My thundercat

[Roflhat]

Boat and engine have been going really well lately, spent a lot of time cruising around here. Spent today fitting the primer kit in place of the chokes, haven't tried it yet but hopefully it should work well.


Should allow improved airflow as well, gives the air a clean channel down the carb throats


I also designed a new roller for the pull start, the old one was a bit worn!

[Bchstrevor]

Really enjoy reading your post on here and scream and fly Roflhat you've got a very very sweet setup. Going to build my m50d2 based of yours, appreciate you taking your time and posting makes it much easier to process the steps involved! Ps your fabrication skills are very impressive... I'm only a little jealous

[Roflhat]

Originally Posted by Bchstrevor

Really enjoy reading your post on here and scream and fly Roflhat you've got a very very sweet setup. Going to build my m50d2 based of yours, appreciate you taking your time and posting makes it much easier to process the steps involved! Ps your fabrication skills are very impressive... I'm only a little jealous

Thanks very much! Glad you're enjoying it, the tohatsu is still going strong, my mate Jack has it on his Zapcat now, we're getting 54.9 knots from it with the 18p chopper with great acceleration too. The problem with having an engine that works well is that I have nothing to fix, the idea of a short shaft Yamaha 90hp is sounding tempting...

Let me know if you make a thread of your build, good to see how other get on with these motors. What boat have you got it on?

[fel2]

Just wondering what propeller would you recommand me
For a 30HP 2 stroke engine ?

Thank you

[Roflhat]

Originally Posted by fel2

Just wondering what propeller would you recommand me
For a 30HP 2 stroke engine ?

Thank you

Depends what you're after and what sort of engine it is. Do you know the gearbox ratio?

Assuming it's 10 spline
For the tohatsu/mariner/mercury 2 cylinder 2 stroke an 18p mercury chopper would be a great high speed prop. We had a 10x15p chopper on my old Tohatsu 30 on the surfcat, went really well but could have done with more pitch.

For an all round prop I'd be looking at a 13p stainless steel prop, possibly a quicksilver 10x13p.

[Roflhat]

So unfortunately looks like my photos can't be seen any more, photobucket wants $399 a year to host them... If I have time at some point I'll try upload them to a new site and edit all the posts

Recently changed the head on the Yamaha, removed the TSR one and found it was letting in water


so I've stuck the original head back on, performance seems about the same but waiting on some flat weather to get top speed figures. The old head isn't in great condition, if anyone has a spare 70ces head kicking about please give me a shout!


Also found that there was some flex in the transom, more than I'd like so I had another jack plate waterjet cut, 12.7mm thick so I could countersink bolts and have the plate flat against the transom which should reduce the flex. Also had some pull handles cut using the spare ali, these ones are a wee bit too big to fit through the cowling unfortunately so I'm having another made.


Tried the original 70hp carbs on, the engine just won't run properly with them, feels like it's running on 2 cylinders. I've rebuilt the carbs with new gaskets, cleaned the jets with carb cleaner and the airline and the jets are immaculate, so not sure what it could be. Also very hard to start with them, put the 90hp carbs back on and it starts easier and runs fine

[watersidemat]

Roflhat, going back to page 3 of this when you took the ring gear off the fly wheel, did you have to cut around in a circle or just one cut down and it comes off? How is it secured to the fly wheel? Mine's off at the minute so might be worth cutting mine off.

[Roflhat]

Originally Posted by watersidemat

Roflhat, going back to page 3 of this when you took the ring gear off the fly wheel, did you have to cut around in a circle or just one cut down and it comes off? How is it secured to the fly wheel? Mine's off at the minute so might be worth cutting mine off.

