S3 Race Custom Modified EC250 Complete Rebuild

[GMP]

Normally, no where near what you heated the cases to for the install. Nothing wrong with the polyamide cage, the NJ series open two piece roller uses one as well. It's the logic in choosing a sealed part that is flawed IMO.

While your in research mode, what material used for the seals? What is its compatibility with fuel components, especially ethanol?


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[Jakobi]

Originally Posted by GMP

Normally, no where near what you heated the cases to for the install. Nothing wrong with the polyamide cage, the NJ series open two piece roller uses one as well. It's the logic in choosing a sealed part that is flawed IMO.

While your in research mode, what material used for the seals? What is its compatibility with fuel components, especially ethanol?


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So you think I'm good to go Glenn? I appreciate that you pulled me up on the finer details. As always you're on the money and saving me from headaches further down the road.

Heat the cases and drop the mains back in the same was as stock. No seals. I'll have to reseat one of the small bearings on the back side which half dropped out when I heated the cases last night removing the mains. I think I'll slide them both in the oven again on Monday and slip them in between servicing the car.

In regards to the seals:

RSL and RSH seals share many important properties including the elastomer material and reinforcement.
Seals
The RSL and RSH seals are made of acrylo-nitrile-butadiene rubber (NBR), which has an operating temperature range of -40 to +100C and up to +120 for brief periods.
The seals provide good resistance to
- most mineral oil based lubricants
- fuels, including petrol, diesel and light
heating oils
- oils and greases based on animal and
vegetable fat
- water.

From my researching of chemical resistance tables, it seems that Ethanol (Ethyl Alcohol) has little to no action on this compound.

[GMP]

I found "Fair to Good" for alcohols, and "Poor" for Esters, which are a base stock component for some high end two stroke oils like Motul and Redline. Bad decsion, period.


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[Jakobi]

Originally Posted by GMP

I found "Fair to Good" for alcohols, and "Poor" for Esters, which are a base stock component for some high end two stroke oils like Motul and Redline. Bad decsion, period.

Interestingly, I also read that the use of such EP Additives also have a negative impact on the life of polyamide bearing cages. Most noticable when combined with high temps. The wear would still be acceptable for our purposes though. We're talking when aiming for 1000's of hours of use.

[Neil E.]

Nitrile is good for general fluids, but questionable when chemical additives are present. Viton is a much better choice. I prefer metal cages over plastic for this application.

[Jakobi]

Amazing how much simpler things go when you know what you're doing. Basically a 2 minute job this time around. Heated cases sufficiently. Bearings dropped right in. Made sure all were seated properly and left to cool.







Now off to service the car. If I get time later I might start dropping the transmission back into the case.

In regards to fitting the crank, whats the best method? Is it worth while heating the inner race of the bearing using a socket and torch? Or just a frozen crank should drop right in?

[StuJohnson]

This write up and photos is GREAT!!
I have learned a lot.

I am sure you have already seen this, but for others that have not, here you go.
Steps & Photos to rebuild 2-Stroke
http://www.dirtrider.com/features/two-stroke-rebuild/

[GMP]

Frozen crank should do it. Actually sometimes it's just a tight slip fit, and a few taps with a plastic hammer does it. Like I said before it should be nothing like the case fits. Build everything into the primary side case, then seat the ignition side.


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[gearb0x]

just for the folks playing at home would it be possible for you to outline the best methods you ended up with for 1. getting bearings out of the case and 2. getting them back in?

[Jakobi]

Originally Posted by StuJohnson

This write up and photos is GREAT!!
I have learned a lot.

I am sure you have already seen this, but for others that have not, here you go.
Steps & Photos to rebuild 2-Stroke
http://www.dirtrider.com/features/two-stroke-rebuild/

I had looked at that which was great to actually see whats in there and the overall process. I have found using the parts fiche (exploded diagrams) in conjunction with the actual gas gas shop manual has been the most beneficial.

Originally Posted by GMP

Frozen crank should do it. Actually sometimes it's just a tight slip fit, and a few taps with a plastic hammer does it. Like I said before it should be nothing like the case fits. Build everything into the primary side case, then seat the ignition side.

Thanks Glenn. Hopefully it just slides right on in. I've already assembled the transmission back into the primary side case today. Nothing more going to happen until Wednesday.

Originally Posted by gearb0x

just for the folks playing at home would it be possible for you to outline the best methods you ended up with for 1. getting bearings out of the case and 2. getting them back in?

The shop manual advises heating to 150C on a plate or oven. I personally found that heating the entire case halves in the oven at 120C did the trick. My best results where by putting them in and then turning the oven on. The whole case comes up to temp and when the preheat light went out I gave it another 5-10mins to be sure. Using this method most of the bearings would fall in/out of the case under their own weight (or with a tap of the case against a ragged workbench). The exception were the 2 x needle rollers for the gearbox desmodromic. Pri side you can access the other race and carefully punch it out working around the race. The other is a blind fit and I required the use of a blind bearing puller to extract it.

Installation was the same. Needle rollers needed help. I used a socket on the other race and careful worked it in (still on a hot case). The rest dropped right in as long as I took care to align it properly. Pushing it in by hand with a motorcycle glove was enough to seat them all fully.