Bottom end questions

[Jakobi]

I'm at the point where I have to start getting my head around how to do a bottom end. I've got a few good bits of advice from my local dealer, and dave the engine builder extreme. I think I've got my head around most of the 'how to' and what needs to be done... BUT

What parts do I need? What would you all recommend replacing? All bearings? Do we have a parts list or just get them from the fiche? Press the old ones out and then take them to the bearing shop? If my cranks using a sealed bearing like some have been reported to should I put another in?

Lotsa little questions. I'd like to have everything I need together before I start.

Crank? Do CR250 parts still fit? If so which years? Which brands are recommended as quality? Price is not an issue. Are we replacing the full crank or having someone replace the rod? Crank Balancing? Is it a worth while process? The more info I can get the better.

 

[n_green]

Have cold beer nearby to drink AFTER finishing up. Sorry but that's all the useful advice I have haha

 

[noobi]

CR250 rod 84-01 is what worked previously. No reason to think it wont still work. Vesrah are what I would recommend, but anything Japanese will be good. Or price up one in a GasGas bag if it gets that bad.

It is just the Rod which crosses over, I believe. No reason to do the crank lobes unless they're buggered.
All bearings are seals are worth doing while your in there. Maybe the water pump seal too.

 

[Jakobi]

Even gearbox bearings? Can you use seals from the bearing shop? Any special materials to ask for? Or just buy OEM?

I was considering buying a whole new crank just to simplify things.

I'll be installing an alloy impeller so might as well do the waterpump seal at the same time. I'll add it to the shopping list.

 

[GMP]

Vesrah rod is OEM from GG factory. Crank assy is very expensive, there are a lot of good crank builders at least here in the US. I would take the opportunity to have the crank precision balanced.

I usually do all the bearings, and buy a high grade from a bearing supply. I'd at least do the countershaft and the small waterpump and PV bearings, and get the best. I'd also ditch the sealed crank bearings and go with ceramics or ceramic hybrids that are becoming more common now. M series heavy duty ball or the roller from the '02 - '07 bikes are good too. Never liked the idea of sealed bearings, no need for it.

Be very careful with this job, some of the press fits are quite tight and if you don't have the proper tools and technique you can do a lot of damage. The waterpump and PV governer bearings are a PIA to remove as they are pressed into a blind bore, I ground a set of special jaws for my slap hammer puller to do this. I like to use heat/cold and the least force possible, and NEVER exert force across the race of a bearing if pressing it in. It helps to work with someone who has some experience.

 

[wence]

Definitely send the crank out to be inspected and balanced .I did thids on my 07 made it a lot smoother than it already was.
I got all my bearings from the bearing shop.
You will need a flywheel removing tool(ebay KTM one 1.5mm thread)
Gaskets,o'rings.
All good fun mate and real easy to do so long as you don't rush it .
Cheers Mark

 

[pscook]

Contact Bob Piper at North Tahoe Motorsports. I know that he is in the US, but he can provide a manifest of all that you will need for your rebuild. Shipping may not be too exorbitant, plus he's a fount of knowledge on these bikes. he helped me work through my issues. Full disclosure: this was my first GG rebuild, but I have a lot of experience messing about in Japanese lower cases. Bob helped set me straight and was only an email away from an answer.

 

[Jakobi]

Thanks for all the good advice so far.

I have the flywheel puller. Clutch holder. Case splitter/puller. Will be making up some jiggs to hold the engine in my vice as per Daves recommendation. I'm considering taking the whole engine to my dealers workshop along with my tools and doing the work there so that he can offer advice if I get stuck. Will definitely be using heat to help get the bearings in and out with as little force as required. I have acess to a blind bearing puller (slide hammer) as well.

The rod that came stock in my bike is also a Vesrah. I've been happy with it thus far. I might contact some local shops and see if anyones got any recommendations for balancers. I know one person I trust but he's retired and only really just jobs for mates these days if he's not busy working on his house etc.

Its going to be a bit of a learning curve for sure.

 

[Jakobi]

Whats the best brand to use for the conrod? I've been happy with the Vesrah, but can also source Wiseco, hotrods, prox, and wossner as well as Vesrah. They're all pretty similar price wise. Which one would you choose?

