Tohatsu M9.8B - replacing needle bearings

[Kristian S]

I bought a new (to me) used Tohatsu M9.8B aka 'Holy Grail' a couple of month ago but haven't had the time to test it on the water yet. It looks great but I took it to a mechanic just to make sure everything was tip top. Turns out it doesn't sound as great as it looks unfortunately. It has a metallic rattle noise when you rev it and the mechanic told me it was probably a bad bearing in one of the pistons. He said it wouldn't be worth it to have him fix it and advised me to run the outboard with plenty of 2S oil but if the noise got worse I would have to do something about it.

I plan on trying to change the bearings myself and from the few youtube videos I have found it looks fairly complicated but doable. Have any of you tried something similar? I would very much appreciate good advises, links to easy to understand youtube videos, list of necessary tools etc.

[tinker]

Originally Posted by Kristian S

I bought a new (to me) used Tohatsu M9.8B aka 'Holy Grail' a couple of month ago but haven't had the time to test it on the water yet. It looks great but I took it to a mechanic just to make sure everything was tip top. Turns out it doesn't sound as great as it looks unfortunately. It has a metallic rattle noise when you rev it and the mechanic told me it was probably a bad bearing in one of the pistons. He said it wouldn't be worth it to have him fix it and advised me to run the outboard with plenty of 2S oil but if the noise got worse I would have to do something about it.

I plan on trying to change the bearings myself and from the few youtube videos I have found it looks fairly complicated but doable. Have any of you tried something similar? I would very much appreciate good advises, links to easy to understand youtube videos, list of necessary tools etc.

Not a tohatsu but I have just stripped at 15hp 2 stroke mercury that had needle bearings that had failed. I replaced the block for a second hand one. The needle bearings wasn't hard to change, just hold them in with some heavy grease.

Your problem is what damage has if done to the crank journal but you can only look and see/measure before you invest in new needle bearings.

I used Google for a manual and printed exploded diagrams off a parts website. Tbh take loads of.photos as you strip and box all the parts up and. label as they come off.

[tinker]

No guarantee on quality.....

https://www.aliexpress.com/item/1005007059876203.html

[Kristian S]

Thank you for the link. Much cheaper than an original replacement crank assembly but not sure I want to trust AliExpress with something like this.

Was your crank journal damaged from the failed needle bearing and what could damage look like?

I guess it would be a good idea to change all gaskets and other perishables while I'm at it. Are there any other parts that can not be reused after I have taken the outboard apart?

[tinker]

I havent stripped the bad one (removed the crank), I stripped the replacement to clean up and inspect. Both bearings were no good on the old one, one had loads of play and the other was siezed, or very notchy. I can't see how it could have run (it did ) without some damage occurring to the crank. You need to strip your down to see what the issue is. But a gasket set,.carb Rebuild kit and Thermostat is all useful to have .

[User name]

It's a doable job for a confident DIY'er but I don't get why your mechanic wasn't up for it. It's not a hugely complicated job on these engines.

You won't know if it's just the needle bearings themselves, or the gudgeon pins, journals etc until you get stuck in, but generally with needle bearings (unlike shell bearings) the bearing itself takes the brunt of the damage before the conrod/journal, so you may find it's ready to go again with a rebuild kit.

Edit: There's some info on part numbers, diagrams etc over here.

[Kristian S]

I think he meant it would be cheaper to find a new (used) outboard. I'm sure he would do the work if I asked him to.

I am sort of tempted to try out the AliExpress crankshaft assemply if I have to replace the whole thing. The price difference to original parts is quite big but then again the quality difference might be just as big...

[spartacus]

Hi Kristian - PM me your email and I'll send you Tohatsu service PDF manual for 2-cylinder 2-strokes. Has tolerances, etc.

[Kristian S]

Done. Thank you. I haven't been able to find it anywhere.

[Kristian S]

As for tools I plan on getting a torque wrench for the bolts and maybe a big one for the flywheel nut. Are other special tools needed - like a "piston pin tool mentioned in the service manual"? I will be replacing all oil seals as well (there is 1 on the crank shaft and 3 in the head crank case) - do I need seal pullers and installers to do this?

[tinker]

I use a socket to install oil seals, just pick the right size to match the outside wall of the seal and gently tap away. Removing seals normally destroys them tbh.

Have you ordered your parts?

[Kristian S]

Not yet. I want to see what's wrong before I order any parts. The mechanic said it would be fine to use the outboard but if the rattle noise develops I should stop and fix the problem, so I hope I can't wait untill the end of the season before I take it apart.