OUTDRIVE HELP

[OCT3162]

HI ALL,<br /> WHILE COMING INTO THE DOCK AT THE END OF LAST YEARS SEASON, ENGINE LOCKED UP AT DOCK WHILE PUTTING ON TRAILER. COULDN'T TURN ENGINE OVER, PULLED TOP PLATE OFF TRANSON & FOUND GEAR ASSY. HAD BROKEN, PULLED COMPLETE UNIT OFF, ENGINE STARTING FINE. SHOP THAT CHECKED UNIT OUT FOR ME FOR REPAIR SHOWED ME THAT BEARING DAMAGE ALSO CAUSED TOP CASE DAMAGE TOO. HE COULD SELL ME A TOP UNIT & REBUILD MY LOWER UNIT FOR 1500.00 (OUCH). I DID FIND A COMPLETE BOAT THAT HAS A CRACKED BLOCK. I PULLED TOP PLATE OFF STERNDRIVE & GEARS/OIL CLEAN, DRAINED A LITTLE OIL FROM LOWER UNIT, CLEAN & NO WATER. CAN PICK IT UP FOR 350. BOTH BOATS 1985 W/MINE BEING 4 CYL. 140 HP MERCURISER, OTHER IS 165 HP--I THINK GM. DEALER SAID UNIT WILL FIT, MIGHT HAVE TO CHANGE PROP DUE TO DIFFERENT RATIO. THEY SAID & IN WRITING, WOULD CHECK THIS UNIT OUT, REPLACE W/P PARTS, RESEAL & HE KEEPS ALL MY OLD PARTS SO HE COULD HAVE MY LOWER UNIT TO MATCH UP WITH THE TOP UNIT HE HAS. MY QUESTION IS WILL THIS ACTUALLY MATCH UP TO MY BOAT? I HATE TO PURCHASE THE OTHER BOAT & FIND OUT IT WILL NOT WORK. SELLDF WILL NOT LET ME TRY IF FIRST. I KNOW MINE IS A ALPHA I. MY TOP PLATE IS SMOOTH, THE ONE I'M LOOKING AT HAS A PERCH ON TOP FOR SUPPORTING WHILE REMOVEING UNIT. ANY HELP??

 

[Laddies]

Re: OUTDRIVE HELP

Yes the unit will fit but it has the wrong gear ratio

 

[OCT3162]

Re: OUTDRIVE HELP

I KNOW MINE IS 1.98R & I BELIEVE THE OTHER IS 1.84 CAN I GET AROUND THIS ISSUE BY JUST CHANGING THE PROP? THANXS FOR YOUR HELP.

 

[Bondo]

Re: OUTDRIVE HELP

1st off,....... Loose the Cap-Lock,...... It's Rude,+ Hard to Read.......<br /><br />2nd,..... The Difference in Ratios equals about 6 or 7 Inches of Prop Pitch,....<br />Depending on Where you start,... You'll Probably Not be able to find a prop with a Small enough Pitch.................

 

[Mischief Managed]

Re: OUTDRIVE HELP

Originally posted by Bondo:<br /> 1st off,....... Loose the Cap-Lock,...... It's Rude,+ Hard to Read.......<br /><br />2nd,..... The Difference in Ratios equals about 6 or 7 Inches of Prop Pitch,....<br />Depending on Where you start,... You'll Probably Not be able to find a prop with a Small enough Pitch.................

Gotta disagree here. The new drive will require a prop with 93% of the pitch of the old prop. If you curently run a 21" prop, you'd need a 19.5" prop on the new drive, to get the same performance.

 

[Haut Medoc]

Re: OUTDRIVE HELP

You will not truly get it right by simply changing the prop........<br />I would invest in a brand new S.E.I. drive that you can pick up on ebay for about $1200. ....JK

 

[Bondo]

Re: OUTDRIVE HELP

MM,.....<br /><br />In the last year,... I posed this question to the boards,+ some of the better Mathamagicians came up the the #s,.....<br />There's aproxamately 6+"s of prop pitch difference between Each step in outdrive ratios........<br />Mercruiser has/does offer 5 Different Ratios for the Alpha series,...1.98s,.. 1.84s,.. 1.65s,.. 1.50s,+ 1.32s......Or there abouts,.....<br />With Your Theory,... That's 7, 1/2"s,.... Actually it's Real Close to 30+"s Difference.......<br /><br />What I know to be Fact is,... <br />A step either Up or Down is Way More than an Inch,+ a Half of Pitch............

