View Full Version : What material to use for these?

06-23-2012, 02:09 PM
Cylinders for a Bryce Berger 'Handraulic' engine starter


50mm bore.
The one on the left is probably original from 1947, when they were made in France by Berger. Later amalgamated into Bryce Berger in the UK, which in turn became part of CAV. These are still made, the one on the right is brand new.


The trouble is that, being French, the original starter was all metric. Later the design was updated in the UK, & while they stuck to the 50mm bore most of the other dimensions and threads were changed to Imperial. The one on the left has a 60mm x 1.5 thread, the new one on the right has a 2.375" x 18 tpi thread, at the far end. nominally 0.3mm bigger in diameter. The Metric spares are no longer made. There's a plug which screws into the end nearer to the camera, which carries a male thread to hold a cover and a female for the oil input. The new ones have a much bigger plug thread than the old, but I could probably buy a new plug if I didn't fancy making a new one. One reason why the cylinder is scrap is that the thread for the plug has galled badly.
It's very tempting to rethread the new one with the metric external thread, but it might then not be strong enough. It screws into the cast aluminium body of the starter, and working at the maximum 4250 psi there's a theoretical maximum pull on the thread of 13000 lbs.
Simplest & safest bet will be to make a new cylinder, but I'm interested in recommendations for material. I probably have some EN8 (1040) in about the right size, but wonder whether I might struggle to get a good enough finish on that. I can ream & hone it after boring.



06-24-2012, 12:13 AM
You better get you a piece of 4130-4145 alloy steel with 110K minimum yield for that part. Don't know off hand the EN or BS number for this grade in UK. EN8 I don't believe has the strength needed. The higher yield alloy material will finish out nicely. That looks like a honed finish on that ID. Also, the part has a maganese phosphate coating, not that important but just for info.

Jaakko Fagerlund
06-24-2012, 05:11 AM
It will hold easily, no matter what the steel grade is. Even a 1/8" pipe thread will hold a 600 bar (roughly 8500 psi), pipe nipple being steel and the threaded part being cast iron.

Just don't make the threads to their sloppiest limits :)

06-24-2012, 11:06 AM
Honed ID cylinder tubing which is SAE 1020 or 1026 would be what I would use assuming that size was availible.


The other option would be to degrease,clean bore,weld up and remachine the threaded end.The fact that it galled is a good indicator that the part isn't treated.

John Stevenson
06-24-2012, 12:25 PM
Open the existing thread up until all the galling is gone [ or most of it ] then make a new plug to suit.

Don't make a meal out of it, work smart.

06-24-2012, 02:13 PM
Open the existing thread up until all the galling is gone [ or most of it ] then make a new plug to suit.

Don't make a meal out of it, work smart.

Might be an option, but the reason for stripping it down was rust in the bore. I'll hone the bore first to see how well it cleans up, but not too hopeful.


06-25-2012, 03:38 PM
Definitely scrap, there's some severe pitting evident in the bore after putting ahone through it. I know the thread strength shouldn't be a major issue with choice of material, after all the female thread is into cast aluminium. I seriously doubt that it would be strong enough to be safe if I simply rethreaded the new cylinder with the metric thread. Tempting though!


06-28-2012, 03:29 PM
I got word from the horse's mouth today, that the proper material was EN8M,Normalised. The M is a free-machining variant, didn't know it existed!

Anyway, I approached the job from a different angle, decided to make use of the new cylinder I had to hand (and the old one).
I bored out the section of the scrap cylinder with the long external thread, to the point where there was just enough meat to cut an equivalent internal thread. Then turned down & threaded the end of the new cylinder to fit that internal thread:-


Then degreased & loctited this threaded sleeve into place, & trimmed it up in the lathe. Of course it was important to remove the minimum of metal from the new cylinder, because of the pressure it carries when in operation, but this is the 'full stroke' end of the cylinder so the pressure will be substantially reduced by the time the piston reaches this end.

Then I had to make a new 'cylinder cover', this had to be threaded 2.125" x 18 UN form to screw into the cylinder. M30 x 1.5 to take a nut for the alloy cover (which also holds the return spring for the opposing cylinder), M16 x 1.5 right through to take a hydraulic fitting at one end (luckily I had a tap for that), and an adjustable piston stop at the inner end. It also has to have 4 holes for a key to screw/unscrew it into the cylinder:-


Next problem was I needed a copper washer to seal the plug into the cylinder. I had a piece of 2.25" copper bar, but it wasn't quite big enough diameter. I 'set up' one end after initially boring it, then was able to machine it to the size needed:-


This pic shows the main constituent parts, to give some idea how the thing works:-


The two pistons are attached to racks which work either side of the central pinion. The idea is that when the oil is released from the gas spring into the cylinders, they rotate the pinion as well as pushing it forwards. It has ratchet teeth on the face, which engage with a similar ratchet mounted onto the front of the crankshaft. It's supposed to give the crank 2 and a half revolutions. If the engine doesn't start, you then have another five minutes pumping up the oil for anther go!

Tested tonight on the engine & working.

I probably saved a bit of time, relative to making a new cylinder from scratch. I might yet have to make one or two new ones, as this was a 'spare' starter being brought into service so that the one previously on the engine, which is leaking very badly from the cylinders, can be overhauled.

Incidentally, before starting the job I did check whether a new anticlockwise starter could be supplied, not surprised to learn that it couldn't. A new clockwise starter is priced at 1800 stg (somewhere over $2500 usd), for the starter alone. The gas spring, pump, and reservoir are all extra.


10-10-2012, 10:48 PM
Id use B-7 (4140 type

John Stevenson
10-11-2012, 05:10 AM
hat was 4 months ago.

Been , gone and dusted.