"Easy" Powerhead Swap 4hp 4W75A into 4R76M not so easy!

cprodave

Petty Officer 1st Class
Joined
Jul 1, 2012
Messages
301
I am trying to remove the Powerhead from Exhaust Assembly on a 4W75A (which runs great has Transom Clamp broken, badly eroded paint etc.on lower unit) to install on a near-pristine (except blown cylinder/crankcase!) 4R76M. Crankshaft and all other necessary mating parts are identical between the 2 engines (Flywheels and other non-mating parts are different--I know). I have completely disassembled the recipient 4R76M so I am quite familiar with how it is configured. But I am stuck on what should be an easy step! I removed the 6 bolts which hold the 4W75A Powerhead to the Lower Cover 0388044 and Exhaust Housing 0314813. On the 4W75A I can raise the Powerhead/LowerCover about 1/8inch from the Exhaust Housing 0314813 but get a lot of resistance lifting further. The Gasket 0315338 has separated cleanly from the Exhaust Housing, i.e. stayed with the Lower Cover. So I don't have a gasket (with gasket compound etc) holding things together. Could the copper cooling pipe be stuck in the rubber bushing in the bottom of lower unit near impeller? Could I cause any damage by "brute forcing" the Powehead/LowerCover apart from the Exhaust Housing? Any help would be appreciated...
 

kbait

Commander
Joined
Nov 13, 2007
Messages
2,446
Remove lower unit before going further. Drive shaft should stay with gearcase upon removal. If driveshaft splines are stuck in powerhead, impeller key will prevent powerhead removal (and lower unit removal). If stuck, you can try pb blaster dribbled onto driveshaft splines, pry harder, etc. post back w/findings.
 

cprodave

Petty Officer 1st Class
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Jul 1, 2012
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301
Lower unit has not yet been removed. I will look at that scenario (Drive Shaft stuck in Powerhead) tomorrow. Thanks!
 

cprodave

Petty Officer 1st Class
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Jul 1, 2012
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Sorry for delay in advising. The 4 bolts attaching 4W75A Lower Unit to Exhaust Housing seemed seized, so I soaked them with Marvel MysteryOil and WD40 for a couple days, then removed them. The 4W75A showed milky oil in the Lower Unit. The 4R76M lower unit oil is clear/clean. Another reason to use the 4R76M Lower Unit and part-out the 4W75A. Both Lower Units are now loosened/reattached. I will next use PBBlaster/MarvelMystery,etc to get the Powerhead removed from the DriveShaft on the 4W75A (both engines have a 318482 Driveshaft--I checked that compatibility long ago).

If I remember correctly, the best way to remove Powerhead from Driveshaft is to "bearhug" the flywheel with one arm (to lift the engine) while hitting the TopNut (previously loosened a couple turns from Driveshaft) with a heavy mallet or hammer (being careful to not damage the threads on the DriveShaft), right? Better yet, get a 2nd person to lift the flywheel/engine???
 

cprodave

Petty Officer 1st Class
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Jul 1, 2012
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301
Oops, I remember now the above BearHug removes the flywheel from the crankshaft. what's a good trick for removing/prying CrankShaft from DriveShaft (after soaking)?
 

cprodave

Petty Officer 1st Class
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Jul 1, 2012
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Hanging engine upside down with generous padding underneath. See photo. Should I be concerned about breaking the impeller key? I have sprayed the DriveShaft/, Crankshaft area best as I can reach with WD40 (fresh out of PB Blaster). Has anyone ever been completely unable to remove Powerhead from DriveShaft?
 

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cprodave

Petty Officer 1st Class
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Jul 1, 2012
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301
Well I gave up at least for now on removing the Powerhead. After drizzling Liquid Wrench into the Crankshaft/DriveShaft area even with 2 crowbars I got not separate. Reading other threads, I see this impasse happens quite often. I see no reason to cut the DriveShaft, drill out the stub, etc. So I am going to fix the lower unit on the 4W75A (needs Transom Clamps unseized, possibly a Lower Unit Seals replacement and a new prop. I might part-out the 4R76M lower unit. Anybody interested in buying?
 
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