Tohatsu M40D Build 40 50

[camohunter]

My first rebuild a M40d2. Already done the following:

-Bored .30 over
-wiescos in hand
-Ported and polished
-crank rebuilt and welded
-flywheel lightened
-head cut

I think I'm ready to reassemble. What is the best adhesive to seal the crank case to the block? Any advice will be appreciated since this is my first build.

[Trident]

Here is a document I wrote up for the 4 cyl. Mercs, but this info applies to your question as well. Hope it helps. Copied in below:

Crankcase Sealer… if some is good, more is better, then way too much must be just right.

DON”T DO THAT!

So, you need to seal those machined castings, where there is no paper gasket, on your freshly built or restored pride and joy… what to use?

This info applies to any motor with a two piece block, like the Mercury’s which have half the crankcase cavity cast into the block and the other half of the crankcase cast into a matching cover. Think Mark 55, Merc 500 and the jillion similar models, 2, 3, 4 and 6 cylinders.

I say ‘matching’ because the cover is matched to the block early in the manufacturing process, and a 2 or 3 digit ID number is stamped on both parts, then that assembly is finished machined as one. The really critical operation, here, is the crankshaft linebore and then facing off of the top and bottom end cap surfaces.

I don’t EVER recommend mismatching covers and blocks. It can be done, but not unless you know exactly what to check, have access to a mill and have a whole pile of covers to choose from… don’t go there.

Sealer: Some is good, more is very bad., but its absolutely critical that this joint be well sealed, otherwise you get a nasty drool of leaking fuel and oil, and in extreme cases, a cylinder can even run lean from a crankcase compression leak.

Back in the day, way back, Mercury used white lead as a sealer. Then we went to various goos, some of which worked fairly well, some not so well. I recall needing to tear down perfectly good running race motors for no other reason than to reseal the case cover, as the sealer would slowly dissolve over several seasons. Must have been really good fuel! Never use RTV Silicone sealer here, as gas breaks that stuff down, BTW.

I recommend LocTite 518 sealer. I put a row of small dots of sealer up and down the mating surface. Then I tap, tap, tap with a fingertip to evenly spread the dots into a uniform, very faint coating. If you can tell its red, you have too much… just a faint pattern of pinkish fingerprints is the goal. If any squeezes out as you torque the cover, you used too much.

The danger of too much is a thicker coating will squeeze out at the edges but will leave enough in the gap that the cover is ‘floating’ on a layer of sealer several thousandths thick. (I’ve seen motors, built by others, where this coating was over .010”) This makes the line bore oversize in one direction, no longer round, so now the crankshaft with center main bearing, reed cages, and bearing caps has clearance to rattle around in the line bore. You see that as shiny burnished mating surfaces in badly built motors. What we really want is a perfectly mated metal-to-metal joint with just enough sealer to fill the microscopic imperfection in the mating surfaces to prevent leakage. NO MORE!

The good news is the LocTite sealers, 518, 515, 514, 510, will stay sealed until you mechanically separate the parts. This stuff is an anaerobic resin that cures in the presence of metal and the absence of air. It is fuel proof indefinitely. The different product numbers reflect the hardness and elasticity of the cured product. For our purposes, I’d recommend 518, as the ‘one size fits all’ answer.

Cured LocTite sealer is easily removed with Zip Strip Original formula paint remover, or any similar methylene chloride based paint remover product. Lots of ventilation, then wash. You know
the drill.

[Ron Hill]

Trident, do you do engine work for people? I have some Tiller Handle Racer looks to build some motors for them.

Thanks for your posts they are always very informative. You are a great asset to BRF!

[Trident]

Thank you for the kind words.

Long since retired as a driver, more recently retired from building motors. It was fun while it lasted, but age and infirmity is sneaking up on me!

I still try to post stuff where I think it can help, as these same questions come up over and over as we get new guys working on their stuff.

Jerry

[camohunter]

Thanks Jerry that's some good info. I see u are in WI. Pete Nydahl, from WI, rebuilt the crank on this motor and did the block work.

