I read a past post that mentioned testing rings by performing a leak down test. Could become a summer thing to do. so let's list the steps and what is needed. Also at what percentage of leakdown do you change rings or what ever else is nessecary?
Oldman, first you will need a leak down tester, snap-on has a nice one, also saw one in the summit racing catalog for $70.00. I have the snap-on , to doo a leak down test first you will have to remove spark plugs, bring cly to test to t.d.c.
screw adaptor hose in to spark plug hole, hook tester to air supply(you need a compressor) zero tester gage then hook to adaptor hose you wiil get a reading of the percentige of air leaking past the rings.
2-3 % is perfect. Anything over 10-15 % and I would be tearing it apart for a inspection. It will show a cly or piston ring problem way before a compresion tester will.
A compression test does not tell you the condition of the rings for example oil will help seal the rings, if the motor is hot or cold will give you different compression, the best way to check the condition of the rings is a leakdown test. Like Mr 670 said 2 to 3% is good and 10 t0 15% rings should be changed, we change rings in our race sleds as soon as the 2 or 3% doubles for instance at 6% we ring them, however because of the single ring in a Ski Doo twin and the piston to wall clearance we find the typical leakdown of most motors around 15% or so when brand new and when you leakdown approx 25 to 30% in these engines you should at least rering them. Quite typically these motors will leak down more than 30% within 500 to 1000 miles on the engine. -- Bill
TB2 is correct about one thing and that is once you install the L ring and rail ring piston and set the right squish the motors not only run better they also make more power, we have sold a lot of 700 pistons which we have made which have moly coated pistons with ceramic tops and an L ring and a rail ring and they make a remarkable difference in any 700 they are installed in. Even though a lot of people think there sled is running good just the way the are, if you have more than 1000 miles on your sled a very noticeable difference is made by installing new pistons and rings. -- Bill
I can see you installing rings ay 1000 miles if you want to stay on edge.....but why are pistons needed??......As a rule I was told to rering at 4000 miles because of fatigue.... Better safe than sorry because its cheaper to re ring than it is to fix the damage caused by a broken ring.....ie..bittom end and a jug....
I leaked down my 98 mxz 500 just a month or two ago and it is almost the same as when i bought it new. It still perfoms the same and holds with 2000 500mxz.
Are the old rotary engines just built better. I seem to remember they were more expencive to make. Ive torn open a few engines but i never needed to open a rotory valved engine so i dont know what they look like inside.
Even in a compression test its still 151 exactly on both sides and it was 151 the first month i bought it using the same gauge. Now it almost has 10000km on it.
</span><table border="0" align="center" width="95%" cellpadding="3" cellspacing="1"><tr><td>Quote (bobber @ Mar. 27, 2002, 06:48am)</td></tr><tr><td id="QUOTE">Belleville what kind of oil do you use and how much? Has the machine been ever overheared? These are just a couple of things that affect your rings.[/b][/quote]
The guy that had it before me used Bombi syn for about 2/3rds of the 5 k he put on it, and I use torco. No its never been cooked, and it runs real strong.
I would like to know if the 500 to 1000 mile ring/piston change applies to the nikasil cylinders as well. I tore my 01 mxz 800 down to send the cylinders of to be ported when it had 800 miles on it and it looked and tested as brand new, compression and leak down checked before and after. It only stands to reason that performance is lost with use of the sled but i personally think the amount is very slight if the right oil,gas, and start up procedueres are demonstrated at least within 5000 miles.
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