Also, quick question re side to side tolerances. Whats an acceptable measurement? When I pull it down I'll measure everything up and see how it feels before deciding to crack into the bottom. If its still in spec I might see if I can get another top end through it.

 

[Fred1956]

Probably personal choice on rod brand, I've had no negatives with any of the ones you listed.
.8-1.2mm is the listed side clearance range

 

[GMP]

How many hours? My guess is you are well within spec. My '07 is over 200 hrs. and its fine. I've seen local GGs here go 6000mi and are still fine. I only got into the low ends early to correct crank/bearing press fit issues that were not uncommon on the older bikes, but really all else was fine. Only bad mains were on a high hour XC125. Those bikes are still running today.

 

[Jakobi]

It'll be my 4th top end going in and 260hrs total running time that I plan to pull it down. Thats an average of 86hrs per piston. The first one I did at 75hrs. The next at 85hrs. I'm stretching this one to 100hrs based on the last couple being well within spec still. I'm not sure from memory but its heading towards 7000kms now (and over 200hrs) and will likely be aroun 7800kms before it reaches 260hrs.

Thanks for those clearance tolerances Fred.

 

[Jakobi]

Ended up tossing up between ProX and Vesrah. Went with the Vesrah just cause thats whats stock. It was only a few bucks more! The parts pile is growing!

 

[n_green]

Take lots of photos when you do this please. Ill need all the help I can get when it's eventually time to do mine.

So which cylinder will go back on it?

 

[Jakobi]

I'll try my best but usually once my hands are dirty and I'm on a roll the last thing I'm thinking of is taking photos. However, considering I don't know how it all goes together too well myself I'll probably take alot of photos as reference points.

Already have a new 250 slug sitting here so thats what will go back on. It rides better. Less vibes. And the finish on the 250 cyl is worlds better. The head has also been corrected. If/when I bolt the 300 on it'll be having the ports cleaned up and head modded. My hands will be full with the bottom end this time around so less extra work and costs the better!

 

[GMP]

Yeah, I always think it would be nice to do a photo shoot or video of a technical job like a top end or fork service, then realize I need someone else to do the actual photos.

Jake, the GG engine shop manual is pretty decent. Its from '05 but nothing has changed significantly. If you need a copy let me know its no longer in the manuals section.

 

[wence]

Pity you are not here mate.
I could watch and drink while you do the first bottom end.
I had a mate do this when I did my first bottom end.
Just handy to have someone thinking differently overlooking.
Just one word of advice... Always bench check the bikes gear changes and make sure the kickstart spring is exactly as it came out( note the position when removing).
These were two things that got me along the way.
Nothing worse than getting the bike running under the carport after hours of cleaning / rebuilding and then going to put it into gear only to find it won't go
Not a good feeling....
So I've heard???
Cheers Mark

 

[PEB]

I was freaked out before I rebuilt the bottom end the first time. I have since done it three times. This last time on my bike I got to do it twice since the main gasket had a leak. Turns out I got a semi crappy gasket. The contour of it was slightly misaligned to the contour of the cases at the hard bend under where the reed valve sits. Be certain yours is proper by laying it over one half of your case. The newer gasket kit with the metalized gaskets are really nice, that is the one you want.

 

[Jakobi]

All good info.

At what stage can you bench test the tranny? Does everything have to be torqued up? Like basically rebuilt but not back in the bike.

Peb. The center gasket I have doesn't appear to have any metal in it. My RHS engine cover one does though. Do they have different part numbers for the newer ones?

 

[pscook]

All good info.

At what stage can you bench test the tranny? Does everything have to be torqued up? Like basically rebuilt but not back in the bike.

Peb. The center gasket I have doesn't appear to have any metal in it. My RHS engine cover one does though. Do they have different part numbers for the newer ones?

You can test the trans just before dropping on the LH case. It's a pain and doesn't work well as you have to support the shafts and shift drum. Or, just dry fit the LH case with gasket and make sure that the cases seat against each other. NEVER use the bolts to pull the cases together. EVER. If you can not tap the cases together, something is out of place. Last check for dry fit before doing all final install, temporarily install the center case bolts, the ones inside of the stator housing and near the sprocket. Tightening those bolts and spinning the parts will tell you everything you need to know about the case alignment and part interference.