I guess this is hard to pick a number that works for everyone.
My personal feeling is don't expect great performance without great low leak down numbers.
0 to 2.5 great
2.6 to 5.0 fair
5.1 to 7.5 not good
7.6 and above bad
Dan
LeakDown results- post em up
- Thread starter minus40
- Start date
I guess this is hard to pick a number that works for everyone.
My personal feeling is don't expect great performance without great low leak down numbers.
0 to 2.5 great
2.6 to 5.0 fair
5.1 to 7.5 not good
7.6 and above bad
Dan
With the changes to the 2020 Polaris 850, I'm not expecting any problems however I always do a baseline on all my sleds at the beginning of the season. Anyone else do baselines leak down, compression and follow up tests? For those of you that plan some engine mods (or new to motor mods), examples: single, or twin pipes, heads, big bore, turbos etc I would recommend putting some break in miles first. I know many of you semi pro builders know enough about your motors to just mod them from day one. Hoping everyone has a great year on the snow!!
B
I have an SLP leak down tester that only has one gauge. The instructions show quite different results than what's posted here & testing on a couple of used decent running engines also show higher numbers [14 & 18%] Is it just the type of gauge I have? What brand is everyone else using?
The following was taken from the SLP Leak Down Tester instruction sheet:
Cylinder leakage on a new engine or good condition cylinder walls and piston rings should be
within the 5% to 15% range and is best for power. Good service from the engine can be as much
as 25% for average use. Over 25% would be recommended to install new rings and pistons if
needed. Check cylinder for excess clearance, out of round or taper, repair as needed.
When you get above 5%, it’s a very noticeable change in performance. 2g weight change will not regain consistent rpm. Torque drops off big time at 5% and you will start chasing clutching without improvement. At 9% your 850 feels like a 550.
B
Thanks, I get all of that & I agree. But my tester is a single gauge tester and I believe it's operating at a lower pressure which might be changing the acceptable percentages. I'm hoping that someone experienced with a single gauge tester can confirm that & give some more definitive percentages for that particular type of tester. If not, I'll upgrade to a twin gauge in order to have comparable percentages with everyone else. I'm looking at the OTC tester, any recommendations?
I have a OTC and it works great. Could you post a picture of the single gauge tester that you have? Just wondering if there would be a way to add a pressure gauge to it.
B
Good to see people getting involved with leak down testing.
As far as numbers go ....and different tester.
The numbers I thru our we're a bit Radom and when I say that I meant exactly that. ( many here bring up good points ) suck as same tester ? What air pressure ? Cold motor , warm motor ? Hot motor ? New sled ? 250 miles , 500 miles, 750 miles 1000 miles.
Let's simplify this....
as far as tester go, we mainly use 2 different ones, ( and we and we constantly cross check them against each other. ( and someone brought up to buy the one that Indydan uses. ). Well here is where I need to explain.
We use an OTC, and a Snap on ...... Then we randomly test the import ones we sell... The import ones have been brought into offer a cheap price which was kinda stupid because they are a little random. ( but we are going to bring in only the OTC Dual gauge one. ) and stick with that. )
But let's just say we have to work with numbers from all different gauges so we can be real about all this.
Trouble shooting two stroke performance motors...... Is complex and if you are infatuated with peak performance then you should leak down test your new sled before you drive it.
Then at 250, 500, 750, 1000, 1500, 2000 and so on ( ball park of thes numbers. )
All that really matters is that either they stay very close to the same with little change from new..
Or...... The test starts out a little on th bad Side because of sub-par cylinder roundness or a below average set of rings ..... Let say 6 percent and the numbers keep getting better as it breaks in let say down to 1-1/2% to 3% and then stabilizes and flattened off.
No mater what guage, what pressure, or what technique if the numbers start to go up the need for a rebuild is coming. Soon
And here is the most important part of of all..... If the pull on the recoil rope starts to get harder and harder over time the motor on its way out.
Why does this happen you ask ? ( trust me your compression test numbers will not being going up..... ) but your leak down numbers will be going up.
What is happening is your rings and or Pistons ( most often both ) are failing and the hard pull on the rope comes from and pressure is going past the rings and pressurizing the crankcase and the motor starts fighting itself so to speak.
Don't be fooled by a great ring seal that is a crisp distinctive snap of the piston going over TDC ...... With great seperation .
Verses a poor overall hard pull that just feels ****ty and both cylinders kinda feel somewhat rolled together that lacks separation.
Leak down is the single best ( Motor ) performance trouble shooting test ( period )
Not, clutching and fuel mapping test.
I hope this helps.
Dan
As far as numbers go ....and different tester.
The numbers I thru our we're a bit Radom and when I say that I meant exactly that. ( many here bring up good points ) suck as same tester ? What air pressure ? Cold motor , warm motor ? Hot motor ? New sled ? 250 miles , 500 miles, 750 miles 1000 miles.
Let's simplify this....
as far as tester go, we mainly use 2 different ones, ( and we and we constantly cross check them against each other. ( and someone brought up to buy the one that Indydan uses. ). Well here is where I need to explain.
We use an OTC, and a Snap on ...... Then we randomly test the import ones we sell... The import ones have been brought into offer a cheap price which was kinda stupid because they are a little random. ( but we are going to bring in only the OTC Dual gauge one. ) and stick with that. )
But let's just say we have to work with numbers from all different gauges so we can be real about all this.
