Pro rebuild question

Careful that you don't mis-interperet what a "full warmup" is. We're dealing with 2-stroke engines here. They prefer not to 'idle'. Bad things can happen with oiling and fouling when you let a 2-stroke idle for a long time. Idle from cold for just a couple of minutes. Get it to about 80 or 90 and then drive easy till it gets to 120. Then go crazy. If you let it sit and idle for like 5 minutes, you'll probably need to rebuild it again sooner than you'd like...

tuneman said:

Careful that you don't mis-interperet what a "full warmup" is. We're dealing with 2-stroke engines here. They prefer not to 'idle'. Bad things can happen with oiling and fouling when you let a 2-stroke idle for a long time. Idle from cold for just a couple of minutes. Get it to about 80 or 90 and then drive easy till it gets to 120. Then go crazy. If you let it sit and idle for like 5 minutes, you'll probably need to rebuild it again sooner than you'd like...

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It gets super cold here and some days (my sled is usually outside) a 5 minute idle for my sled will still have the engine temp at -20 or -15c lol. 8000km on my pro with the stock motor. I always let it warm up to 25-30c before moving it but some times that takes 20 minutes

rowe said:

It gets super cold here and some days (my sled is usually outside) a 5 minute idle for my sled will still have the engine temp at -20 or -15c lol. 8000km on my pro with the stock motor. I always let it warm up to 25-30c before moving it but some times that takes 20 minutes

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I'm on board with you. It's not a time thing. It's 'what's the water temp'. All of my sleds have had a water temp gauge. Either factory or aftermarket. My sleds do not move until they reach 90 degrees on a second warm up. I always start the sleds, let them warm up to 90, shut them down. Get my gear on, warm up to 90 again and putz down the trail until it hits about 115. Never an issue with motor or valves. But some oil will gum up valves quicker than others. To each their own on oil.

Now back on topic for a fresh rebuild. Some will probably disagree here. I've always done 3 garage/stand break-ins (heat cycles) for the new rings/Pistons. I usually shut it down at 100 in the garage, the engine will accumulate more heat even after its shut down. Don't want to over heat it. Let it sit for a few hours and do the next cycle and so on. I'll be doing this to my new Axys as well.

Do a few heat cycles like longhorn said, let the sled warmup before taking off down the trail, fluctuate the throttle often, open it up for a few seconds here and there, and keep an eye on the antifreeze.

http://www.mototuneusa.com/thanx.htm

The real deal.

Pretty hard to screw up a piston-ring R&R today as long as the fit of both is correct as well as your piston pick and their ring material(another subject). But it's still pretty easy to screw up the break-in

Adding a little extra oil (beyond what you have been using) with oil pump and fuel mix
helps ring seal until the rings take a seat. Better ring seal from the get-go will help the final seal %. This takes longer that some might think with today's hardcoated cylinders if the initial bore is being re-rung.
IMO a minimum of 5 tanks or rides of extra oil after a re-ring with a deglazed nikasil cylinder would not be too much. No deglaze,,, maybe much longer.
Even a rigid hone only touches the high spots but it is the low spots that have lost the most cross hatch (what cuts the ring to shape).

Doing a few heat cycles may help stabilize piston construction and relieve some structural stresses. I don't know for sure about today (haven't seen high spots on pistons for a long time) but it was very important in the old days so i still do it today for peace of mind. It's never caused poor ring seal for me.

The above posts on how you warm up are important IMO. Not just for new pistons but for "ol' buddy" motors too. The tighter clearance from new pistons just makes the wrong things show up quicker.
You have to be aware of bringing the coolant temp up before load for clearances but it is more important IMO to be aware of how much oil is available to your motor. A 2 stroke needs a puddle in the crankcase. Pretty random but it is what it is.

The electric oil pump will help a lot (keeping a puddle is not tied to thumb or rpm only) but we (ol' Pro owners) still have one tied to our thumb. It gives oil according to 2 things, thumb (how far you open it) and rpm. No thumb, low rpm = little oil. Lots of thumb, high rpm = lots of oil. Little thumb, mid r's = not enough oil,,, maybe.
You have to picture this in your mind and be aware of it (no matter where your oil pump is set). Ol' time riders blip the throttle while cruising. This cools the piston with fuel but also feeds the puddle that lubes your motor. New pistons or old like that lube. They like it more than the bearings in the crank.

Here's a picture to put in your mind. You unload and idle the sled to temp (I'm not a fan of long long idle times but I wait for the thermostat to open once). If you idle long enough, the sled begins to smoke. You have a puddle in there and things are good.
Now you take off down the trail and you're just cruisin' with 1/8th throttle and 6000 rpm thinking your being easy on the motor because of no thumb and mid rpm. Not!

While your going that mile or 3 of little throttle and mid r's the engine has used up the puddle because little oil was coming in and internal velocity was sucking it up.
Then you give it a romp for a short straight and it takes a bit for the ol pump to catch up. Basically you ran you motor out of oil for a few seconds.
New pistons or rings don't like this very much. If you saw a different colour on your rod tops (even worse rod bottoms) while replacing pistons, I suggest you put this picture in your mind. If you didn't, rock on.
Premix is constant supply of oil to keep the puddle full. Oil injection, the old way, of throttle position and rpm is not. It is variable with the user being an important part.

Not very often do you read about a Poo 800 blowing up while wide open, climbing a hill. Lots of stories about "we just left the trucks" or "just heading back" and it just quit while "cruisin' or "look at my pistons after a few break-in rides".


MO. This is the real reason for "you were lucky and got a good one" or not.

A few heat cycles is mandatory with a forged piston (Wiseco).