Lower unit gear case flange wore off and prop gap

[Okiehunter]

Hello,

I bought what appears to be a an outboard with low hours - 1983 115hp Johnson outboard with a stainless prop. While having it tuned the mechanic called and said I have a 1/4 inch gap between the prop and lower unit. He thinks the previous owner probably let another prop rub material off the gear case and then replaced the ruined prop with a stainless model that when installed now has a large gap. He thinks I will have cavitation problems. He is talking about installing a thiner flat washer in place of the existing thrush washer in an attemp to close the gap. Should that concern me? Can you recommend any solutions such as a cavitation ring and where I might buy one. Or should I have some additional material welded on the lower unit. Thanks in advance for any assistance you can provide.

Robert

[steelespike]

It may very well cause problems. You might have him use a thinner washer but I would run the boat and make the decision for more changes based on the results.You also might try another oem prop just to check the fit.

[Okiehunter]

It may very well cause problems. You might have him use a thinner washer but I would run the boat and make the decision for more changes based on the results.You also might try another oem prop just to check the fit.

Thank you for the reply. So, using a high quality stainless steel flat washer instead of a OEM thrust washer is acceptable?

Robert

[steelespike]

I can't speak specifically to that setup.You wouldn't normally be able to use a thinner washer but seems like a good way to close the gap a little.

[Maclin]

Do you have any pics of this damage on the lower unit? Pics with the prop off then on may help some of this come to life from your's and your mechanic's descriptions.

I would not use anything but the correct thrust washer. And failing any problems found while running then that may be as good as it gets so to speak.

By way of sleuthing out what the gap stems from, first off I think something is not quite right with the prop. The hub in the new prop could be positioned not quite correctly, I think I would try to find another prop to use just for a fitting.

Just seems like a quarter inch of material being ground off in a prior-to-you event would have created quite a lot of drag on the engine not to mention the extra noise, plus someone would have noticed that the prop that supposedly caused this was on kind of tight! or not I suppose.

Some engines have an anode there between the prop and the drive housing attached to the drive housing. I have no particular knowledge on your engine, just throwing that out as a possibility (that room was left for an anode kit or something).

You may also try posting this in the Outboard section for Johnson motors. There may be a difference in years on these and maybe the prop manufacturers dropped models down to one that fits more years or something, so some have a gap.