 

[Mischief Managed]

Re: OUTDRIVE HELP

Here's the math I used: (1.84/1.98)* 21"= 19.551126" You can substitute any prop pitch in place of 21". I just used 21" as an example.<br /><br />Different math:<br /><br />(1/1.98)* 21"= 10.60606"<br /><br />If you spin a 21" prop with a 1.98: gear ratio, you will travel 10.60606" inches with every engine revolution (assuming no slip). That's what we start with. Then we plug that number into another eqaution:<br /><br />10.60606"/(1/1.84)=19.551126"<br /><br />to find the pitch that will match the same distance traveled for each engine revolution with the new ratio.

 

[OCT3162]

Re: OUTDRIVE HELP

The pitch on my prop now is 21 & the one on the other boat is 19. My friend's boat is 180 hp with exact drive as mine w/21 pitch. Doesn't full throttle rpms play a roll in here somewhere? You all are being helpful.

 

[DHPMARINE]

Re: OUTDRIVE HELP

If prop changes were the answer,there would be no different drive ratios.Just more props.But that would be too easy.<br /><br />DHP

 

[Mischief Managed]

Re: OUTDRIVE HELP

Originally posted by ZIGGIE62:<br /> The pitch on my prop now is 21 & the one on the other boat is 19. My friend's boat is 180 hp with exact drive as mine w/21 pitch. Doesn't full throttle rpms play a roll in here somewhere? You all are being helpful.

Yep, no matter what, you will still need to prop it "right". I was only trying to point out that there is not a huge difference between 1.98 and 1.84 and that it will not take 6" of picth to get it propped right. <br /><br />Would a different ratio be better for optimum performance? Maybe. There should be an efficiency gain by turning a bigger pitch prop at a lower RPM. Would it be worth messing with on a 21 year old boat with a 4 cylinder engine? I doubt it; certainly not if you can repair yours for cheap money by using a drive with a 7% difference in gear ratio and the procurement of a prop with a 7% difference in pitch is so easy. Sounds like you already have all the hardware you'll need.

 

[Bondo]

Re: OUTDRIVE HELP

Mischief Managed,....... I owe You,+ Everybody else here an Apology,...... I'm Sorry.....<br /><br />I guess my CRS is acting up again,.....<br />I had the 7"s nearly right,......<br /><br />I searched,+ found the thread down it D/C,... It's just over a year old,....<br />Andrew Leigh,..BoatBuoy,+ achris supplied the Math,+ there's a few good Theories in there besides,.......<br />Check it out.......... <br /> <br /> This Thread <br /><br />Even though I misspoke,....And,.. By your math a 19" prop will work,....<br />When you figure in the Lesser Torque of the motor,.......<br />I'm Still bettin' Ziggie will be down in the 17" or Less props.........<br /><br /><br />Now,....... If you guys will Excuse Me,.......... I've got a size 11 to remove from My Mouth........ <br /><br /><br />And Btw,........ I Still haven't gotten around to Trying that 1.98/1 with My Torque- Shift Yet,.........<br />Maybe This Season..........

 

[OCT3162]

Re: OUTDRIVE HELP

ALL & MISCHIEF:<br /> Thanxs for all the help & info. This is only the second boat i have owned not counting the waverunner i also have. Wife likes this boat better, now waverunner is for sale. Yes i agree due to age of boat, do i really want to put a lot of money into it. Boat was a deal at the price so i couldn't pass it up. I think i will go ahead & purchase other boat for parts to repair mine, guy i work with will buy the trailer for $100. Thanxs again for help.

 

[Mischief Managed]

Re: OUTDRIVE HELP

Originally posted by Bondo:<br /> Mischief Managed,....... I owe You,+ Everybody else here an Apology,...... I'm Sorry.....<br /><br /><br />Even though I misspoke,....And,.. By your math a 19" prop will work,....<br />When you figure in the Lesser Torque of the motor,.......<br />I'm Still bettin' Ziggie will be down in the 17" or Less props.........<br /><br /><br />

No worries. If it was all perfectly easy, forums would be nothing more than a list of FAQs. It's the interaction that makes it fun and valuable.<br /><br />That said.... I gotta disagree again. If he was propped "right" with 21", he will not need a 17" on the new drive. If he had enough torque to swing the 21" prop, he'll surely have enough torque to swing the 19" prop with the "new" drive. This math is completely linear.