WeeTed

I have posted this thread on another forum so I apologise if you are seeing this twice or have already answered.
I was given a very generous gift of a Taipan Tyro 1.9cc diesel. Its missing three of the four screws that connect the cylinder liner to the crank-case. Can anyone advise of the correct size and type required?
Any information on the engine would be appreciated. It could be an early model (but it does not have a prop nut so I don't know if it was meant to have a plain or a spinner type prop nut). It has plain aluminium coloured cooling fins.

I have had some good feedback so far and understand that I might need to use a 5-40 UNC Cap head screw (and reduce the head diameter) or that 1/8 Whitworth might work.
Some have used Loctite on the original screws but I only have one of these screws so need replacements.
The one that was in the engine has the following measurements: 9.06mm in length (overall) head is 4.13mm Diam and the thread diam is 2.4mm (over the threads).
Any suggestions would be appreciated

qazimoto

My Feedback: (1)

Eric,

sorry I should have mentioned on the other forum that replacing the self-tapping screws with originals doesn't usually work out very well. They loosen up within a few runs and allow the cylinder to rotate whilst running. Burford did sell a slightly larger diameter screw replacement self-tapper for the 2.5cc engine. The chances of finding these are vanishingly small. Never-the-less the screw you have looks like a 4:40 self tapper.

To use the remedy I've suggested you do need to drill out the existing crankcase hole, tap very carefully with a 5:40 UNC or 1/8" Whitworth thread, and use a suitably shortened parallel threaded screw. Cap headed (aka Allen key socketed) ones work well if you reduce the head diameter until it clears the cylinder. The screws I have (UNBRAKO brand) easily respond to a fine file or a sharp lathe tool.

I use a 1/8" Whitworth tap, and a 5:40 screw. The two threads are identical except the thread angles are 55 and 60 degrees respectively. My reason for mixing the two are simply because I have a set of 1/8" W taps, and 5:40 socket headed screws are easier to get c/w Whitworth.

WeeTed

Thanks once again and I now understand your previous advice. If I have to drill out the existing threads must I use a whitworth tap or is there a suitable metric equivalent (just to make it easier to get screws)? Cap / socket head would seem to be very sensible.
I dont have the equipment to do this work but will find a local engineering company who can do so.

qazimoto

My Feedback: (1)

The original Burford self tapping screw (there's probably a technical name for them) had a thread pitch of 40. Both 1/8" Whitworth and UNC 5:40 also have that pitch. That's why they're suitable. Isn't there a chap called Mike Crisp (sp) in the UK who does model engine work?

Edit: Apparently Mike is still doing engine work. I don't know his contact details except that he sells on ebay under the name "popular1956". He's probably your man. Good luck!

WeeTed

Thank you gazimoto. I have contacted Mike Crisp, as he did a repair to a Mills throttle for me last year (Top man). I had forgotten that he did repairs so thanks for the reminder.

WeeTed

Well the Tyro has been repaired. Mike Crisp did the work and told me that the original screw which was with the Taipan was a slightly undersize 3-48 so he was not surprised that the originals were prone to coming loose. As the holes in the cylinder flange were drilled very close to the edge of the flange and it would not have been possible to enlarge to .125" for 1/8" or 5-40 as was discussed above.

He has managed to enlarge just enough to fit the 4-40 screws. These screws had the head o/d reduced slightly and re blacked. He also made new gaskets and a spinner for it.
I am always impressed with the work which Mike does and can recommend him to any forum members needing some work done to a engine.

Now we need to get it in the air!!

I was hoping to post a picture, however, I am not allowed to post "URL's" as I have less than 10 posts so pictures will have to wait!

qazimoto

My Feedback: (1)

A good result finally. Well done :-)

WeeTed

Although these Tyro engines are an entry level type and not particularly valuable, they are not common in the UK.
I love to see these engines get a new lease of life rather than being left to languish in a spares box!
I will bench run it and post a video soon.

WeeTed

Photo Courtesy of Mike Crisp