My A J Reeves Bolton Triple Expansion Engine

[Del_61]

Re MECH, thanks for that, it makes sense. I did join around 6 years ago and stayed 3 days when I asked a technical question and I was bombarded with demands to show my work ...never went back

Sorry to hijack this thread.

The triple build is looking great by the way !

Regards

Derek

[Dalboy]

Really is starting to take shape and looking like a triple expansion engine, even though there is still a way to go yet

[simplyloco]

Pistons
These are in two parts to accomodate the 1/4" wide rings, thus avoiding expensive breakages! Straightforward enough providing one takes it steady!
Some pics.
This is what is wanted, a few thou oversize to permit final turning when pinned together.



Chucking pieces are provided, and I could have machined most of it this way round, but in the interests of accuracy I turned it round and turned an accurate chucking piece.


This way round, once again using the big tailstock chuck to position the piece in the three jaw, thus avoiding pfaffing about with the 4 jaw!


This is the outer face of the piston.


Turned round and faced, drilled and reamed.


Chucking piece sawn off and lightly held to finish the face. If I was doing lots I would have made a split shell, but not worth it foe a one off.

[crueby]

Nicely done - doing them in two halves is clever. I've seen it done on full size engines, never noticed it on a model before. 

[simplyloco]

More on the Pistons- going for Viton rings!

I've decided that I don't care what the rivet counters might say,  I'm not going to the trouble of making eccentric brass piston rings!
Although I wasn't trained in the use of O rings, I've done some research and it looks to me that Viton rings are the way to go.

As I've been a little cavalier -i.e. careless - with the bore sizes I thought that I would have trouble finding suitably sized rings. Not so! Dr. Google found me Simply Bearings,  a Company that I have used before for other bits, and they have a MASSIVE range of Viton rings, and I've managed to order three pairs of rings which match the three bores exactly. I've left the chucking pieces on to await the arrival of said rings.



https://simplybearings.co.uk/shop/Seals-O-Ring-Seals-VITON-O-Rings/c19_4501_4706/index.html?selection=VITON+Rubber+O-Rings

[RReid]

I don't think you'll regret using Viton o-rings. Like quite a few others, I've used them in live steam, compressed air, and IC applications, not to mention the fuel cells I used to build in my working life, all with good success.

[crueby]

Here in the US I've found good selections of the viton rings at The O Ring Store online, also amazon also has them, bags of 25 or 50 often.
When trial fitting them in the cylinder to check the groove size, put a drop of oil on the ring to get the best test, otherwise they can be grabby at first.

[Jasonb]

I've went over to Viton rings a few years ago and find they work very well

Just watch your groove sizes as for model use you don't want to compress the rings as much as most makers published data as we are not running at 20bar and the more the ring is compressed the more friction you will have to overcome.

And on the subject of friction you will only need one ring on each piston not a pair.

As an aside do the build articles mention why the small relief is cut into the mating faces of the piston? I can't see much point in it being there at such a shallow depth, Could be taken out deeper to lighten the piston as many a full size one was either in two parts or a core used to cast single piece ones hollow

[simplyloco]

I've went over to Viton rings a few years ago and find they work very well

Just watch your groove sizes as for model use you don't want to compress the rings as much as most makers published data as we are not running at 20bar and the more the ring is compressed the more friction you will have to overcome.

And on the subject of friction you will only need one ring on each piston not a pair.

As an aside do the build articles mention why the small relief is cut into the mating faces of the piston? I can't see much point in it being there at such a shallow depth, Could be taken out deeper to lighten the piston as many a full size one was either in two parts or a core used to cast single piece ones hollow

Thanks for the info Jason. Tubal Cain - the real one- recommended, for a 2.4mm section ring, a groove width of 3.2-3.4mm and a depth of 1.97-2.09.We shall see as modern wisdom suggests less 'pinch', i.e. greater depth, or even 'loose'.

A relief (0.0005")  is suggested to ensure the piston faces are in full contact.
John

[Jasonb]

Although I have built a lot of engines with metric rings I don't use his sizes as they give a lot of compression., he only gives one value which I think must be SAE I tend to use a pro rata size base on teh ME column for imperial rings

Nearest imperial is 3/32" nominal which is 0.103" actual and he gives a depth of 0.098 which is 5% compression

Using that for a 2.4mm metric ring 5% gives 2.28mm say 2.3mm, width would be 2.6mm

I have used this size on my published engine designs and not had any complaints when others have run them on steam or air. And it is what I use on my numerous "series 24" engines

[simplyloco]

Thanks to Jason's advice I managed to get three pistons down the bores without using my half tonne arborpress!
I remade the HP piston as it was unusable with the Viton rings, but the other were easily adapted by machining a rebate in just one half of the two piece piston.


I won't bore you all with repetitive stuff, but they now look like this! I made the piston rods today as well, having shortened them a bit to 'adjust' an earlier fubar...

[simplyloco]

Crankshaft looks OK.



I'll do the Loctite bit tomorrow!

[springcrocus]

Looking good.  Still following 
Regards, Steve

[Del_61]

Hi, your triple is looking great!!

One question how did you set the crank big end offsets?....presumably they are at 120 degrees, so I am interested in how you set this up.

What grade of loctite are you using? Are you going to reskim  after loctiting ?

Sorry for all the questions  !

Kind regards

Derek

[simplyloco]

SNIP
Sorry for all the questions  !

Kind regards

Derek

Hi Derek. Bear with me, all your questions will be answered by my next post.
John