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Alpha One MR sterndrive gearbox prop shaft endfloat

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budgie14

Regular Contributor
Hi,Im in the middle of overhauling my gbox on my Mercruiser Alpha One.Reason was water in the oil,and excessive slop in the propellor shaft.after pulling apart and all the usual stuff,Im reassembling using all new bearings and seals,original shims back where they came from.In the GLM parts book,I noticed a spacer washer that went on the prop shaft before the reverse gear.I thought that would solve my excessive end float of the propellor shaft..When it arrived I found it was the wrong size to fit snug inside the reverse gear clutch dogs,[where a shim washer should have fitted].so the question is,how do you adjust the endfloat?Ive got the w/shop manual,and theres no mention of this.I have one millimeter endfloat.is that ok?I have also shimmed both the forward and reverse gears to get correct backlash on the driveshaft.Ive had to put a shim between the reverse gear and the bearing it sits in[which helped a bit with the endfloat] to get the backlash down to a reasonable level.[was excessive].Also,is the forward gear bearing preloaded by the thrust of the prop pushing forward?Ive also read your online w/shop manual which I downloaded.My diveshaft is the type thats thrust upward[no preload pins]./Im using home made tools,wish I had the proper gear.Any advice appreciated
 
Follow shimming proceedures in the manual. With a new casing, gears, bearings etc., you'll have to start from scratch with shimming. Just using the same shims as before and assuming it's good enough is a no no. Lateral movement at the prop on a dog clutch is normal, not normal on cone clutch app.
 
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If your just renewing the seals and bearings,like I am,the manual states to put the shims back where you get them from.[as an engineer,thats what I always do]Which Ive done.If I was going to renew the casing and gears,its cheaper to just buy a brand new one,which in NZ is about $2500,complete.Besides,Im not assuming anything,since when rebuilding gearboxes you have to be bang on with your shimming,thats why Im asking..
 
You are right. When rebuilding the original case just put all the shims back where they were. If you replace the case you have to start from scratch. When done, if you do not have end play in the prop shaft, you have a problem.
 
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