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Stuck Backplate OS 120 Surpass II Pumped

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Stuck Backplate OS 120 Surpass II Pumped

Old 04-29-2015, 06:49 AM
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tstiffler
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Default Stuck Backplate OS 120 Surpass II Pumped

I have to replace the pump and back plate on my OS 120 but the back plate will not come loose even with heat from a torch applied to the crankcase. Any suggestions? Is there a special tool or something that will pull it out? Thanks for any suggestions.
Old 04-30-2015, 11:13 AM
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bikerbc
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I wonder if it was stuck in there with gasket glue . If so it could be next to impossible. You could stick it in the oven after removing the carb etc .and that way you will be able to heat it evenly ..Then if you had something that you could use to rapidly cool just the back plate . That way it might shrink just a shadow , just enough to crack it loose ? Its just a thought. I am grasping at straws here . Once you have it real hot see if a razor blade could slip into the crack. Can you tell if there is gasket glue in there or just a paper gasket .
Old 04-30-2015, 02:03 PM
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extra300crazy
 
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The rocker arm covers on my 3 O.S. 4-stroke alpha engines seem to be locked on with a type of gasket cement, possibly to prevent oil leakage.
Karl
Old 05-01-2015, 04:53 PM
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A torch isn't the best tool to use, you can warp things with uneven heat. I use a covering heat gun and you just want to heat the case and avoid heating the back plate as much as you can. That plate is a very tight fit and needs to be rotated off with a back and forth motion while pulling up on it. I had one old engine I had to use heat and channel locks on it. The channel locks will mark the case though if it isn't protected. I have a nice piece of leather I put between the parts to keep that from happening.
You can also go into OS support and ask Bill Baxter how they do it. Bax and his crew probably do it every day and have a better way?
Old 05-01-2015, 05:09 PM
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Square Nozzle
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I'm not familiar what your backplate looks like. Any that I have seen are squarish with lobes at the screw holes. What I have done in the past is take a large adjustable wrench and span the backplate lobes with the wrench laid parallel to the rear face of the crankcase but not on the crankcase. That will give you some leverage to twist the backplate.
Old 05-02-2015, 02:10 AM
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tstiffler
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Thanks guys. I've tried the channel locks using vinyl hose over the jaws to protect the finish and I've tried the large straight jawed spanner wrench but that little puppy wont budge with plenty of elbow grease applied. I'll try using a medium sized Stillson wrench next then maybe I'll give OS Service at Hobbico a call and see how they do it.

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