| Author |
Message |
    
Kris F
New member
Username: efemdee
Post Number: 1
Registered: 05-2008
| | Posted on Thursday, May 01, 2008 - 06:47 pm: | 
|
Hey folks, first time posting (sure to be the 1st of many). 
I've got a 1973 Mercury 500 S/N 372xxxx that runs well, but the guy I purchased it from had pulled the lower unit due to a crack.
He also included a 1974 402 S/N 404xxxx motor (powerhead an lower unit separated). Unfortunately, that motor is siezed, and the reverse doesn't work.
I have a line on a lower unit from a 1977 402, S/N 456xxxx.
All three lowers have 11 splines on the driveshaft, 6 splines on the shift shaft.
Casting numbers on the first two lower units are 1643-4930, on the '77 is 1643-6037.
My question is: Will the lower unit from the '77 402 match up to my '73 500 powerhead? I'm not overly concerned about re-propping and gear ratios at the moment, rather just need to ensure that everything will line up before pulling the trigger on a lower unit. |
'Bandit
Advanced Member
Username: timebandit
Post Number: 296
Registered: 09-2007
| | Posted on Thursday, May 01, 2008 - 07:23 pm: |
|
2 cylinder to 4? I dunno. I'll go with no. Maybe. |
Graham Lamb
Senior Member
Username: galamb
Post Number: 3082
Registered: 05-2007
| | Posted on Thursday, May 01, 2008 - 07:24 pm: |
|
Kris, looking at the parts list it appears that the same lower was used on both the 500's and 402's in the serial range you have posted... |
Kris F
New member
Username: efemdee
Post Number: 2
Registered: 05-2008
| | Posted on Thursday, May 01, 2008 - 07:58 pm: |
|
Bandit,
The lower unit from the 1974 40 HP 402 (2 cyl) has the same casting number as the 1973 50 HP 500 (4 cyl). Both are 1643-4930.
The lower on the 1977 402 has a different casting number (1643-6037).
Graham,
Thanks for your quick response, I appreciate it!
Which part list?
I've been trying to decipher this all day, but couldn't come up with a cross-reference.
Can you help me out? I don't doubt your correct (have lurked here enough to know better), but want to be absolutely, positively, certain that I'm not throwing money out the window.
-K |
Graham Lamb
Senior Member
Username: galamb
Post Number: 3085
Registered: 05-2007
| | Posted on Thursday, May 01, 2008 - 08:09 pm: |
|
Sure - go to www.mercruiserparts.com - click on "search with pictures" then "mercury force mariner and other outboards" then pick "mercury" at the top of the list (which is the listing for older models) - then the model and serial range and you will figure out the rest  |
Graham Lamb
Senior Member
Username: galamb
Post Number: 3086
Registered: 05-2007
| | Posted on Thursday, May 01, 2008 - 08:13 pm: |
|
Sorry, missed one link there - after you log into the site the first link to follow is...
"click here for mercruiser, mercury parts blah..."
or just follow this link www.mercruiserparts.com/mercruiser_parts.asp |
Kris F
New member
Username: efemdee
Post Number: 3
Registered: 05-2008
| | Posted on Thursday, May 01, 2008 - 08:19 pm: |
|
Ahhhhhhhhhhhhhhh.
Thanks, Graham!
I'd seen (and downloaded) the .pdf files from any number of other sites, but I didn't recognize or notice the "superceded" category. 
Edit-to-add, Yeah, I figured out the missing link.  |
Graham Lamb
Senior Member
Username: galamb
Post Number: 3087
Registered: 05-2007
| | Posted on Thursday, May 01, 2008 - 08:28 pm: |
|
This site is maintained by "BAM" and excellent Merc dealer in Florida. They have also provided me with really sound advice on how to retrofit post 1995 parts to earlier models (on the small 6/8/9.9/15 models that I generally work on).
