When is it time for a rebuild?

Great info, that's what I like about yammie guys, they are always willing to share their opinion. A couple of more questions though......everyone's talked about the top end but what about the bottom end, when does it need to be looked at and what typically needs to be done? Also opinions about aftermarket pistons.... Weisco, stock, or OEM spec brand, what does a non-race motor need? I know the Weisco's are forged and cost about a hun, stock are a little cheaper, and brand three about 50 bucks. What would you buy? Also when doing a leak down test, what position in the cylinder should the piston be in?
 

When you guys mention a leak down test, how much different is it than just checking compression? Do you leave the tester on the cylinder for a certain period of time and then measure your loss?
 
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@snow guy,

as fare as i know bottoms don't need any maintenance maybe seals if ya
got the top off.

as fare as pistons go OEM all the way!!!..

doing a leak down test your piston should be at TDC and charged with
100psi, i do a LDT every 2-3 years.

@SRXtrafast,

doing a LDT checks to see how good of condition your whole piston is(tightness in the boar),also checks other things too,on a 4stroker ,valves


there's more to it but that's a fast lowdown.

you attach a set of gauges with a regulator and with shop air pump 100psi
into your cyl. and then look at the other gauge to see how much of that
100psi your holding, you don't want any more that 10% leak down.

so if you can hold at least 90psi your ok.

others will be in with more info i'm shure.:)
 
wait untill you break it in before putting in the synthetic oil. yamiman had a problem with his sxr700 last year. put synth in too early and sled ran like crap.
 
I'm on the fix it before it breaks program....will be pulling both my srx's apart. I'd rather fix them now than have it break on a trip.
 
I did a compression check and both cylinders came up with about 110 after the 3rd pull. When I did the leak down test I could only get in about 20psi then the engine would rotate, is there some trick to keep it from doing this?
 
simply inset a wooden rod or hammer handle or whatever thru the primary clutch and wedge it with blocks of wood on each side to the belly pan with the cylinder your going to check at TDC.
 
Any tips on finding TDC, I put my finger over the plug hole and wait for the compression stroke, is there a better way? Also is there any danger of blowing out any seals when putting 100psi in? I know when testing my 4 wheeler it said not to go over 20psi as it would blow out the crank seals.
 
snow guy said:
Any tips on finding TDC, I put my finger over the plug hole and wait for the compression stroke, is there a better way? Also is there any danger of blowing out any seals when putting 100psi in? I know when testing my 4 wheeler it said not to go over 20psi as it would blow out the crank seals.
Click to expand...

use a flash light and look down the cyl.

i've used 100psi many times no problems,all that psi don't transfer all to the
crankcase some does but most stays in the cyl..
 
got 5580 miles on my monster, Still kicking,starts good and runs good. If it makes it thru this season until spring,I will replace piston and rings next summer. :o|
 
Can someone do a write up in the Tech section on how to replace your pistons and rings..etc. with step by step pics.Info on what to look for and things to look for as you are doing the procedure. This would help many of us TY'ers who have'nt done the replacement yet. Give some tips and the correct way to do it. :winterrul
 
snow guy said:
Any tips on finding TDC, I put my finger over the plug hole and wait for the compression stroke, is there a better way? Also is there any danger of blowing out any seals when putting 100psi in? I know when testing my 4 wheeler it said not to go over 20psi as it would blow out the crank seals.
Click to expand...
There are 2 different types of leakdown tests . . .
  1. Cylinder leakdown to test the pistons, rings, and cylinder wall seal. This test uses a higher pressure such as 100psi.
  2. Crankcase leakdown test is used to check for any air leaks in the whole case, or the seals. All ports are sealed off with plates and gasket material (intake, exhaust, exhaust valve, etc.). This test only uses about 10 or 15 psi. This test is very useful to finds out if the cases were leaking after a burndown.
I am guessing that your 4 wheeler manual was referring to the latter type.
 
mrviper700 said:
See,... theres people who will run them till they break, then they know they need something done because it went boom, or you can keep them fresh. Sorry, but rings and pistons in a 2 stroke snowmobile of any brand will not be within spec at 11,000 miles no matter what oil you run!! It may still run fine to you the same owner of it since new, I dont argue that, these yamahas are great about giving you trouble free service but its not running the way it did when it was new! I would be willing to bet you the sides of your pistons were very dark brown and black all the way to the bottom of the side of the skirt, this is blow by!! this cant be done with a compression tester, see you can build compression, but how long can you hold onto the compression is the real task in a 2 stroke.

I fixed a srx last year that was the cleanest sled you could ever possibly find, I think the guy kept it in his living room..., anyways, at 6600 miles all 3 pistons were way under spec, yamalube used its whole life. Sure it started and ran fine, but it wasnt making all the power it used to!! The thing is if it would have had the piston rings changed just 1 time in the 6600 miles, it wouldnt have gotten to the point of letting the piston rock back and forth and wear the skirt from instability. The stock yamaha srx/viper pistons are about the best out there, a powder forged unit that runs a nice tight skirt to wall clearance, this improves sealing and stability, but once the rings get tired, it lets it rock back and forth and this leads to skirt wear and blowby. I dont think people understand what it is that drives a 2 stroke engine, its the piston/rings!! Theres no camshaft, valves, oilpump,etc. Ring seal and piston stability is crucial in a 2 stroke, its how all the power is moved around in the engine, and it is what the deciding factor is on how quickly and efficently it can be moved, sloppy rings and pistons contaminate the fresh fuel/air mix in the crankcase with burnt fuel/air charge that seeps by the rings into the crankcase below instead of being evacuated out of the engine, this in turn heats up your fresh mixture and this makes less power. heat is the number one enemy of a 2 stroke sled, the warmer the engine, the richer it is, the power drops off!

The reason there isnt 2 stroke cars out there is because although a 2 stroke engine makes more power then a 4 stroke does with less weight, it cant be made to give suitable service life without piston /ring service!!

Like I said, some people will run them till they break, thats fine its a free world, you have to make your own decisions, but if you want your machine to stay in tip top running shape, you cant ignore the rings and pistons...its like not ever changing the oil in your car till 50,000 miles! sure it will run fine, but its not going to make the power it should from the contaminates in the oil which in turn effect the way the engine makes power overall. Its your engine and what and how you maintain it is entirely up to you, I am just trying to explain why you should maintain it, at least you have the facts and other differning opinions...........what you do is your decision.
Click to expand...

I believe that was my 02 SRX that Don is talking about that he tore down last year with 6600 miles on it when i got it. I was there when we tore it down and im telling you guys, the top end was cooked!! Black piston crowns and worn cylinder plating from worn piston rings causing piston to slop in the cylinder. Wrist pins were Blue and wrist pins bearings were like charcoal!!! PLEASE do yourselfs a favor and change your rings every 2,500 - 3,000 miles and run amsoil or Klotz
 
Well I just did a leak down test and both cylinders tested out at about 5% leakage at 100 psi, not bad for a motor with 5K on it. Now my next question what do I have to gain by tearing the engine down and re-ringing it? Peace of mind? I'm thinking the leak down numbers won't get any better than they are now so why mess with it?
 
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