[Chip Trampe]

If you want to meet one of the great engine builders of all time, come to the BSOA 75th on March 18th. Trident (aka: Jerry Wienandt) hopefully will be there.

[camohunter]

I finally got back on this project. I dropped in the crankshaft and bolted it up last night. Afterwards, I realized I had not checked the Wiesco piston rings to see if they were of different types for the top and. Ottom groove. I did not notice any difference and can not tell any difference when viewing the rings through the exhaust ports.

Does Wiesco use different rings for top and bottom?

Thanks,
Justin

[camohunter]

61726

[camohunter]

61970

Painted last night

[Roflhat]

Looks really sharp in blue!

[camohunter]

61975

Installed some socket caps on the exhaust cover

[camohunter]

6197861980

Here's one of my yamaha 60 carbs with the chokes removed. They are a good bit larger in diameter than the stock 40 intake. I wanted to use 70 yamaha round bowls, but couldn't find any at a decent price.

I've got to open up the intake to match the carbs. Waiting on a gasket so I can scribe a line.

Does anyone know what the size difference is between the yamaha 60's and 70s?

[Roflhat]

I think they're the same diameter, just different jetting. The jets in the 60 carbs might even suit you better

[camohunter]

I think they're the same diameter, just different jetting. The jets in the 60 carbs might even suit you better

I think you are right. From my research I found that the Yamaha 60 and 70 intake manifold and gasket is the same part number. That would seem to indicate that the carburetor throats are the same diameter. 70 carbs come with 145 mains. 60 carbs come with 140 main jets

[Xpress2830]

Hi mr Jerry. Bobby here from Louisiana. Looking for some educated advice for a 95 OMC 50 Twin. Thanks.

[Mchandler]

Did you do your own port work if so how much did take out

[camohunter]

Did you do your own port work if so how much did take out

I did not do the port work. Pete Nydahl in Wisconsin did most of the work on the block. I highly recommend his work. The ports were widened a good bit.

[camohunter]

This was done with a rotary file and a die grinder. I sanded and polished the surfaces after these were taken.

63087

63088

[Fastjeff57]

Kinda hit the carb bore a bit with the old grinder, eh? Too bad, but it shouldn't bother a thing.

Jeff

[camohunter]

Got my reeds in today. Boyesen Power Reeds. They don’t look like what I expected. They were my second choice after Chris Carson reeds. Chris would never return my call or text after the first time I spoke with him. A friend of mine tried to buy some after me and Chris wasted his time also . I guess Chris Carson has better things to do than sell people stuff. 63216

[camohunter]

I'm porting the reed block cages. I'm not sure this will prove to be a good idea. What do you think?

63232

[Tiller guy]

Did you use lock tite? I'm always worried the screws will come out and go through the motor.

[camohunter]

Did you use lock tite? I'm always worried the screws will come out and go through the motor.

Yes.

[camohunter]

6812368124

Finally got the powerhead on!!

Getting the Yamaha carbs to work right is yet to be accomplished

[camohunter]

68161

[camohunter]

68163

[Roflhat]

looking good

[quty06]

look fast

[camohunter]

71214

Update: My motor runs really good. It’s the best idling motor I’ve ever owned. I’m seeing speeds close to 50mph on my Edge 553 duck boat.

[camohunter]

I think you are right. From my research I found that the Yamaha 60 and 70 intake manifold and gasket is the same part number. That would seem to indicate that the carburetor throats are the same diameter. 70 carbs come with 145 mains. 60 carbs come with 140 main jets

I found out later that the 60 carbs have about the same bore as the stock Tohatsu 50 carbs. The 70 Yamaha carbs have a good bit larger bore.

[wmk0002]

Sharp motor! Did you change or mod the tuner?

[camohunter]

Thanks

I did change the tuner to the M50D tuner. This was originally a 2004 M40D2 motor. There are 3 tuners for this motor. M40D is the smallest, (M40D2 & M50D2 are the same), and M50D has the largest diameter pipe.

I did not modify the tuner in any way. I started to dry stack it and take the water out of the exhaust pipe, but decided I didn't want to risk possible long-term dependability by doing that.

Maybe someone who knows more about dry stacking can comment on this subject.