Excellent site and a bunch of great guys on the other end of it too |
Kris F
Member
Username: efemdee
Post Number: 4
Registered: 05-2008
| | Posted on Friday, May 23, 2008 - 01:56 pm: |
|
Got the lower unit about 20 minutes ago, seemingly in good condition as listed on ebay. Mercifuly, USPS didn't damage anything during the two-week long trip from Texas to Wisconsin.
With a little fiddling, the unit slid right on, and is currently held on with one of the bolts (the 5/8" nut/stud just in front of the anode hole/behind the exhaust tube).
Couple of quick questions before I run out and plunk the money down on a new impeller kit :
When in neutral, the prop shaft spins freely both clockwise and counter-clockwise with no clicks - I believe this is good.
When the shift lever is in the forward position, the prop shaft turns counter-clockwise with difficulty (turning the motor), and clicks when turning clockwise (with ease) - I believe this is also good.
What has me a little concerned is that whith the shift lever in reverse, the prop shaft will turn both ways with difficulty (turning the motor). Is that normal, or should the box click and shaft turn easily when rotated CCW while in reverse?
Did I do something wrong when installing (gear box controller shaft 340* or so off, maybe), or did I end up with a broken lower unit?
Also, if everything is good with the lower unit, I am wondering about the 3-wire output from the Mercontrol box I have, along with the tachometer type required. Will the output from the box work with a 4/6/10/12 pole OB type tach, or do I need to be looking at something else (invariably more expensive)?
Thanks in advance to any and all who answer!
-Kris |
JB
Advanced Member
Username: beckerjs
Post Number: 999
Registered: 11-2005
| | Posted on Friday, May 23, 2008 - 02:39 pm: |
|
From the merc 35/40 manual, the 402 model was the same except the ignition
fwd= ratchet when turned cw, not ratchet ccw
nuetral= free spin
rev=ratchet when turned ccw, NOT ratchet when turned cw
Thats what it says but it sounds like you have it right. I'll try and check mine tonight.
The control box should have purple for power, black for ground, grey for tach. A normal 2 cycle tach should work. Heres a link
http://ww2.tflx.com/obtachtrad.html |
Kris F
Member
Username: efemdee
Post Number: 5
Registered: 05-2008
| | Posted on Friday, May 23, 2008 - 05:12 pm: |
|
JB, thanks for the heads up on the tach. Knowing that I can use leads of the box along with a "normal" 2-cycle OB helps.
Now, with that said...
By rotating the shift-shaft a bit and reinstalling the lower unit, I can also get:
Fwd: Rotates CW and CCW while turning engine (no clicks)
Neutral: Frespinning
Reverse: Rotates CCW while turning engine, (clicks when rotated CW).
This setup seems to have the engine rotating the right way, and matches both props I have (from the '73 500, and the '74 402).
I'm still a little concerned about not having "clicks" in one gear though...
I still seem to be missing a "ratchet" in one of the gears. Thoughts? |
ikia
Visitor
| | Posted on Saturday, May 24, 2008 - 05:42 am: |
|
That is the way they are ----NORMAL. |
JB
Senior Member
Username: beckerjs
Post Number: 1002
Registered: 11-2005
| | Posted on Saturday, May 24, 2008 - 09:22 am: |
|
as ikia said, normal. I checked mine at home, no ratchet in reverse. |
Kris F
Member
Username: efemdee
Post Number: 6
Registered: 05-2008
| | Posted on Sunday, May 25, 2008 - 07:11 am: |
|
Which way is the prop supposed to be spinning? |
ikia
Visitor
| | Posted on Sunday, May 25, 2008 - 10:12 am: |
|
Well when the motor is in forward gear the prop spins clockwise ( looking to the front of the boat ) Now it will ratchet in that direction due to the design of the clutch dog and gear.It will not spin in the counterclockwise direction because the dogs lock. It has to work this way when the MOTOR is driving the gears!!!---- THIS IS NORMAL---- |
