned down?
Lol, I did the same thing when mine blew. I checked it before I ran in, after 10 min idling, after half a tank, after a full tank. The readings got progressively better, now Im up to 130 pto and 125 mag. My sled has 9200+ mi on chassis, 4000+ mi on bottom end, 1200+ on last top end rebuild (new pto jug and piston due to cracked port). Im pretty sure Ethanol, wide open throttle, and borderline lean conditions were to blame since I was jetted for non ethanol fuel and I didnt even think about the different fuel at the time. We were drag racing and I just blew the doors off a 900 fusion,........then I blew a piston less than a mile later[:(] which also took out the jug. I jetted up the mains and needles just in case and bought new carb boots.

But I got her all back together with a few hundred miles on her. Lined up against my brothers 03 F7. He got me once and I got him once, very close race. He has studs, offset keyway, Bikeman y-pipe, and can. Not to bad for a 12 year old sled to hold its own to an F7, eh?[:D]

Just checked you gallery, very nice kitty you got there. Very clean looking, def worth holding onto as long as she treats you good from here on out. Dont see many of those anymore that are still that nice.[thumb]
Anyway, just stay away from wide open throttle for 100 miles or so, and dont hold a constant speed. Give it some here and there with some quick little throttle pulls but thats about it.

Im sure shell be fine now. Good luck[thumb]
 

·
Registered
Joined
·
25 Posts
Discussion Starter · #17 ·
Luke said:
Thunder1 said:
Luke said:
Wow, you just bought it and you already have some history with it, lol. I rebuilt my top end after a good burndown this year, too. I was nervous as hell when I got it back out on the lake after she was broke in, but I took the necessary steps to make sure it didnt happen again. Sounds like you did the same, im sure itll be fine.

When you said in your first post that it had 35 min run time. How much of that was driving time and how much was idling time? The drive time is what really seats the rings. If you only have 10 min or so drive time then you prob could expect to gain quite a bit more comp after the 1/2 hr - 1 hr runtime. In my first reply I was thinkning you were talking about 35 min of driving time.
Good point. I really only have about 15 minutes drive time on the sled as of now, and currently 100 psi per cylinder, at least I have consistant pressure going for me. I should have never even checked it, It sounds mean, and runs great, just have to get her back out to the lake tomarrow after work, maybe I will try a different lake for better luck, lol. How many miles were on your sled when she burned down?
Lol, I did the same thing when mine blew. I checked it before I ran in, after 10 min idling, after half a tank, after a full tank. The readings got progressively better, now Im up to 130 pto and 125 mag. My sled has 9200+ mi on chassis, 4000+ mi on bottom end, 1200+ on last top end rebuild (new pto jug and piston due to cracked port). Im pretty sure Ethanol, wide open throttle, and borderline lean conditions were to blame since I was jetted for non ethanol fuel and I didnt even think about the different fuel at the time. We were drag racing and I just blew the doors off a 900 fusion,........then I blew a piston less than a mile later[:(] which also took out the jug. I jetted up the mains and needles just in case and bought new carb boots.

But I got her all back together with a few hundred miles on her. Lined up against my brothers 03 F7. He got me once and I got him once, very close race. He has studs, offset keyway, Bikeman y-pipe, and can. Not to bad for a 12 year old sled to hold its own to an F7, eh?[:D]

Just checked you gallery, very nice kitty you got there. Very clean looking, def worth holding onto as long as she treats you good from here on out. Dont see many of those anymore that are still that nice.[thumb]
Anyway, just stay away from wide open throttle for 100 miles or so, and dont hold a constant speed. Give it some here and there with some quick little throttle pulls but thats about it.

Im sure shell be fine now. Good luck[thumb]
UPDATE, Thanks for all the advice. I just got home from the lake and the thundercat run AWSOME!!! It was really hard to ride it slowly for the break in. I did what you said and varied the throttle below 60 mph for about an hour. I finally had 50 miles on it so I headed out towards the middle of the lake and stoped. I steped toward the back of of the running boards and squeezed the throttle all the way in and she stood rite up and hung there for about 100 yrds. I cruised at 60 mph on hard pack and nailed it. The damb skis were hardly touching the ground and she shot up past 100 mph in what seemed like 2 seconds. I let off and rode the last half hour nice and gradual again till I loaded it up. Man I am so happy. It was totally worth all the time and money. I cant wait to get it out again this weekend. P.S., I even talked the D.N.R. guy into helping load it up when I left. LOL
 

·
Registered
Joined
·
15 Posts
I did a zoom in on your picture of your engine, and it appears you will be needing a new chain soon, just like I do. Your tensioner, like mine, is screwed in all the way. I would plan on putting a new chain on soon, by next season at the latest. I'm changing mine this summer. All that power is addictive, but hard on the chain. Just my 2 cents.
 

·
Registered
Joined
·
3 Posts
I have a '96 thundercat too and had done a top-end rebuild over the summer. I had the same concern when finished about the compression. After a break in period, a tank full of mixed fuel and easy on the throttle, I'm runnig about 140 psi on all three, runs strong. I love these triples.
 
1 - 19 of 19 Posts
Top