Bottom end rebuild

[Jakobi]

Just feeling out the cost of bottom end rebuilds. On average how much does everyone spend and what are they replacing for that price?

I think I'm going to go with genuine Gas Gas bearing kit and seal kit, just for simplicity as it has all the bearings and seals I need. I ordered all genuine gaskets and went with a Vesrah conrod kit. Additionally I'll replace the starter rachet, pinion, and spring, and also the countershaft seals. The kits include kick starter, water pump, shifter seal, and both crank seals. Bearing includes all the gearbox, water pump bearings etc.

I'll fill in parts numbers later.

[Jakobi]

Also, silly question, but will I need a special tool to pull the crank into the cases after its been rebuilt or can I work around it somehow?

[Neil E.]

Usual method is to use temperature to do the job.

Initial bearing install. Warm each case, cold bearing slips in.

Side 1, bearing in case, case warmed up, cold crank slips through bearing. Let cool it cool down completely.

Side 2, bearing in case, warm case up then move quickly to assemble. Warm bearing slips over cold crank.

Doesn't assemble well? Stop, warm up complete engine, pull apart.
Repeat assembly with a greater temperature differential. Still problems?
Measure crank to bearing fits. Maybe polish crank for a better fit.

[Caravan Monster]

I wouldn't order parts until the engine is split and the parts can be inspected. It isn't normally necessary to replace many (if any) gearbox bearings, although I would be inclined to replace the crank main bearings, little end bearing, gudgeon pin (cheaper as part of a piston kit) and all oil seals regardless for peace of mind.

Use of a good quality knife-edged puller to remove the inner race of the flywheel side main roller bearing is helpful. Like Neil E says, hot bearings / cases over cold crank and work quickly to install.

[GMP]

I always do this too, but note this is the easy part. The fit of the crank, counter, and main shafts in their bearing inner races is a lot looser than the fit of the bearings in the cases. I've done a few GGs and these can be quite tight. Removal is not a big deal, you can use a crude driver and a hammer to tap them out with warm cases. Install is different, you NEVER apply force across the races of a bearing. Get dry ice and freeze all your bearings, warm your cases. If by some slim chance you can get liquid nitrogen, it makes things effortless, they just drop in the case bores.

You would be better off sourcing better bearings from a supplier at a lower cost. Good opportunity to get rid of those sealed bearings, goofy idea in a two stroke. A test bed for DI no doubt. There are several better choices. I'd balance the crank and put a set of high quality ceramic bearings in. For steel bearings I'd use either the two part roller used for years, or the M306 series heavy duty ball with a machined cage. I did a '00 and got these for the same price as the OEM.

[Jakobi]

Definitely getting the crank built, balanced and trued. I have been feeling out sources for this locally so should be no issue there.

I thought the same thing as you regarding the bearings Glenn, and have always sourced all other bearings from the shops. I was considering the whole kit purely for simplicity in that I can order it and they'll all arrive at my door. The less variables I have to deal with, and less delays with the cases open the better for my first time. Generally would you replace the transmission bearings and such too? or just water pump and mains?

At this point my bike isn't indicating any failures, and the whole rebuild is purely preventitive maintenance. I'm not looking at doing it on the cheap really, and would rather have a fresh engine. While the stock sealed bearing isn't idea in theory, I can't say I've had any issues in practice over 250hrs and the bike has swam twice over that time. I'm guess I've been happy with its reliability, and can get the whole kit at a reasonable price. Also if I get the kit and you don't reccomend changing the tranny bearings I can easily store them for another 250hrs and then go the other way once I'm a little more familiar with what I'm doing.

I will definitely use blind bearing pullers where requires and use the heat/freezing method to drop the bearings in. I should be able to bring the cases up to around 40C simply by leaving them in the sun, and the bearings to -20C in the freezer. They should drop in easy enough and also have a butane torch which can be used.

Anything else? Would you use a sealant on the main case gasket or just a smear of grease to hold it in place?

[GMP]

40 deg C in the sun is nothing, you have to go up to 100 deg C. Manual says 150, but I never went that high. Hot plate, oven, or by me in the winter when I do such work, wood burning or pellet stove. This heat, and a super cooled bearing(dry ice or LN2), is a drop in affair. It has to be straight though when starting it. The sun and your meat freezer are a joke, don't kid yourself.

I generally do all the bearings while its apart, and upgrade quality as discussed. All the press fits on GG motors are tight, be aware. No retention screws like on some of the Jap bikes.

I always used sealer on the gaskets, but as of late the gaskets are the new rubber coated metalized type. I'd be inclined to put these together dry and clean.

Jake,

Study the engine manual, if you need a copy let me know. Its '05 vintage but very little has changed.

[Jakobi]

Advice onboard! I was also thinking oven. Will just have to plan it for a day when the missus is out I'll get some dry ice too.

I have a copy of the 06 workshop manual which I have been reading and will have a printed copy with me during the rebuild.

The center case gasket I have is only cardboard. I enquired about getting a metal/rubber one but none in stock from my source.

[pscook]

Here's my favorite trick- I wash the engine cases in the dishwasher with hot wash and hot dry turned on. When you pull them out they are HOT and clean. Drop in the bearings and press for final clearance. I have a large assortment of bearing press tools so I set everything up in advance. I do use the freezer (24 hour cold soak) as I don't know where to buy dry ice. Haven't had a problem yet, except that dang CR80R. That was TIGHT.

Anyway, a good idea is to set up all of your tools in advance so you maximize your temperature differential window.

[Rick]

Most Airgas places have dry ice....