Mini 2 stroke's

[400ex4ever]

For those out there with a Mini 2 stroke (My son rides a Predator 90).

How often are you supposed to rebuild the top end? I just recent did a comp test on my son's and it was at 52psi. Stock should be around 100psi. I am getting everything cleaned up and should have it back together soon.

[400ex4ever]

here's a couple of pics of the disassembled motor:

http://sandwizardsforum.com/forum/files/img_0672.jpg

This shot you can see from the piston how bad the top end needed to be rebuilt.

http://sandwizardsforum.com/forum/files/img_0670.jpg

[Spike99]

.

On a Pred-90, the compression should be around 120ish. By the looks of your piston, it doesn't look like your engine wasn't getting enough oil. Our '03 Pred-90 has a stock head within Oil Injection removed. Last week, I did a compression test and it was 120. If you are planning to rebuild the top end, you may want to install a better then cylinder. A cylinder block that's ported, has better then factory squash and has compression between 145/150ish.

Hope this helps.

.

[400ex4ever]

Spike or anyone for that matter,

What 2 cycle oil's do you use?

I have been running the Mobil 1 Synthetic 2 cycle oil. Maybe that is part of the problem.

My cylinder is getting honed and the head shaved. I have new gaskets and rings on order. Should get it back together this weekend.

[300exOH]

The Mobile 1 2-stroke oil may not be intended for oil injection. If you keep the oil injection you may want to make sure you are running the right stuff. It would be better to remove the injection and premix it yourself.

[400ex4ever]

Sorry, I should of mentioned this before.

The oil injection has all ready been removed. I premix at 32:1 ratio. Just thought it might be the synthetic oil causing the problem.

[300exOH]

I doubt it would be the oil then. I'm not sure what the mix should be though??

[Spike99]

.

That piston sure looks "burnt black" to me. Could be the oil ratio, could be the brand of oil, or it could be from over heating. Hopefully, your fan is working really good and its cover doesn't let out too much air.

On the front on my '03 Pred-90 cover, I noticed its OI factory rubber hose covers a hole in its plastic case. If you remove this oil line hose, it creates a hole in the front right corner of the cover. Thus, air flows out this hole instead of cooling the engine head right corner much better. Wonder if that's the source of the "looks like over heat" problem???

.

[LT80]

Your piston also looks very dull. Dull means dirt.
I use Mobile1 in my van, never really knew they made a 2 stroke oil.
My oil recommendations::
1) Torco GP-7..This oil has proven itself to me to be the absolute best in lubrication qualitys.
2) Klotz R-50
3) Maxima SuperM
4) Amsoil
I willl never ever run Golden Spectro or VP oils again!

I get pistons in all the time with ring blow by (the black). I consider it as normal wear.Maybe I missed it, but I didn't see how long the motor has been running with that piston in it. :)

Your replacing the rings only??? I don't believe in that.;)

[400ex4ever]

So I should replace the piston at the same time as the ring. I will have to order it tomorrow.

[Arctic Cat Dad]

It all depends on the condition of the piston. And yours looks very dull in color not shiney. With the condition of that piston I would put one in myself. You don't always have to put in a new piston everytime. My son has a 2001 Polini x3 works race bike. Believe it or not it still has the origanal piston in it. And it still looks brand new. Shiney as a new quarter. It all has to do with how you take care of your machine. Dirt is the KILLER to a piston. Never buy a cheap filter,there cheap in price because there cheap. I always clean and reoil the filter every 3 hrs of ride time. Sometimes even more if it's very dusty. Another thing the type of premix oil has to do with it. Always buy a VERY good premix. I only run Maxima Super M.

[400ex4ever]

It turns out to be the oil causing the problem. From what I understand after talking to raptor720 (miniATV's.com (http://www.miniatvs.com) the synthetic oil I does not disapate the heat like the standard 2 cycle oil. Anyone else heard of this?

I am switching to Maxim 729, as per his suggestion and hope to have it running by the weekend so we can take it out to break it in. I will get some pics and post the when the parts arrive.

[LT80]

Well posibly. If Jon said so,I'll gladly think about it as he's earned my respect.
ALTHO,The Torco is a synthetic and I have not seen any problems with it or the other oils I mentioned. A guy brought me a piston that ran a year on Torco and it looked brand new.

You still haven't mentioned how long your machine was running with that piston in it. I consider that aspect to be vital in figuring out the problem (if any).

FYI: It's maxima 927. I personally don't like that oil. But that's just me. If your in the cold, it separates (look at the instructions). Warm weather applications have no worries there.:)

[Livin4Real]

Like LT said, the 927 will seperate at cold temps (40 and lower)
I run K2 in the cold months in Indy.

[400ex4ever]

My son doesn't like to ride in weather colder then 40. But thanks for the good info.

I just got my motor parts today. I will have to post some more pics of the new and improved beast.

[Spike99]

.

Talk about cold weather riding, below is an email extract I sent to one of my buddies last night...


Talk about fun, my son took his Pred-90 out for another spin tonight. Just a short 1.5 hour spin in our back yard. It was only -22 in my region and I'm surprised we stayed out that long. Talk about fun. While following him on my AC 500i, I also took our other 2 kids for a short double ride. Each of our other kids loved it too. Some Fresh air, some laughs and some "fun times" together. When the night was over, my son got off his Pred-90 and said, "don't know what you did but my Pred is a lot lighter". Lighter??? I almost laughed in his face. Perhaps he's getting older the physically stronger!!!!! Then again, it could have been the customized sprockets (for more bottom end spin) that makes his mini feel lighter. RE: Much easier to spin the back end and do fish tails. Instead of laughing, I said ,"yes - all those modifications work great".


Yes, one must use the brand of oil that is "best made" for the weather conditions in your area....

.

[LT80]

It looks like how long that piston was run will be one of lifes mysterys. :D :D

[markvette]

we build race motors and play motors, so far the best oil we have found is the maxima super m, also i will get blasted for this but mix at 44 to 1. on our race etom i mix at 50 to 1 with the maxima and this top end has been raced for a year with no problems and still holds 180 pounds of compression. also after pulling many heads there is a lot less deposits in the head with 44 to 1 than 32 to 1. also i know it cost a little more but higher octane gas will help. if you run regular switch to premium. we run a mix of half and half 118 and 93 premium but that is because of the higher compression . as someone else said a dirty filter will destroy a top end. make sure the filter is clean and everything is sealed up good so no dirt passes the filter.

Mark

[400ex4ever]

Originally posted by markvette
we build race motors and play motors, so far the best oil we have found is the maxima super m, also i will get blasted for this but mix at 44 to 1. on our race etom i mix at 50 to 1 with the maxima and this top end has been raced for a year with no problems and still holds 180 pounds of compression. also after pulling many heads there is a lot less deposits in the head with 44 to 1 than 32 to 1. also i know it cost a little more but higher octane gas will help. if you run regular switch to premium. we run a mix of half and half 118 and 93 premium but that is because of the higher compression . as someone else said a dirty filter will destroy a top end. make sure the filter is clean and everything is sealed up good so no dirt passes the filter.

Mark

At what compression should I start to think about a 50/50 mix?

I only use premium in all our quads. I was thiking about bumping the mix up after all this. I'll try the 44 to 1 mix.

Thanks