My thundercat - Page 8

Roflhat · 21 June 2015, 19:48

Had an eyeball of the 90 chestplate and I don't think it will work. The bolt holes aren't in the same place.
Changed the reeds over, it already had carbon reeds, don't know what make they are. Compared them to the racing CCM reeds, which are much thicker.

Also cut out part of the bottom cowling which was in my way,

hopefully now I can get a set of stacks on.

I left the carbs soaking in the parts washer, probably have to strip them down to free off the throttle and choke.

Still to do:
change gear oil
get a tiller and make it work
just waiting for the pull start and cowling and I can fit them
fit old merc damper

Roflhat · 24 July 2015, 09:34

Wee update, got the cowling and pull start on, looks massive now! Need to remember to weigh it before it goes on and compare it to the tohatsu, I don't think there's too much in it.
Think I'll take the tiller over to the local fabricator and see if he can work something out, struggling to find a suitable replacement.
Here's how it looks just now:

Roflhat · 26 July 2015, 18:35

Got the motor running today, carbs were absolutely filthy so they're all cleaned up now, new iridium plugs in. Was having issues getting it to change gear so gearbox came off, now all sorted. It runs really well, very very hard to pull over! Still need to change the gear oil

Roflhat · 18 August 2015, 22:14

Got some more work done on it, runs fine on the muffs but when on the water and in gear it won't take revs. Checked the spark plugs and coils are all fine. Checked the carbs and they are full of gunge again, thinking the fuel lines must have been filthy.
Linkages are all done, don't think it's quite getting full throttle but won't know until I've been for a run with it. Got the mercury chopper on it just now.
Engine is on the boat now, looks massive!

1eyedjim · 19 August 2015, 18:44

Looks mint. Interested to hear how fast it goes

lukewhiting · 19 August 2015, 22:40

What are you planning on doing with your 50??

Roflhat · 20 August 2015, 09:31

Quote:

Originally Posted by 1eyedjim

Looks mint. Interested to hear how fast it goes

Cheers, so am I!

Quote:

Originally Posted by lukewhiting

What are you planning on doing with your 50??

I'm doing a swap with my mate so he'll get my modified 50 and I'll get his standard 50 plus cash. Means I can keep tuning the tohatsu as well. TSR billet head for it next I think.
If you know anyone interested in a tohatsu 50 let me know, it has boyesen reeds, nukaru coils and might come with velocity stacks.

Roflhat · 24 August 2015, 10:24

Having some trouble with the yamaha... Seems to be running fine on the muffs but when I put it in the water it won't take revs in gear and just dies. So I tried it yesterday with the choke fully on and the engine much preffered that, even got the boat to plane. So I'm thinking an air leak somewhere? Checked the carbs and reed manifold and they all seem fine. Going to take them off again today. Also going to remove the flywheel and make sure there's no rust beneath it.
Any ideas??

1eyedjim · 24 August 2015, 13:46

Probably not possible with with the power head fitted but wondered if you can pressure test the engine to find the leak.

Roflhat · 10 September 2015, 09:18

After a lot of fiddling the engine is going a lot better. Still not perfect so I think I'll rebuild it when I'm home in the winter. Just all new gaskets and seals, and weld the crank while its apart.
Got it out for a quick spin the other night, didn't stray too far from the pier incase it broke down on me! Managed to spin the 15p worked SOLAS to 7380rpm. Not sure on speed but I reckon it was around 50knots. Going to hopefully try it again and take the GPS, wasn't expecting it to work well enough to need one last time.

Roflhat · 10 September 2015, 20:27

Was out again tonight, had the same 15p worked Solas on. Span it to 6600 1up at 48.9 knots, had a lot more in it but couldn't hold it flat out as it started to porpoise. 2up managed 7380rpm at 54.7 knots, the fastest I've gone so far and with an all round propeller. The bigger props should go a lot harder.
I think the plan over the winter when I come home is to rebuild the powerhead with all new gaskets and seals and get the crank welded.

Roflhat · 11 September 2015, 12:10

Couple of photos:

A few props have been added to the collection:

got the steering damper setup today, it's just an old rusty Mercedes one

Roflhat · 11 November 2015, 10:47

Couple of updates, even though I'm away been gathering some nice parts for the boat.
A pair of new props:
11.75x23p OMC Overhub cleaver

12x23p OMC Overhub cleaver

TSR billet cylinder head, the first one made for a Yamaha 70 so I'll be the guinea pig

Squid Boat · 12 November 2015, 02:32

Great thread, thanks.

Cheers

dave3235 · 12 November 2015, 07:07

Hi

What benifits are you are you expecting from the head,any plans on a blited
Crank or is there no point.

Roflhat · 12 November 2015, 09:27

Quote:

Originally Posted by Squid Boat

Great thread, thanks.

Cheers

Glad you enjoyed it!

Quote:

Originally Posted by dave3235

Hi

What benifits are you are you expecting from the head,any plans on a blited
Crank or is there no point.

The new head has a positive squish band, the CES head had negative squish (not too sure why), so the combustion chamber shape is greatly improved. The same design has been used on tohatsu 50's with good results, over 1000rpm gain on some engines. I'm not much of an expert on cylinder heads but I've spoken to a few guys who are and they reckon this is the way to go.
A lot of guys machine the standard head to give it positive squish, but a re-designed head is even better. Another benefit is that it doesn't use gaskets, but O-rings instead.

Not sure about the crank, once it's welded it's strong enough for all the RPM this motor will see. I was thinking about designing a custom flywheel, but making it too light gives jittery idle. The top speed isn't usually affected, just acceleration.

two stroke mick · 12 November 2015, 11:52

That head looks too pretty to use on an engine. It looks like a very fine bit of workmanship. What sort of money does it cost to get such a head made up. Not needing one just nosey

TSM

Roflhat · 12 November 2015, 11:59

Quote:

Originally Posted by two stroke mick

That head looks too pretty to use on an engine. It looks like a very fine bit of workmanship. What sort of money does it cost to get such a head made up. Not needing one just nosey

TSM

I was thinking the same, shame to put the cowling on now! My mate got one for the tohatsu 50 (the one in this thread) too, so lots of testing needs to be done.
It was $535 Ausd before shipping, around £250. The tohatsu ones are a wee bit more expensive, $720 each because they come with a billet thermostat cover too. Shipping for both the heads was $205.

Roflhat · 17 December 2015, 12:54

Got home a couple days ago, stripped the engine down. Looks like one of the centre main bearings on the crank has had it, which is apparently quite a common problem on the Yam 70. So I've now bought another 2 complete powerheads, hopefully one has a decent crank in it. Was also given a 60hp head, unfortunately turned out to be a merc or mariner, non-removable cylinder head. Was looking into having the bearing replaced, maybe have the crank dynamically balanced while it's being done, but its pricey.
Put the back half of the powerhead together, TSR head is on, all new gaskets and seals going on. Just doing welded crank and TSR head for now. You can get pre-ported liners for £145 each, maybe build up one of the other power heads with mod parts

You can see the difference in head shape here, this is the original CES head

Roflhat · 17 December 2015, 13:03

This is a side project I'm working on for Uni, modifying a surface piercing propeller. I sent the propeller to a company who scanned it and created a point cloud. It's based on an 11x18p Mercury Cleaver. Got the IGES file back a few days ago, here's a couple screenshots from Rhino

I've bought a 13 spline RUBEX hub which I'm going to use as a reference to model around, I'll start modifying the design hopefully towards the end of January