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Old 04 October 2016, 16:43   #1
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Seized lower unit bolt

Trying to replace the impeller on my new (old) johnson 4hp. One of the two bolts holding the lower unit together refuses to budge. I cant see any way of getting penetrating oil right into the threaded section, any ideas? Thanks
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Old 05 October 2016, 01:23   #2
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Get some heat on it. A small blowtorch works well
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Old 05 October 2016, 01:37   #3
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Tim, problem is the outboard is a long shaft, so the two bolts are a fair bit longer than normal. Not sure heat would get down to the threaded bit. I might book it into a local garage and see if they can rattle it off with an impact wrench or something.

Cheers

Simon
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Old 05 October 2016, 02:49   #4
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I got myself one of these - https://www.machinemart.co.uk/p/clar...impact-wrench/

Its amazing how many times ive used it since having it handy, and with Max torque of 450Nm it gets almost anything off!
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Old 05 October 2016, 02:55   #5
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Thats not a bad shout. As a carpenter I do have an impact driver. Never been sure if its basically the same as an impact wrench, got some hex attachments for it but not sure if its a metric bolt or not.
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Old 05 October 2016, 06:21   #6
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Its likely it'll snap, but you don't want it to snap flush with the thread, so cut /drill the head off and take the lower unit off, then you can get heat and oil to where you need it, onto the thread end and unwind with mole grips
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Old 05 October 2016, 07:13   #7
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Good advice from Samt... my first thought is that's going to snap and be a pig to drill out.

If you took that advice further if you have access to a welder you can weld a nut onto the remaining thread. Often the shock of the weld heat will break the corrosion seal and as you have already lost the tension on the threads in many cases the stud will just wind out with a spanner on the nut.

It's worked for me time and again on old farm equipment.
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Old 05 October 2016, 12:32   #8
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Its not the thread that is seized, its the shank of the bolt. Give the middle 2" of the spacer plate at the front a right heat and it will come out. The bolt above the propshaft is the nightmare. Give it a heat after you take the front bolt out . You may get enough movement to work it slack. There are no dowels on this gearbox so you will get to twist.


In other words get a grinder out and cut through the 2 bolts and buy a used spacer and 2 new bolts on ebay. You really have a nightmare on your hands....
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Old 05 October 2016, 12:53   #9
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Blimey thanks for the advice, I think... going to bribe the mechanic at our yard to take a look first. Yes, the offending bolt is the one at the tail end above the prop...
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