Simplex cylinder top cover

[sanddancer]

Hello all,

I just bought a part built Simplex, and ran it on compressed air yesterday. The left cylinder top cover was leaking, so I stripped it. The front outside bolt hole is stripped,as the cheese headed screw BA4 was too long, and the screw had bottomed. This is the worst place possible for this to happen, as there is no adjacent bolt, with the slide gear below. The only choice that I can see is to drill & tap BA3, but it is very near to the slide gear. I remember when I was younger seeing screw thread inserts, but know nothing about them. I imagine they may not supply such kit for small threads, but can anyone recommend another course of action, without having to buy a new cylinder,

regards,

George

[ron]

Hi George, welcome to the forum.
I've just had a look at mine and I don't think you would have any problems tapping it 3ba, the hold down studs in mine are 5ba by the way.
If you can find a supplier of Helicoils small enough for your purpose I would recommend them, I've used UNF ones for classic car resto and they are excellent, if anything you end up with a thread stronger than the original and they are very easy to install.
Ron

[russell]

Hi George,

As Ron said, there should be plenty of room to tap 3 BA. However you should use studs and nuts rather than screws to prevent wear on the threads in the cylinder. You could always make up a stepped 3 BA / 4 BA stud to keep the hole in the cover the same size as all the others.

I can confirm that Helicoils are excellent for vintage car engines (I have used bith WW and BSF sizes) but the special taps are very expensive for a one off.

Russell.

[sanddancer]

Hi Russel.

I thought that studs would be better when I opened her up yesterday, but the chap who built her is 90 years old now, and things may have changed. (This is my first steam model) Your suggestion seems sound, and I think that I will take it on-board. Many thanks for that, & I look forward to exchanging info with you in the future,

regards,

George

[lancelot]

Hi George, as Russel said ...I would go for the stepped stud for the repair, and fit studs to the others instead of using screws...I think even if you were able to obtain Helicoils of such a small size you have to go at least two sizes above the needed size to fit the Helicoil in the first place...
All the best for now,
John.

[sanddancer]

Hi John,

what you say makes sense to me. Thanks for your help,

regards,

George