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K&B 7.5 OB main bearing seized

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K&B 7.5 OB main bearing seized

Old 10-10-2007, 05:37 PM
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500 lb. koolaid man
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Default K&B 7.5 OB main bearing seized

Yesterday, I came across an offer too great to pass up, a K&B 7.5 OB in OK condition for only $20. The main problem though is the guy I bought it from informed me that the main bearing is shot, that's why the motor is in pieces. This bearing can be replaced with a new one, correct? Anyone know of a website that sells them? Thanks.
Old 10-10-2007, 05:47 PM
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Default RE: K&B 7.5 OB main bearing seized

Here's the main two places I've bought from:

[link=http://www.bocabearings.com/]Boca Bearings[/link]

[link=http://www.mcintoshcentral.com/rc-bearings/catalog/index.php?cPath=80&osCsid=24511e17ddab954209835e0274c86b57]RC-Bearings[/link]

Shop RC-Bearings first, they have the best prices but not all the sizes or varieties.

Boca has all the sizes and types, but the prices are higher.

I recently rebuilt my K&B 3.5 SS with all stainless steel / ceramic hybrid bearings in hopes of better corrosion resistance due to these engines trapping water. Check your rulebook on what bearings are allowed if your racing. APBA won't allow ceramics in their stock classes.
Old 10-10-2007, 06:30 PM
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Default RE: K&B 7.5 OB main bearing seized

Hey you can try Mecoa.com for the bearing . They should have it .
Old 10-10-2007, 07:03 PM
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Default RE: K&B 7.5 OB main bearing seized

When you order bearings, do yourself a favor, buy ALL of them, not just the one that's seized. It would also be a good idea to add a new flex shaft to your order. Another source for K&B parts, and information, is Gary Preusse at G&M Models. No website, but well worth calling at 630-279-2451.
Old 10-10-2007, 09:36 PM
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Default RE: K&B 7.5 OB main bearing seized

I agree with Chuck. It may be more of an outlay in cost, but it is better than finding out more should have been replaced the first time you fire it up. Use the money you saved (which is a good chunk) and put it towards bearings. You got a super deal there.
Old 10-10-2007, 11:07 PM
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Default RE: K&B 7.5 OB main bearing seized

Thanks for the help everyone, I'll get around to working on the motor this weekend.
Old 10-12-2007, 07:24 PM
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Default RE: K&B 7.5 OB main bearing seized

How do I remove the old bearing? Thanks.
Old 10-12-2007, 09:14 PM
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Default RE: K&B 7.5 OB main bearing seized

Throw it in a 300 degree oven. The aluminum will expand enough to release the bearing
Old 10-12-2007, 09:40 PM
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Default RE: K&B 7.5 OB main bearing seized

Hydro is right, works very well and beats using a heat gun and applying too much heat.

Dan.
Old 10-12-2007, 09:51 PM
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Default RE: K&B 7.5 OB main bearing seized

So I put it in the oven at 300 degrees for 5 minutes or so and when I pull it out using oven mitts I flip it over and the bearing should fall out? I only want to do this once so please tell me if what I just said sounds correct or if there's any errors(time, bearing falling out or not, etc.) in what I plan on happening. Thanks.
Old 10-12-2007, 10:09 PM
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Default RE: K&B 7.5 OB main bearing seized

15mins,

bearing should fall pretty much right out.

Dan.
Old 10-12-2007, 11:31 PM
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Default RE: K&B 7.5 OB main bearing seized

i usually make sure my old wood cutting board is right there by the oven to slap the housings on, and use a good thick pot holder to grip the housing. The more solid the cutting board surface the better too.

It's wise to also get set up before hand while the part is cool with an assortment of dowels or such that you can use to poke or press with if it hangs up. Don't use anything metal that will scar up the castings. The trick is not to get it in a bind or cocked while its on the way out. If it does its best just to straighten it again by pressing it back in and start over with the heat.

Its ok to tap or press on the old bearings, but when the new ones come in you won't be able to do that. Everything should be cleaned and heated well enough for them to drop in or with very little finger pressure. No metal tools. Take note how hot and how long you had to heat the case to get the old one out and try and copy that when the new ones are ready to go in, and chill the new bearings in a ziploc in the freezer a half hour or so before you turn the oven on. If you don't use a ziploc they will frost over thick when you pull them out of the freezer, and the thickness of the frost will crank the heat out of the castings before you can even start the bearing.
Old 10-13-2007, 06:05 PM
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Default RE: K&B 7.5 OB main bearing seized

The above works for getting a bearing out of the aluminum case.. Takeing the bearings off the PTO shaft or crank can be a pain. Use a small bearing spliter and if need be, a bearing puller. Heat won't have any effect on the steel PTO or crank.

