OMC mismatched upper and lower outdrive ??

[machv1]

Just purchased a 1988 Bayliner with a 3.0L and OMC leg, the original leg was a 2.3L to 3.0L, the lower drive assembly gears are shot because the subsequent previous owner ran a 305 in the boat.<br />My dilema is as follows, the guy I bought the boat from decided to fix it up to resell and purchased a lower drive assembly from a 3.0 - 5.8L and bolted it in , he then bought a 19 pitch prop, and took it on the lake to day, he indicated it was gutless and only reached 32mph and 3500rpm, he is going to deliver me a 17 pitch prop and assured me this would solve the problem. I have paid him in full and will wait for the 17 prop. I have concerns I thought the 19 prop would have performed better. The boat is 19.5 ft . My question is can you mix and match the upper and lower assemblies, what do I need to obtain to confirm my mixmatch will work? Signed sleepless in Canada

 

[WillyBWright]

Re: OMC mismatched upper and lower outdrive ??

Welcome to iboats. <br /><br />The different ratios are mostly achieved in the upper but see the next paragraph. I assume we have no idea which one it is? There would be three ratios, 4-cyl, V-6, and V-8. If you're running a V-8 ratio on a 4-cyl motor, you're gonna need closer to a 13 pitch. But prop pitch can only compensate for so much, the power curve is going to change and there's no compensating for that. If it were only one step different, no big deal. But 2-steps is going to be noticable. You can remove the cap and count gears in the upper. That may be the only way to know for sure.<br /><br />I should also mention that in that year, the lower garcase for the 2.3 was much smaller than the one for a V-8. So that's going to throw some more confusion into the mix. A V-8 would tear that lower apart. I don't know about gear ratio differences between small and large lowers.

 

[Bondo]

Re: OMC mismatched upper and lower outdrive ??

Ditto on what Willy says,........<br /><br />I Wish there was a Polite way to say it,......<br />But,........<br /><br />You're the New Owner of about the Worst Possible combination of Boat,+ Driveline that's Ever been produced.........<br />And this 1 has been Butchered......<br />If there's Any Chance,... At All,..... Give it back to the seller,+ Grab your Money,+ RUN..................

 

[whywhyzed]

Re: OMC mismatched upper and lower outdrive ??

Originally posted by machv1:<br />the guy I bought the boat from decided to fix it up to resell and purchased a lower drive assembly from a 3.0 - 5.8L and bolted it in , he then bought a 19 pitch prop

You lost me there...<br />There is no lower that is for "3.0-5.8"<br />Your drive is a Cobra series.<br /><br />There is a 4 cylinder light duty lower (which some people erroneously refer to as 400 series) and a heavier duty for 6 and 8 cylinder applications (again, people call it 800 series, but it's not).<br /><br />I believe the construction of the upper units is as heavy in the 4 cylinder versions, but the lower is only good to about 150HP. The ratio thing will not likely be solved by prop changes, but maybe...

 

[machv1]

Re: OMC mismatched upper and lower outdrive ??

Well I stopped by the local boat mechanics shop, he looked in one of his manuals and indicated the gear ratio must be the same in the lower unit for both the 400 and 800 series becuase the shim is the same size?????<br />Subsequently, he did note that the needle bearings were different, on the 3.0L and lower there a sealed unit and the 3.0L and up there loose, but will not affect the gear ratio only give you a stronger bottom end. <br />So I still have reservations, this mechanic spent a total of 40 seconds looking in his book, and smelled like booze the entire time we talked. If anyone could shed some light on what kind Heinz 57 outdrive I have it sure would be appreciated, specifically gear ratios. <br />By my calculation, with a 19 pitch only getting 3500 rpm, means changing to a 17 will gain another 350 rpm = 3850, a 15 should get me 4200 rpm, and a 14 pitch should get me approx. 4400 what I should be at. But a 14 seems awfully unusual???

 

[ntheyer]

Re: OMC mismatched upper and lower outdrive ??

Sorry to say, but I don't think this is going to be a quick fix. I think, if you are going to keep the boat, you really need to determine what you are working with. You should remove the outdrive and split the upper and lower units apart and inspect the internals to determine what they are. Only then will anybody really be able to help properly. Otherwise, I think we're all pretty well guessing. I also agree, putting 15 and 14 inch props is band-aiding a problem, and may not even work.<br /><br />Sorry for the bad news.

 

[whywhyzed]

Re: OMC mismatched upper and lower outdrive ??

Originally posted by machv1:<br />he looked in one of his manuals and indicated the gear ratio must be the same in the lower unit for both the 400 and 800 series becuase the shim is the same size?????

By the number of ?????'s at the end of your post... I'd say you're way ahead of us on the advice that's coming....<br /><br />Find another mechanic...<br /><br />You aren't in the Kawarthas per chance.... there's a place up near Catchacoma Lake i'd trust (didn't know coma's were contageous didja??)<br /><br /><br />The "400" (4 cylinder) lower is physically smaller which means the anti-cavitation-ventilation whatever plate may or not sit right in relation to your boat's hull. It also takes a 13 spline prop, as opposed to 15 spline from your old lower<br /><br />Teeth make ratios not shims.