My Thundercat - Page 8

roflhat · 23-05-2020, 09:21 AM

Engine is running well with less timing, lots of testing done. Rebuilding again now though, due to one of the wee bolts from the choke flaps coming loose...

Tested the motorbike windscreen, worth about 0.57 knots. Modelling the boat on CAD too to try do some CFD aerodynamic tests. Not something I know much about

roflhat · 26-05-2020, 01:40 PM

Finally getting somwhere with the CFD. Took a long time to get a solid model in Rhino which I could use. Cd, drag coefficient is around 0.438, now to try and reduce it

roflhat · 07-06-2020, 05:44 PM

Now thinking simply rounding the front of the cowl a bit would help more than the windscreen I was using. Shape of the screen would generate downforce, which I don't need.
Backed the timing right off to 13 degrees, which seems to agree more with the pistons. Been out in the boat a lot since the lockdown was eased, no issues so far.

Ordered a 53L fuel tank as the 21L doesn't last long! Still plenty of testing to do, just waiting for dead calm conditions. Going to test the 90hp carbs again
Carbon cowling is coming along nicely, should be 3kg lighter than the original which was 5kg

roflhat · 18-12-2020, 10:33 AM

Bits and pieces done to the boat, got more props to try just need some decent weather. Gearbox is getting a nose cone added on so will have to re test props anyway

roflhat · 09-01-2021, 08:07 PM

Engine sadly didn't last long with the modified gear box...
Thinking it lifted too high, lost water pressure and cooked the top piston. Fortunately didn't damage the block so will get it back together soon enough. Going to remove the nose cone from the gear box, have ordered a low water pickup version which should solve the issue. Whos stupid idea was that anyway

Managed to quickly test the Forge V2 before the engine blew, very happy with how it went. Still got 5 more props to try but will have to wait a while. Going to do a couple other jobs on the engine while it's apart. Cleaned up the cylinder head, printing some new velocity stacks for the 90hp carbs. Might get some nylon engine mounts made up for it, and maybe a lick of paint for the leg.

roflhat · 15-01-2021, 09:25 AM

Doing some more bits and pieces, the play in the engine was from the swivel tube bushes. Getting some brass ones made up which should last longer. New stacks are made up, also designed some reed block stuffers. Took a few days and 7 versions to get them how I wanted but they're a really good fit.

Also cut down the air intakes on the cowling.

Going for 185/195/195 main jets to start with, playing it safe! Also drilled out the needle valve seats, they were 1.6mm now 1.8mm. Ordered a bigger fuel pump, from the Yamaha v6 two stroke.

Flowed the exhaust and sandwich plate, removed some restrictions from there. This does mean the engine isnt UIM legal any more but I don't mind. If I go to Coniston again it will likely just be for a performance certificate rather than a record. Would prefer to go for the worlds fastest thundercat.

Luvrbredten · 26-01-2021, 02:34 PM

great to see updates on your project

roflhat · 26-01-2021, 07:12 PM

Quote:

Originally Posted by Luvrbredten

great to see updates on your project

Thanks! glad you're enjoying it

gazza · 27-01-2021, 05:50 PM

Good to see your still modding your boat, Talking to Davie Anderson the other week and you came up in disscusion.

roflhat · 27-01-2021, 10:15 PM

Had Davie and a couple of his mates out for a quick spin last summer, not in the thundercat! Met him a couple of times before that

ollyit · 08-02-2021, 07:27 PM

loving your work mate,

ollyit · 08-02-2021, 07:27 PM

where did you get your after market head gasket from for the yamaha? the one that was a bit thinner than the genuine yamaha one please?

roflhat · 09-02-2021, 09:20 AM

Glad you're enjoying it!

Recmar I think make the gaskets but I avoid them now. Seemed to be causing some issues with water into the cylinders. Maybe OK on a standard engine but can't say I'd recommend them

ollyit · 11-02-2021, 07:06 PM

thanks mate, best stick to genuine then

roflhat · 10-03-2021, 01:57 PM

Engine is now back together bar the gearbox with new LWP which should hopefully be done next week. This kit seems to fit the 70hp gearbox better too

Got new nylon engine mounts made up and brass swivel tube bushings. Everything went back together nice and snug, far nicer than the old plastic ones. I did machine grooves in the brass sleeves like the plastic ones for the grease

hcottle · 21-03-2021, 02:38 AM

Good read mate!!

roflhat · 22-03-2021, 10:31 AM

Quote:

Originally Posted by hcottle

Good read mate!!

Thanks

roflhat · 22-03-2021, 07:22 PM

Spent far too many hours on this... New design of head and a fancy cover plate. Going to see if I can get one CNC'd

roflhat · 04-04-2021, 09:37 AM

Finally got out for a run and some testing yesterday. Gearbox isn't properly painted yet so it's back off for that now. Engine running beautifully and stayed that way which is always nice!
Speeds are up about 1.5 knots on average per prop from the last test. Plan now is to remove some weight from the boat, carbon cowling, replace the grabner lifejacket with a formula which is 1kg vs 2.2kg. Then the billet cylinder head and maybe try lift the engine up some more

Head is finished and should be here next week

Been thinking more and more about switching to an Aquarius hull just can't bring myself to spend the money...

Luvrbredten · 07-04-2021, 12:26 AM

Wow. Looks beautiful on water. I can imagine how smooth it went.