First time Bearing replacement on OS50

[squibcakes]

Hi guys,

My relatively new OS50 hyper has developed a rattle (around 5 gallons of fuee through it). I removed the back plate and can see that the bottom of the conrod has been rubbing on the crank case ever so slightly. It doesn't rub when engine is cold.

Anyway I've decided to swap out the rear bearing but having trouble 'wacking it out'. I've cooked the crank case in the oven for around 10mins at 100C a few times but it's still not coming out.

How hot can I cook the case in the oven and how long without damage to it?:arggg:

Cheers
Squib

[Pinecone]

I would go a bit hotter. 100C is 212F, and most people say go to 250F - 300F. So at least 120C.

Let it cook longer, 15 - 20 minutes to get it hot all the way through.

[DavidH]

Put the engine case in an oven 175 deg celsius for 20 minutes.
Then take the engine out of the oven using a glove so you can hold it.
Slam the back of the engine down onto a piece of wood a couple of times. The bearing should fall out.
Put the new bearing into the crankcase while it is still warm. Use the crankshaft to position the new bearing into its proper place.

David

[Pinecone]

350F? that is a bit higher than I have seen.

[TheBum]

I recently did mine at 220F after unsuccessfully trying 200F. I baked it for about 20 minutes.

I discovered that an old dented aluminum 450 boom worked quite well to knock out the front bearing while the engine was still hot. I just inserted the boom into the back of the crankcase and against the back of the bearing, then hit the boom against the floor while holding the crankcase.

[DavidH]

350F? that is a bit higher than I have seen.

Has worked for me for long tiime. Plus when I am in a hurry, I just take a mapp gas torch and heat the crankcase in the area where the bearing is seated. I am pretty sure it gets hotter than 350 deg. <G>

David

[Pinecone]

Probably. :)

[RC-Bearings]

Heating hotter than 350F risks permanent damage to the crankcase. Temps of above 385F can cause permanent metallurgical changes to cast aluminum and will definately cause temper and heat treat changes to hardened steels.

[VegasBob]

Heating hotter than 350F risks permanent damage to the crankcase. Temps of above 385F can cause permanent metallurgical changes to cast aluminum and will definately cause temper and heat treat changes to hardened steels.


So what temp do you recommend?

[RC-Bearings]

So what temp do you recommend?

Use an oven set no higher than 325F as their controllers have a lot of over- and under-shoot. Leave the crankcase in there at least 10 minutes to allow the temp to stabilize. Most of the time, the bearings will come out easily at around 250-300F.

I do not recommend using torches as there is no way to know how much heat you are applying and the heat differential can cause warping of the case. An air-powered heat-shrink gun is a lot safer as the temperature is closer controlled and it has a lot less heat energy. Even still, you would need to be careful as these things can put out over 600F temps!

[bas de groot]

I just replaced my rear bearing in a OS 91,
"cooked" it for 8 minutes at a temp of 200C
only 1 little tap on a piece of wood and the bearing
comes out verry easily.

Always did it this way and never had a problem.

Regards
Bas

[Pinecone]

I use a heat gun for grip bearings. I keep it moving and use an IR thermometer to check the temp to keep it in the range I want.

[kcasser]

I agree with RC Bearings that you have to be careful with the temps, but in the same breath I'll say that I use a propane torch. My theory is that when you put the crankcase in the oven, it heats the crankcase and the bearings both. They all expand at the same time. By using the torch, I'm heating the outside of the crankcase but the bearings inside stay cooler and drop right out. I tried putting mine in an oven at 100C for a long time and banged it and banged it on a wooden table but it wouldn't come loose. A few seconds with the torch and the bearings dropped right out. Now I know that 100C was not hot enough, but I still like the torch method. When installing the new bearings, however, I put the crankcase in the oven and the bearings in the freezer. They drop right in. Now if I can only figure out if I'm doing the seals/shields correctly I'll feel better. That's in another post.:o

[RC-Bearings]

I agree with RC Bearings that you have to be careful with the temps, but in the same breath I'll say that I use a propane torch. My theory is that when you put the crankcase in the oven, it heats the crankcase and the bearings both. They all expand at the same time. By using the torch, I'm heating the outside of the crankcase but the bearings inside stay cooler and drop right out. I tried putting mine in an oven at 100C for a long time and banged it and banged it on a wooden table but it wouldn't come loose. A few seconds with the torch and the bearings dropped right out. Now I know that 100C was not hot enough, but I still like the torch method. When installing the new bearings, however, I put the crankcase in the oven and the bearings in the freezer. They drop right in. Now if I can only figure out if I'm doing the seals/shields correctly I'll feel better. That's in another post.:o

The COEFFICIENT of expansion between aluminum and steel are different so that the crankcase will expand more than the bearing. You need enough heat to overcome the slight interference fit of the bearing in the crankcase. It is normally 250-300F minimum. Using an oven minimizes the chance of warping the crankcase.