You just have to cut down, then the outer ring pops apart. I haven't done the same on my Yamaha, although I might lighten the flywheel and rebalance it. On the Tohatsu it made the idle quite jittery, if you spend a lot of time at low RPM or idle I probably wouldn't recommend it. It's just pressed onto the main flywheel hub

[Roflhat]

Had some excellent weather last week, got out for a spin and got some footage with the drone
https://www.facebook.com/seumas.macl...72511886123442

[jeffstevens763@g]

Originally Posted by Roflhat

Had some excellent weather last week, got out for a spin and got some footage with the drone
https://www.facebook.com/seumas.macl...72511886123442

Nice one great video what speed did you top out seumas

[Roflhat]

Upto 52 knots in that video, was only running a small 15p modified Yamaha semi cleaver. Great prop for playing around with, loads of grip and never cavitates but also I asked for no cup, so there's no torque steer

[Roflhat]

Not got out in the boat so much lately, getting into winter now.
Had the original cylinder head reconditioned, looks really good. Interestingly the genuine Yamaha head gasket is around 1.4mm, the aftermarket one is 1.2mm so might increase the compression slightly.

Trying to get the engine to work with the standard carbs too, it just isn't happy with them, won't idle and it feels like it's dropping onto 2 cylinders. I've now had them put in an ultrasonic bath so I'll try them again. Designed another version of the throttle roller as it still wasn't getting WOT with the standard carbs. Unfortunately the roller broke when I twisted the throttle, so having another made in a harder material.

Looking at having the flywheel lightened too, not by much. The homologation sheet for the 70ces says 3800 grams so I'll take it to that, it will obviously be heavier due to the pull start attachment on the top. I'll have it balanced too, I suspect it's fairly well balanced from factory but won't hurt to have a finer tolerance

[Squid Boat]

Sweet.

Cheers

[Roflhat]

Got the engine running yesterday and out for a run. Starts a lot easier now and runs smooth with the standard carbs and head which it hasn't done before. Throttle isn't opening fully yet - waiting for the new throttle roller to arrive.
New trailer arrived last night


Photo of some of my props


Did around 26nm yesterday, was nice weather but the throttle grip is still far too slippery so I removed the rubber section and designed a new one

hoping to have it 3D printed in ninjaflex which is pretty rubbery and flexible

[Livid]

holy crap, that's rapid. Good to see some other rib enthusiasts big on 3d printing. early this year i built my own delta printer from printed parts (the benefits of still being at school ) I've used it to do parts for my searider and my dad's weekender. P.S. i'd print that the other way up, so if the ninjaflex can't handle the overhang (it's a very difficult material to print tall) you still have a useful part

[Roflhat]

3D print turned out really well, the grip feels really good. Very flexible too, just like the original rubber part but far grippier.



Got another throttle roller, made of resin so should be a lot stronger. The surface finish is completely smooth too, very nice piece


Bought this prop, was last used on an offshore racer with a Yamaha 60DES in the 80's. Looks sort of like a Hoss cut chopper, says 11x20 on it but measures closer to 10.5" diameter. Should go well on the Yamaha, possibly even better on the Tohatsu which seems to prefer overhub props

[Roflhat]

Had the flywheel balanced over the winter, I assumed it would be pretty well balanced from the Yamaha factory. This is what I got:

"Your setup is 14.2 gm 25mm on the left plane. That creates a centrifugal force of 25.4kg at 8000rpm.
Taking it down to 2gm 25mm reduces centrifugal force to 3.5kg @ 8000rpm."


Got some new props, lots of testing to do

also looking at blueprinting the gearbox, maybe have the gears balanced like the flywheel. Might also go over the outside of the gearbox, make it more streamlined

[Roflhat]

There's a new surfcat up here too, same guy who bought the thunderbolt. He's now sold the thunderbolt and bought this instead, brand new Yamaha 40hp 2 stroke on it.

[fel2]

Nice !!

[69cmw]

Originally Posted by Roflhat

There's a new surfcat up here too, same guy who bought the thunderbolt. He's now sold the thunderbolt and bought this instead, brand new Yamaha 40hp 2 stroke on it.

What size is the surfcat? Does it have a solid transom?