During our previous mini-quad run, my son's Pred-90 bogged going up a "normal size" hill. Discovered we had to clean our front brakes from that accident. Darn lucky he didn't get killed!!!!!

One week later, I put the Pred-90 tail up on a car stand and gunned it above 1/2 throttle. I know, this is against my nature but someone once said, its suppose to blow the carbon out of the system. It ran wide open for approx 15 seconds, gave a few small pops, reved back down and its engine died. It would randomly fire but wouldn't completely start.

ok? Check stator output wires - they were good. Check compression and it kept reading 97 to 103 range. Very strange because approx 1.5 months ago, it was a consistant 120 PSI. Ok, maybe its my PSI guage. Its an inexpensive gauge, so I don't always trust it.

Tore its carb apart - expecting mass crud in the bottom of it. It's bowl was clean. At night, I could see a bright yellow consistant flash from its spark plug. That was ok. I checked PSI and it was at 100 (inconsistant). MMMMM.... That ain't right!!!!

OK - Time to "pull the head off". Oh - what a surprise!!!!


For pictures, surf: - Press Here for pictures -


Based on the color of the head and piston, do you know what caused this "melt down"???? Cheap pre-mix oil, improper mixture, improper jetting or water in the gas????


Note: Oil Injection removed and running 32:1. Brand of oil is "off the shelf" Castor.


Thanks.

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All I noticed at first glance is a little carbon build up. Where is the damage?

 

Hard to say from the pic,s. Looks like it got hot and the ring,s lost there tension. My 2 pred 90,s compression went down also to about 100psi, Did a top end rebuild with stock parts and took 50thousand off the top of cylinder. In the end I had 140psi. I would like to know how the big bore kit work,s for you.

 

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You guys are right. I took the piston & head to my local Honda dealer. Just got back 2 seconds ago. He said there's lots of carbon build-up, signs of "average" ring wear but other then that, it should work ok.

My next step is to "super clean" the engine case (where the new case gasket goes) and install the 53mm Cylinder/ Piston upgrade. I'll probably do this tomorrow - since we don't have very good lighting in my gararge. Thanks for your feedback.


Oh, I also picked up some good Pred-Mix oil. A few folks told me that Castor is "average" pre-mix oil. Need the "better stuff" for the new WRH Racing head upgrade. One thing I did notice, the aluminum replacement head is 1/3 the weight of the cast iron factory cylinder. Bet the racers love the light weight of these head replacements....

Thanks for your feedback....

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Did you get your new piston in yet. Hows it work more power. Details!!

Roman

 

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YES - I got the new 53mm piston & aluminum head installed. Finally!!!!! Many thanks to many folks for helping me "bring life" back into our Pred-90. She needed some "mouth to mouth" and Chest Pumping, but she's now alive!!!!

A few moments ago, she fired up and I let her idle for 2 minutes. Then, I shut her down. Without the plastic casing on, I didn't want to over heat it. During this 2 minute period, I did NOT rev it. Didn't even touch the throttle. Need to follow the below "break in" instructions BEFORE we can rev it. But I can tell you one thing, she feels like there's much more power under the hood. Engine PSI is now at 130. Once I re-torque the head bolts down "again" after 15 minutes and 1 hour of engine time, its PSI might even go higher. Only time will tell.....

Long story short.... I can't tell you how much more power at this point in time. But I can tell you, replacing a 2 stroke head is only 4 nuts, 2 gaskets and 1 C-Clip. The fear of doing a head upgrade myself was more painful then doing the work. Man, I still can't believe how easy its head upgrade was.


For break in, surf cut / paste from another forum....

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After engine has been installed and all fluids replenished (coolant/water, gear oil etc) you must then break the engine in properly.

Improper break in results in lower reliability and possible engine seizures.

Use the gas and oil mixture ratio that you intend to run after the break in. Check all fluid levels periodically during the break in. Check the carb jetting periodically during the break in.

Part 1

Idle: Start engine and let idle with a fan blowing on the radiator to help it cool properly. Let idle for 15 minutes.
Cool Down: Shut engine off and let engine cool for a minimum of 30 minutes.
Idle: Repeat first step.
Cool Down: Repeat second step.

Part 2

Note: Be careful not to put unnecessary strain on the motor during the break in. Do not climb large hills or go through deep mud. If possible use a mild treaded tire. If you are on the sand do not use sand paddles.

Ride: Ride for 15 minutes varying your RPM not to exceed 50% of normal riding pace.
Cool Down: Shut engine off and let cool for a minimum of 30 minutes.
Ride: Ride for 15 minutes varying your RPM not to exceed 60% of normal riding pace.
Cool Down: Shut engine off and let cool for a minimum of 30 minutes.
Ride: Ride for 15 minutes varying your RPM not to exceed 70% of normal riding pace.
Cool Down: Shut engine off and let cool for a minimum of 30 minutes.
Ride: Ride for 15 minutes varying your RPM not to exceed 80% of normal riding pace.
Cool Down: Shut engine off and let cool for a minimum of 30 minutes.
Ride: Ride for 15 minutes varying your RPM not to exceed 90% of normal riding pace.
Cool Down: Shut engine off and let cool for a minimum of 30 minutes.
Ride: Ride for 15 minutes varying your RPM not to exceed 100% of normal riding pace.
Cool Down: Shut engine off and let cool for a minimum of 30 minutes.

 

I used to think you had to do all that. Now I hot and cold it a cpl times then do what MacDizzy said" run it like ya stole it". LOL
Besides, on a CVT, it's hard to say what percentage of rpm's it's at if the clutchs are working properly. Testing this Eton I just built, when it hits, it immediatly goes to 11400 rpm's then the clutchs work.
I did see a dull piston.Dull=Dirt they tell me.
I like synthetic oils. [img]i/expressions/face-icon-small-smile.gif[/img]

 

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I get dizzy looking at those recommends as well. Since we'll be "ripping up our yard" in a few more days, I'll ask my son to take it for a few spins around our house. I'll turn the throttle down to 50% and let him have some fun - during 15 minute intervals. If my daugther is up to another ride, she can take it for a spin "around the house" as well. In the end, I'm sure our "around the house" rides for the next week or so will be the same as the recommended break in time intervals. Then, we'll drive it like he stold it!!!!

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defcon5,

She ran 2 minutes with no fan cover on the engine, let cool for 30 minutes. Let idle for 15 minutes, let cool for 30 minutes. Re-torqued the head bolts to 12.5 lbs. Idle for 5 minutes, let cool. Just checked the engine compression with full throttle. With a sore leg, she leveled at 152 lbs. If wondering, the previous 130 lbs was with NO carb on the intake. This test was primarily to check the seating of the rings. Hopefully, my kids will be able to take it for a short spin around our yard tomorrow. If wondering, "the big kid" (that's me) has dibs on 1st drive. One of those "pit crew rules" things....

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jack, lt80

have you run the eton at any national events yet? there was one in the 90 sr. class at budd's creek that was tearing it up.