Hello friends,
The subject of crankshaft installation has come up a few times, so I decided to make a quick post about it here. I'd like to encourage everyone to chime in with any added advice or recommendations.
Using physics to your advantage when doing a crank install will make the job much easier. I've made a couple of videos, that many of you have probably seen... they take a few minutes to download, but they do work nonetheless.
http://www.scooterinvasion.net/crankbearings.html
I recently saw the method of using heating and cooling when assembling a lower end referred to as "caveman-style" (or something close to it). Heating the carters and cooling the bearings allows you to very easily drop the bearing into the carter with no force at all. Less stress on the bearings means that they will have longer life and provide better reliability. This is the way that many professionals do their crank installs, and have been doing it this way for years with no troubles.
There's a lot of controversy as to what the best method to heat the carters is. Many people strongly advise against propane, though I personally find it quite suitable and handy, if done correctly. Some alternatives are ovens, heat guns, and 'hot plates'.
The general procedure of installing a crankshaft would be along these lines:
1. Place your crankshaft and bearings in a refrigerator. These parts, when cold, will contract. You can place them in a freezer too, if you want, but I find that freezing them produces much more condensation when you take the bearings/crank out of the cold. Water isn't good on bearings, and the fridge gets them cool enough.
2. Heat one of the the carters with your torch, oven, etc... Usually you should spend about 5 minutes evenly heating the bearing saddle in the carter so that it has a chance to heat and expand throughly.
3. When the bearings are cooled, and the carters are heated, you can remove one of the bearings from the fridge, give it a quick clean up, and ensure that the outer race of the bearing is clean and moisture-free. If the carter is hot enough, you should be able to literally drop the bearing into the carter. It's simple.
4. Repeat the previous two steps for the other carter.
5. Now you should have bearings in both carters. If you're using an oven, you can pop the carter halves in the oven to re-heat the carters with the bearings installed. If you're using propane, you need to find a slug to heat, so that you can transfer the heat from the slug to the bearing. NEVER use a propane torch directly on a bearing! It only takes a second to overheat the metal cage in the bearing and render it useless.
6. I usually prefer to install the crankshaft into the right-side carter (the smaller one). Because of it's size, it'll be easier to assemble with the crank in the this half than the larger one. Remove the crankshaft from the fridge, and drop it into the bearing that's in the smaller carter. Let this sit off to the side while you heat the opposite bearing.
7. I prefer to use Permatex Motoseal 1 (Grey) to seal my engine. It's very similar, if not the same formula used in Hondabond and Yamabond. Be sure to spread your sealant on the machined edges of the small carter where the carters join together. Make sure your locater pins or locater dowels, as they're sometimes called, are in place.
8. Once you've heated the bearing in the large half, you should be able to firmly but easily slide the crankshaft through the second bearings, and close the carters together. Install the screws that hold the engine halves together, and you're ready to re-assemble! Don't forget to install new crankshaft seals before you put everything back together.
This is something that can be frustrating the first time around! Take your time, and be thorough and clean about it, and you should be okay. It does take a little bit of practice to get the timing and everything perfect, but it's really not too tough after you get the hang of it.
Just as a little 'backup' to the caveman comment, here's what Eric Gorr says in his book, "Motocross and Offroad Performance Handbook" on page 127.
Eric Gorr said:
Bearing Removal and Installation
The best way to remove or install bearings is to heat the aluminum crankcases with a propane torch, and then use a hydraulic press out gently push them out. Never pound the bearings out with a hammer and punch. The outer race of the bearing is the only part where a press slug should be placed. Large sockets or discs work well as press slugs. Placing the new bearings in the freezer for two hours and heating the cases with the torch will enable you to install the bearings without a press. Fit the bearings into position with as little stress as possible exerted on the crank ends. Some manufactures (Kawasaki) make special tools that wedge in between the flyweights so you can press the crank into place. Other manufacturers use a threaded tool that draws the crank into the bearing.
Eric Gorr said:
Crankshaft Installation
Here is a simple way to install the crank. Place the crank in a freezer for two hours so it contracts in size. Get a cylindrical piece of aluminum with the same diameter as the inner bearing race. Heat and expand the bearing's inner race by heating the aluminum slug with a propane torch for five minutes while it rests on the inner race of the right side main bearing. Drop the cold crank into the hot right main bearing. Repeat the procedure for the left main bearing. Drop the cold crank into the hot right main bearing. Repeat the procedure for the left main bearing and prepare to assemble the cases.
I hope that with this post I've clarified some of the confusion about crankshaft installations. There are some variations that other people take, but in general, the principal remains the same. Using heat to expand and cold to contract the parts so that you can assemble them with no force is the basis behind the whole thing.
~Josh