I've started to heat up the case using a small propane torch. Hold the mounting lug with vise grips, heat the case up around where the bearing sits. About 30 secs will do, the bearing will drop out. Tap lightly if need be on a hard surface.
Old 10-13-2007, 06:29 PM
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Default RE: K&B 7.5 OB main bearing seized

Thanks for the help everyone. I popped it in the oven for 15 min. and banged it on a piece of wood right after it came out, it still wouldn't come out. I don't have a torch, but I have a heat gun that got a piston and liner out of an old engine. So would a heat gun be safe to try? If so I'll give it a shot tonight. Thanks.
Old 10-13-2007, 07:09 PM
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Default RE: K&B 7.5 OB main bearing seized

I had a stubborn set of bearings that didn't come out until I cranked the heat up to 350. Go a bit hotter and see if that helps.
Old 10-13-2007, 08:13 PM
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Default RE: K&B 7.5 OB main bearing seized

Wow.[X(] 350 degrees, 20 minutes, no good. Again I tried banging it against a piece of wood shortly after removing it.

Next up: hammering while it's in a vice.
Old 10-13-2007, 08:18 PM
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Default RE: K&B 7.5 OB main bearing seized

What bearing are you trying to remove? It is one one on the PTO or crankshaft? Neither of these will come off with heat. The top case bearing and one left in the PTO after the shaft removal will use heat.. Just trying to understand which bearing you are trying to remove.. Sounds odd that 20 mins @ 350 won't let the bearing slip out..
Old 10-13-2007, 08:39 PM
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Default RE: K&B 7.5 OB main bearing seized

normally on a regularly maintained engine removing the bearings is an easy step, but looking at those pics again the bearing steel case could be rusted solid to the case.

It may need quite a bit of effort, maybe letting the crank case soak in wd40 or any other good product to try to break that rust and try the heat again.

Dan.
Old 10-13-2007, 09:16 PM
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Default RE: K&B 7.5 OB main bearing seized

It's the bearing in the picture posted, also showing that heat just isn't doing the trick I'll try soaking it in PB-blaster over night then hammering it out tomorrow while it's in a vice.

Oh yeah, question, I've been trying to get the bearing out by hitting dead center on the bearings side(dead center of bearing, where the inside piece that hugs the bearing sticks up). I'm hitting that hoping it will go through allowing me to remove the bearing, is that the rite way to get it out I hope? Thanks.
Old 10-13-2007, 09:21 PM
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Default RE: K&B 7.5 OB main bearing seized

Ok, working the PTO.. Open up a vise to allow the PTO shaft flat edge to freely spin. The PTO should sit on the vise edges. Then take a punch and hammer out the PTO shaft. Then you can take the PTO and put it back in the oven to remove the bearing(s). Most likely one will be left in the PTO while the other stays on the PTO shaft...
Old 10-13-2007, 10:59 PM
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Default RE: K&B 7.5 OB main bearing seized

Hey , I had an aggravating one like that . I bought all new parts and chunked it . Be careful heating it and then beating on it . The aluminum will warp and will break after awhile . I wish I could tell you something that would make it easier but you have a stubborn one that sounds like it doesn't want to give . Good luck !!
Old 10-13-2007, 11:07 PM
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Default RE: K&B 7.5 OB main bearing seized

I was going to suggest buying the whole PTO assembly to save you the hassle.
Old 10-13-2007, 11:13 PM
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Default RE: K&B 7.5 OB main bearing seized

Might be too late now but an slow cooker anti-freeze bath usually softens the cake that forms between the bearing race and the casting. I've been able to pop bearings straight out taking them out of the crock pot.
Old 10-13-2007, 11:26 PM
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Default RE: K&B 7.5 OB main bearing seized

Thanks for all the suggestions guys. If I don't get it out by the end of tomorrow I'll just buy a whole PTO assembly(not a preference, but glad to be an option).
Old 10-14-2007, 09:25 AM
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Default RE: K&B 7.5 OB main bearing seized

What is difficult about the PTO is that there really isnt a good place to strike the assembly. The bearings are flush against the walls of the housing, and just a small lip going around it to try and tap to the board. You are always trying to strike right at the corner of the bearing, and it doesnt have room to fall out.

I had an idea last night about using a piece of tube or an empty soup can or such to set the housing on. That way the bearing has room to drop if you pick the both of them up at the same time and striking them on the board.

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