jdoug

Does anyone know what size the PTO bearings are on the 3.5 outboard?

BB Modss

What powerhead, old style 12mm crank or new style 13mm crank?

jdoug

I'm pretty sure the PTO shaft is the same on both models. I also found the size - 7mm x 19mm x 6mm. I'm trying to outsource the bearings for my outboard, but what I've come to find out is that you won't really find any decent quality bearings for any cheaper than what they have listed on the Mecoa K&B site. Most that I've found are the same price or higher for the better quality ceramic bearings or stainless steel.

I'm not sure of the crankshaft size on my engine because I didn't have any calipers around when I had it apart. If it's not 13mm then I will get a new 13mm crank. I thought I had all the bearings really cleaned out good and they were smooth out of the engine. But, when I put the engine back together and turn it over, I can feel a slight gritty feel. So, now I'm taking it back apart to see which crankshaft I have and I'm putting in all new bearings.

Dan S

Yes the PTO bearings are the same for both model and you need 2 of them.

if you replace your crank shaft from the 12 to the 13mm you also have to replace the rear bearing.

Dan

topfuel4430

Also, if you switch to a 13mm crank, you will need a 13mm front housing. And of course the bearings as mentioned.

~James

topfuel4430

Also, if you switch to a 13mm crank, you will need a 13mm front housing. And of course the bearings as mentioned.

~James

Dan S

One more thing, check if you have the .765 Piston and sleeve (OD).

Because if you don't have the .765(OD) when switching the crank/rear bearings and Front housing to the 13mm you may need a new crankcase and piston/sleeve, older crankcase used .750(ID) and the newer crankcase is bored to .765 (ID) and .765(OD) P/L.

Dan.

Does that make sense????

topfuel4430

hey... there is an echo in here... Sorry for the double post.

~James

jdoug

I forgot about the front housing. Dang, more parts to buy. I guess I should ask this question - Is there any reason why I should go with a 13mm crankshaft? I will be running the engine stock with possibly a pipe when I get the bug to mod the lower. It's my first outboard and I've never owned a tunnel.


I am checking the sleeve OD tonight to see which one I have. I am hoping it's the .765


Thanks Dan and Topfuel, you guys have been very helpful.

Dan S

The 13mm K&B (3.5cc) is much better liked by all K&B enthusiast than the 12mm, it is stronger, the port on the crank is bigger and you get a little more RPM and HP, couple this to a good carb (red) or if you can get your hands on a modified Geraghty K&B carb and a pipe you will have a strong contender.

same goes with the 7.5cc updated to the 17mm (from 15mm) much stronger and faster.

Dan.

ob nut

My Feedback: (1)

You're just trying to raise that post count Gabe!!!!!!


From what I have heard, the 12mm is sought after by some very fast people. Could be wrong, won't be the first time.

The 12mm crank will have a "L" stamped on it while the 13mm has a "13" stamped.

topfuel4430

Yeah, we have some very fast 12mm motors also. Not much difference between the two in the performance department. The red carb is too big for the 3.5 OB application, even in a modified version. I have both 12mm and 13mm cranks, without any stamping on them, and also if its an early year 12mm it will have 8935 stamped on it. K&B engines and parts are hard to predict, you never know what youre getting.

My self and Geraghty modify the carbs so that the bore is a magic number between the black carb and the gold carb. The bore change, along with a few other modifications to the carb offer the best fuel draw/spray pattern for our little engines. Rod has taught me many things over the years, and has forgotten more than most know, especially about K&B's. If anyone is interested in learning a good bit of info and having an animated phone conversation, give Mr Geraghty (he hates that) a shout.

~James

Dan S

Your right James, sorry I was thinking 7.5 here for a moment.

I had the pleasure to communicate with Mr Geraghty and buy one of his moded K&B carb for my 7.5, what a difference.

Extremely knowledgeable man and a great guy to talk to.

Maybe the 3.5 is too small to have a big difference between the 12 and 13mm or the gap isn't big enough, but you sure can see the difference with the 7.5cc between the 15 and 17mm.

Dan.