Are my clam shell gear case half's mismatched? RDE-17 25 hp 1955 Johnson
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- This topic has 7 replies, 7 voices, and was last updated 5 years, 2 months ago by fisherman6.
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January 20, 2019 at 3:12 pm #164094
The gear case on this motor had definitely been worked on. All the paint was removed from it. I just put in a new prop shaft and sealed it with Scotch 847. The lip on the one half is about a 16th of an inch.
I put a match head in the picture for comparison.
How long should I wait for the 847 to dry before I do a pressure test on the gear case?(its pretty cold here)
Are my clam shell gear case half’s mismatched?January 20, 2019 at 7:49 pm #164135My understanding is the the gear cases are a matched set. You can’t mix and match.
January 20, 2019 at 8:05 pm #164137https://aomci.org/forums/topic/mix-lower-unit-gears-and-gearcase-halves/
Here is background from a previous discussion of your question. It does look like yours are mismatched. I think a pressure test is the way to go. If it passed I would run it a bit, maybe a half hour, then check the oil to see if it is contaminated with water, Do not run for long without checking as these gearcases can run for awhile after the oil has leaked out and the casing is filled with water. But that will ruin the bearings and gears. (expensive).
- This reply was modified 5 years, 2 months ago by olcah.
January 20, 2019 at 9:15 pm #164143https://aomci.org/forums/topic/gear-case-pressure-testing/
Above has a great way to check for leaks using air pressure and soap bubbles without test equipment from Mumbles.- This reply was modified 5 years, 2 months ago by olcah.
January 21, 2019 at 12:36 am #164145I did read a thread here maybe a year ago, that said even though they are matched at the factory, our members have successfully used gearcase halves off different motors .
Hope those members come forward and comment on their experience. Can’t remember what year /models were mentioned."Some people want to know how a watch works, others just want to know what time it is"
Robbie RobertsonJanuary 21, 2019 at 6:07 am #164146Sometimes they fit like that. There is nothing in the pictures you have shown that would, alone, make me think they were mismatched. When they made those gear cases, the main parts came from two separate molds. The flats were then machined, it was bolted together and then line bored for the bearings. What makes the complete units a “Matched set” is this line boring, not the castings themselves. Now, if the parts are different colors or something, that’s another story.
Long live American manufacturing!
January 21, 2019 at 10:28 am #164152On the Big Twin/RD split gearcases, the front bearing race and the rear bearing keep everything lined up automatically in the sideways direction but what can be a concern is the machined depth of the cavity for the front tapered bearing, which is also the thrust bearing taking the forward load of the prop.
The prop shaft should be driven forward while tightening the screws, as this will help seat the front bearing squarely in the housing and as long as there is a small amount of end play and the prop shaft turns freely, you should be OK. Doing a dry run first without the pinion or gears installed will let you know if the shaft is free or not.
As stated, the gear housings were made with two separate pieces from two separate molds or dies and then mated and machined together. The housing wasn’t cast in one piece and then cut in half. What you’re looking at is the amount of tolerance OMMC allowed between the two dies. The quality control and machining tolerances must have been quite tight back then as I have done a few of these swaps with no problems although in a perfect world, a complete gear housing swap would be ideal.
January 22, 2019 at 7:36 pm #164327I have done several skeg seals on these split clamshell gearcases without any issues. Knowing they were line bored after assembly as a matched set, I am careful about it and I always dry-fit them before adding sealer and putting them permanently back together. With all the parts installed and everything clean I put the halves together and look for daylight between the halves and check the gap with a very thin feeler gauge or piece of metal shim stock while pushing the halves together. If no gaps are found, I go ahead amd seal it up. So far so good. Keeping the set matched is preferred, but they generally do interchange acceptably in my experience.
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