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Old 06-04-2018, 05:50 AM   #101
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Hey Roflhat, I am new to the forum. I am not sure if i missed it in your posts, I am inquiring about how you were able to switch the tiller handle from push to pull, or did you change something on the carbs? I am hesitant to order the newer style because of it. Any input on that would be great. I have a 91 70 hp 2 stroke, and am in desperate need of improving the tiller handle. Thanks
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Old 06-04-2018, 08:11 AM   #102
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 403
hey, I took it to a local fabricator who flipped on of the gears inside the tiller which changed it over from push to pull. Had to grind back a bit of the other shaft and weld another bit I think.
Discovered earlier this year that there's a guy who makes a kit to convert them, I'll dig out his details for you
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Old 06-04-2018, 05:46 PM   #103
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Yeah if you could that would be awesome, was there one specific model number of tiller handle you were aiming for in particular for that motor? I have the existing friction kit, but i can go any way with that
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Old 06-04-2018, 08:57 PM   #104
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 403
This is the place - https://www.facebook.com/traylormccoy/
Not used them myself but been told they make the kits, I imagine they fit most Yam tillers
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Old 24-04-2018, 09:40 PM   #105
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 403
Got some 15mm marine ply to make a new floor for the Zapcat, cut and sanded down, will have four coats of paint too. Does look good having the white and black boats together




Also got the crank for the second engine back, they forgot to weld it so had it welded locally, really nice job


Decided to build another 70hp short shaft, got the leg, transom bracket from a 60hp short and the cowling and pull start from a 60 Enduro. Looking for a 70hp gearbox and powerhead at the moment.


Spent tonight stripping my own engine to change the exhaust, fits well, had to cut 5mm off the tab on the flange. Bought some new carbon reeds from Boyesen to go in as well, hopefully the gearbox is back this week from blueprinting, would be nice to get out in it!
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Old 11-05-2018, 05:51 PM   #106
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 403
Sent the gearbox to Geoff at Ocean Racing to be reshimmed with new bearings etc. Got it back last week and got sanding the outisde, took a fair bit of metal from the skeg and a bit from the bullet too, not quite down to the homologation sheet but a lot slimmer than it was. Used filler primer to smooth it off and then 2 thin coats of silver on top.




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Old 13-05-2018, 08:46 AM   #107
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 403
Got out for a blast yesterday, was still quite windy around 20 knots. Engine is running the best it ever has, everything is absolutely spot on. Need to get my steering damper setup though, plenty of speed wobbles now I've removed the bungees. Very very happy with how it ran, got 50 knots with the 15G yamaha, which given the conditions is excellent.
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Old 14-05-2018, 05:04 PM   #108
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 403
Started putting together the steering damper, designed a bracket to mount the tiller to the cylinder. Also bought a bi-directional valve which will hopefully allow me to adjust the stiffness of the steering. Drilled out two of the brass connectors to allow fluid through
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Old 19-05-2018, 09:47 PM   #109
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 403
Got the damper setup finished off today, seems to work well but couldn't get out to test it

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Old 23-07-2018, 08:14 AM   #110
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 403
Not had perfect weather for testing recently but got a couple things done, re-bled the steering damper which is much for effective now. Bought 1m length of ali angle which I'm going to fit across the transom to strengthen it, credit to fel2 for the idea. Had some really bad weather last week so decided to go out anyway, excellent fun. Managed to break the throttle roller, I've now had another waterjet out of aluminium, pretty sure this one won't break!
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Old 30-07-2018, 08:26 AM   #111
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 403
Got the new throttle roller fitted, along with the 1m length of ali angle along the transom. Definitely an improvement, boat feels far more drivable in choppy conditions, especially with the steering damper too.


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Old 19-08-2018, 04:33 PM   #112
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 403
Got my other 70hp project up for sale - https://www.ebay.co.uk/itm/113201949134?
great start if somebody wants to build the ultimate thundercat engine
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Old 27-09-2018, 04:30 PM   #113
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 403
Had some cracking days out through the summer, got out for a run a while back 3up in mine and 3up in jacks, went into some of the caves and arches around Uig.

New drybag, all black of course


Weighed the boat and engine, with around 10l of fuel and the anchor, came in at 171.5kg. Just doing final preparations for Coniston next month.

Got a new helmet for it, courtesy of Douglas Curley at Eric Young & Co. who are very kindly sponsoring me.

Bought a dial indicator and used an old record with a degree wheel sticker to do the timing. Never managed to find a service manual for this engine but spoken to lots of folk, mine was at 21 degrees at WOT, now adjusted to 23 so will see how it goes. Been told I can go higher but dont want to go blowing holes in the pistons


Photo from last year
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Old 27-09-2018, 04:35 PM   #114
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 403
Some exciting development on the props I designed too, making decent progress with them. Should be ready for testing soon hopefully



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Old 09-10-2018, 12:33 PM   #115
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Country: Scotland
Location: Isle of Lewis
Occupation: Skipper
Boat make: Thundercat
Engines: Yamaha 70ces

Join Date: Apr 2014
Location: Isle of Lewis
Posts: 403
Getting a lot of testing done just now, different engine heights, propellers etc.
Got the first 2 Forge V1 cleavers back, one tuned to design spec the other tuned up to 19p and more lift. So happy with them, they run superbly and really fast. Awesome acceleration and still better top speed than the Mercury equivelents. Absolutely delighted with them. Having another 2 set up just now, one with less diameter and one with a "stealth" cut on the leading edge.



New helmet is super comfy too, think I'll start wearing this more often on the boat


A bit of weight reduction too, cut the steering bracket (only used on circuit class boats). Means I can trim the engine further in and also it weighed 1.8kg.
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