Trouble shooting two stroke performance motors...... Is complex and if you are infatuated with peak performance then you should leak down test your new sled before you drive it.
Then at 250, 500, 750, 1000, 1500, 2000 and so on ( ball park of thes numbers. )
All that really matters is that either they stay very close to the same with little change from new..
Or...... The test starts out a little on th bad Side because of sub-par cylinder roundness or a below average set of rings ..... Let say 6 percent and the numbers keep getting better as it breaks in let say down to 1-1/2% to 3% and then stabilizes and flattened off.
No mater what guage, what pressure, or what technique if the numbers start to go up the need for a rebuild is coming. Soon
And here is the most important part of of all..... If the pull on the recoil rope starts to get harder and harder over time the motor on its way out.
Why does this happen you ask ? ( trust me your compression test numbers will not being going up..... ) but your leak down numbers will be going up.
What is happening is your rings and or Pistons ( most often both ) are failing and the hard pull on the rope comes from and pressure is going past the rings and pressurizing the crankcase and the motor starts fighting itself so to speak.
Don't be fooled by a great ring seal that is a crisp distinctive snap of the piston going over TDC ...... With great seperation .
Verses a poor overall hard pull that just feels ****ty and both cylinders kinda feel somewhat rolled together that lacks separation.
Leak down is the single best ( Motor ) performance trouble shooting test ( period )
Not, clutching and fuel mapping test.
I hope this helps.
Dan
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B
I couldn't find any testers on your website. How much is the OTC?
I bought an OTC dual gauge tester off Summit Racing for $80; would be a great bargain if it were the same quality as old school OTC tools, but it's China stuff. Probably better than a no-name off Amazon, but still, I suspect it shows a bit more leakdown than it should. Unfortunately, I don't have another gauge to check it against. Seems like there's quite a bit of variation between cheap testers, probably even from unit to unit from the same manufacturer. Given that, it's probably best to use your gauge to check several known good motors and make the highest reading you see your baseline. https://www.hotrod.com/articles/hrdp-1203-budget-leakdown-testers-tested/
V
I'll play.
2020 800 Axys ~400 miles as I didn't fire the sled up to confirm.
Cold engine and didn't spin it over so rings are likely dry as it hasn't run since last Saturday.
I made a piston holding tool out of an old spark plug, welded a 3/8" nut on it so the 3/8" redi-rod would thread thru. Rounded the business end of the rod and affixed an indexing washer on the other end to watch rotation of the rod to allow piston travel once in operation.
Piston determined to be BDC with threaded plunger and install OTC dual gauge leak down tester that is not confirmed to be accurate but will be consistently used over time on the same engine.
At TDC of the tested piston I'm showing 2-3# of pressure drop. I released the pressure hose and turned the rod out 1 rotation and reattached the pressure hose to the gauge. I could hear the air passing the rings and saw about 10# of pressure loss. This happened on both holes.
I'm open to comments about cold engine, warm engine, oil in cylinders, etc. I was actually interested to see how far down the bore the piston would travel before the pressure showed a significant drop. Just one turn of the redi-rod kind of surprised me so I thought I would wait for a response before I continued on with the experiment. I also neglected to do a compression test on this engine, next time.
2020 800 Axys ~400 miles as I didn't fire the sled up to confirm.
Cold engine and didn't spin it over so rings are likely dry as it hasn't run since last Saturday.
I made a piston holding tool out of an old spark plug, welded a 3/8" nut on it so the 3/8" redi-rod would thread thru. Rounded the business end of the rod and affixed an indexing washer on the other end to watch rotation of the rod to allow piston travel once in operation.
Piston determined to be BDC with threaded plunger and install OTC dual gauge leak down tester that is not confirmed to be accurate but will be consistently used over time on the same engine.
At TDC of the tested piston I'm showing 2-3# of pressure drop. I released the pressure hose and turned the rod out 1 rotation and reattached the pressure hose to the gauge. I could hear the air passing the rings and saw about 10# of pressure loss. This happened on both holes.
I'm open to comments about cold engine, warm engine, oil in cylinders, etc. I was actually interested to see how far down the bore the piston would travel before the pressure showed a significant drop. Just one turn of the redi-rod kind of surprised me so I thought I would wait for a response before I continued on with the experiment. I also neglected to do a compression test on this engine, next time.
HOLD ON AND DON’T DO ANYTHING YET !
never mind I paniced when you said piston stop and I didn’t see the adjustable long stop.
I have seen people break pistons if the piston has a run at the stop.
carry-on
I like room temp 70 degrees or a warmer motor.
11% is not so great with 400 miles…. I would ride it another 400 and chk again…. if it gets better ok
if it gets worse, I would pull it down and get the cylinder honed correctly.
Then I would re-ring it or put piston kits in if the skirts are worn
never mind I paniced when you said piston stop and I didn’t see the adjustable long stop.
I have seen people break pistons if the piston has a run at the stop.
carry-on
I like room temp 70 degrees or a warmer motor.
11% is not so great with 400 miles…. I would ride it another 400 and chk again…. if it gets better ok
if it gets worse, I would pull it down and get the cylinder honed correctly.
Then I would re-ring it or put piston kits in if the skirts are worn
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Dan
Can you post a video of you performing a leak down test so everyone knows the proper procedure for doing it? That would really clarify the process and I'm sure it would be appreciated.
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