Yamaha Thundercat engine repair

Despair shop Part 10 – hole-y smoke!!

Yamaha Thundercat engine sumpThis week I acquired a nice old Suzuki Bandit that somebody had attempted to modify and basically fucked up beyond all recognition. It looked ok but it wouldn’t start – hell, it wouldn’t even turn over so it was a big old gamble. Someone had altered the wiring at the front and made a right old dog’s dinner of it. There was a big bunch of wires cut off that looked like they should be the ones going to the instruments but they were all the wrong colour. I knew it was going to be time consuming but as it’s only electrickery I thought it would be relatively simple. Needless to say, not for the first time in my life, me and reality were a long way apart.

Any normal person would get the manual at this point but I am so impatient I thought I would just scan the interweb and find the appropriate diagram – which turned out to be a lot harder than expected – no I don’t want to sign upp for free for the first month only then just 14.99 per month when you haven’t got what I am looking for anyway.

I had a couple of diagrams for earlier bikes but there seems to be two instrument packs for the later bikes – one has an LCD panel in the tacho, mine doesn’t. Mine has 14 wires, some others have more, some less. I still haven’t found a diagram that matches mine so I had to set about experimenting until I had identified the function of every wire. I now have to find where those wires are on the bike, which is where the real challenge begins.

In the mean time I put some finishing touches to my CBR1000F – the engine is all sorted, oil and filters changed – the air filter was particularly grubby and had clearly been neglected for a number of years. I suspect it was making her run rather rich – they are only a few quid but I guess with them being tucked away behind panels people just don’t think of them and don’t bother changing them.

I also got a replacement genuine Honda mirror to replace the non original hideous thing on the right hand side. Just waiting for a couple of Dzus fasteners now and it will be ready for MoT.

The other thing that happened upon the shop of despair was a very nice Yamaha Thundercat, at first glance it was hard to see anything wrong with it. The bike had clearly been looked after – it was pretty much spot on and not covered in 10 foot of crap, which made a nice change. Upon further inspection though I found what can only be described as a massive hole in the engine casing. The broken bits were still in there so it looked like it has hit something hard enough to bust the ally housing. It was far too good to break so I looked at options for repairing it.

Welding wasn’t an option as I don’t have TIG and didn’t have time to learn on the job as it were. On searching on tinterweb I read bout people having good success with high heat JB Weld so I thought I would give it a try. As it was a big hole I used stainless steel mesh to strengthen it up.

Cleanliness is critical at this point so everything was cleaned several times with degreaser and finished off with a good rub with coarse wet and dry to give a good key – I went well beyond the edges of the hole to make sure I had the best possible key. I used two separate products – both from JB. The first was a high heat high strength epoxy resin – it’s two part and as strong as anything I have ever found. I tested it first on a piece of scrap ally and it had amazing strength and resists oil, petrol and heat so it’s ideal for the job. I used that to stick the mesh to the engine.

Yamaha Thundercat engine sump - repairedI then used tome two part putty that is also an epoxy substance, it dries incredibly hard and once it’s set it ain’t coming off. It was very easy to work and form to the shape and it pushed nicely in to the stainless mesh. If you are doing a job like this always drop the sump and make sure 100% that  there are no bits in there that can ruin your life at a later date. There were plenty of bits in mine a good thorough clean followed and it was spotless when put back in place with a new gasket, of course.

I went rather over the top with this stuff as I wanted to make sure it was never going to come off. I highly recommend this method, the stuff dries incredibly hard and is resistant to heat changes, I tested the stuff extensively before going with it because I was very doubtful but it really is amazing stuff. Once dry it can be drilled, tapped, filed and made a lot prettier than in the photo above, sadly I appear to have lost the last photo of when it was finished but you would be hard pressed to spot it, it dries to a very similar colour to the surrounding material. It is good for temperatures up to 450 Fahrenheit so way more than the engine will ever get to at this point.

Article provided by David Powell of Boston Bike Bits.

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