XR4 Lower unit swap?

[paulrodbender]

1988 150 XR4 - OB264398 - At the moment I have the smaller 1.78 gearcase and I believe my lower unit is having some gear issues. I'm thinking of replacing it with the bigger 4 3/4" case as this is the second time with this problem. A few question I have and appreciate any info, thanks in advance.

What gear ratio should I use (1.87 or 2.0)?
I'm running a 24"P (4 blade) prop now, can I use this prop with the smaller diameter or do I need to go bigger diameter?
If I need a new prop, any ideas on what size, to start at? (3 or 4 blade)

Again, thanks for the help. Engine on a Ranger 374V with a 5" manual plate.

Have a great Independence Day!

Paul

[robinr011]

Hello Paul,
I run and 89 XR4 with a 4 blade trophy on a 18ft Astro with a 5" setback and I get 5700 RPM Med load. A 24 four blade sounds way to high for that application... What is your RPM top end and hole shot

robinr011

[paulrodbender]

Right now, I'm getting 5600 RPM. The setup now is great and she runs well but I do believe the prop may have been worked over by H&H propeller. My problem are my gears in the lower unit are binding and I'm thinking of going to the bigger lower unit. I've had enough of this small one.

[paulrodbender]

XR4 2.jpg

[JOE54]

1;87 ratio , try your 24 first, lets see how it does, boats gonna act completely diff with large gearcase all for the better, done many and they work great

[paulrodbender]

Thanks Joe...... Going shopping for a 1:87...

[paulrodbender]

Just wanted to update, Joe. Replaced lower with a new SEI and now found out my hub is spun on my prop. Out looking for a prop to try and go from there.

[OldTimer57]

I had the successor (XR6) with the 1.78. It came with a 24p prop and ran just fine. If you go to the 1.87 you will probably want a 25p prop instead since it will be spinning a bit slower at the same engine RPM.

[EuropeanAM]

Just wanted to update, Joe. Replaced lower with a new SEI and now found out my hub is spun on my prop. Out looking for a prop to try and go from there.

Hope it works out for you. See a lot of problems with the aftermarket gearcases, break-in is "tedious" at best, and if ever used in a tournament: No warranty.