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]

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]

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]

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.

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.

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.

 

[(F5)]

I've done some research and I'm going to use the bearings I have without the seals. As stated above, neither of these bearings have been pressed in or out. The just dropped in with heated cases, and came out with heat and smacking the case against some rags. The fit when back to temp was good and no chance of pulling them out.

The flywheel side bearing is an SKF Explorer series with Polyamide 6,6 cage.

From SKFs website: Solid polymer cages are characterized by a favourable combination of strength and elasticity. The good sliding properties of the polymer on lubricated steel surfaces and the smoothness of the cage surfaces in contact with the rolling elements produce just little friction so that heat generation and wear in the bearing are at a minimum. The low density of the material means that the inertia of the cage is small. The excellent running properties of polymer cages under lubricant starvation conditions permit continued operation of the bearing for some time without risk of seizure and secondary damage.
http://www.skf.com/group/products/b...or-rolling-bearings/cage-materials/index.html
http://www.skf.com/binary/12-36038/6270-EN.pdf

From that it sounds like it will be up to the job. Back on target after dealing with a mega mind bong.

I use those plastic cage bearings all the time & they are great for high speed engines, I try for C4s but C3 if I can't. Bigger engines I'm not so experienced in.

Seals on the mains? yer shiddin me! Only ever seen that once before & it was on an old TS125 engine I bought & was told had been re-cond by a dealership which was a blatent lie & found all sorts of sins including no crank seals (maybe they thought the bearing seals were enough) & internal type circlips instead of plain wire ones (must have been easy to fit, silly factories for not using them, bleeugh!)

 

[Jakobi]

I use those plastic cage bearings all the time & they are great for high speed engines, I try for C4s but C3 if I can't. Bigger engines I'm not so experienced in.

Seals on the mains? yer shiddin me! Only ever seen that once before & it was on an old TS125 engine I bought & was told had been re-cond by a dealership which was a blatent lie & found all sorts of sins including no crank seals (maybe they thought the bearing seals were enough) & internal type circlips instead of plain wire ones (must have been easy to fit, silly factories for not using them, bleeugh!)

Good stuff F5. The flywheel side one is a C4 Peace of mind. In regards to sealed mains. It looks like every GG out of the factory from 2009 onwards has been using them.

 

[Jakobi]

Today I was pretty busy with other things and the bike wasn't a priority, but I managed to set a bit of time aside to get my head around the gearbox. All slid back together as it should and I can put it through the gears. These photos are of it sitting in neutral.

 

[GMP]

The reason C4 clearance bearings are used is to allow a tighter press fit, or to allow a wider tolerance for the press fit than may end up tighter. Jake, from what you describe about assembly your cases seem normal. C3s would be fine in this case. If R&R was tough I'd say C4. Not all bearings are readily available in C4.

GasGas has had problems in the past with press fits. Many '99s were too tight and crank bearings failed often. '00 had a pretty tight case fit, but a very loose crank fit that caused the crank to spin and the journals to wear. I had a '00 250 and '01 125 like this. They then went to the two part roller bearing(a LOT more running clearance than any 6206 radial ball) and all seemed well as a rule. Now we get this mess. I like getting paid for R&D, not paying for it.

 

[Jakobi]

More of your knowledge being shared around. Very appreciated Glenn

Another quick question. The crank shaft o-ring. Where does this go? I know it sits in with the seal and bushing, but it doesn't seem like there is a groove or anywhere to specifically locate it.

Also, when is the prefered time to install all the seals? Before the cases are back together and crank installed? or slide them over and seat them after?

 

[GMP]

Jake,

The oring goes on the crank behind the sleeve. It functions to seal the crank/sleeve just like the design of the countershaft.

Seals can go in first. Its VERY IMPORTANT to only seat them flush, too deep and they can block the oil holes. There are no stops counterbored in the cases. The primary side seal rides on the sleeve, and that(with oring) will be installed with all the primary hardware. Just grease them up good and make sure everything is clean and free of knicks, etc. from all the handling.

If a crank fit is tight in a main bearing, I may leave the seals out and warm the case/bearing for an easier install. I did a motor like this once but I suspect you will have no problems.

 

[Jakobi]

Thanks again. I think I'll hold off and put the seals in at the end just incase if I have any struggles along the way. Already have the trans in the primary side anyway. Taking special note only to install seals flush.

 

[GMP]

Jake,

You can get dry ice down there can't you? Freeze the crank and it will just drop in a warm bearing.


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[Jakobi]

Jake,
You can get dry ice down there can't you? Freeze the crank and it will just drop in a warm bearing.

Should be able to get it from a party supply store.

 

[ollie]

The crank shaft o-ring. Where does this go? I know it sits in with the seal and bushing, but it doesn't seem like there is a groove or anywhere to specifically locate it.

Dont forget the Photo's Jake

Loving this thread

Ollie