Suffolk Four-Stroke

Over the holidays I have been working on a lump of aluminium to make a combined cylinder/crankcase for a model of my salvaged Suffolk lawnmower engine.

I'm no Brian Perkins, and to be honest its more a learning process than a medal winner! There are some serious mistakes, but none fatal so far.

Pics of the original and the (still very incomplete) block to compare:

Neil

What scale is it Neil?

Roughly 1/3 full size, so the block is just over 2 1/2" high.

Neil

Ahhh, ideal for those secluded window boxes ))

That's a nice piece of sculpting Neil - very compact - whats the capacity BTW and does the lawn mower come after

Nice to see something a little different again which reminds me whats happening to this project . Any further progress? I'd certainly like to know a little more

I see the ads over the text is back again - this is so bloody irritating - you don't get this on Model Engine Maker or HMEM (wink bloody wink)

Despite that a Happy New Year to you Neil - keep up the fine work

Regards - Ramon

It's looking great Neil. Are you planning to use a cast iron or steel sleeve in the block?

Or is your block made of high silicon aluminum like the original, to handle the rings running directly on the bore?

Briggs and Stratton in the USA pioneered the use of the hi Si alloy. It seems a bad idea on first glance, but I have seen many B&S engines 40-50 years old made this way and still running.

JD

It will be 3/4" bore, probably the same stroke so about 2.7cc.

I will use a liner - CI or steel with a CI piston. My original is the early 78cc small bore version with a CI block.

Hopefully today I will be able to finish profiling the crankcase part.

Neil

Hi Ramon,

Your link appears to be to the start of this thread - which project did you mean?

Neil

A little bit more progresh- HIC! Sory chilean wine is beginning to take its New Year toll... a drop of Pinochet Noir

I need some sort of cheer - the computer took about 12 restrats before I could post this

Neil

Looks great so far Neil.

Happy New Year to all.

JD

Hi Neil - It was your 'Ancient Engine' thread - I found that a very interesting and quite unusual subject.

I've spent the evening drawing out a new IC project 'running in' the new 'computer only' glasses - I'm hoping they will help cure this neck problem caused by using bi focals.

All the very best for the New Year and to all 'our friends' on here - I'm off now to see it in with a drop or two of malt

Regards - Ramon

Thanks Ramon,

The ancient engine is making me guilty as I embark on this one... although I have done some really nice work on the eccentric straps and rods (if I say so myself). Thinning them down from 1/8" thick was a challenge until I realised I could use the very tip of a huge clamp to hold them on the mill table.

This engine has been planned for ages and I set the target or making the crankcase over the break. It still needs a littl;e more shaping - reducing fin ends, the hole between the manifold attachments, some fixing holes and tapping.

I slightly bent the base with over-enthusiastic clamping. I spent ages rocking it on the 'surface plate' and tweaking it without success. Eventually I applied some engineer's blue that showed two small high spots. Rubbed off with emery cloth and solved in a minute!

I have no idea if this will work, but I plan to make the flywheel of solid steel (as there is no need for a magneto recess as I will use a glow plug and 'simple' r/c style carb). I will also make the 'fan-fins' shallower to get the maximum metal in the body of the flywheel. I can also add a slightly over-size 'pulley' on the far side and use a disc or balanced crankshaft, all to max the rotating weight.

Can you suggest what sort of compression ratio to aim for -about 8:1?

Also would you go for a well-lapped CI piston or use rings on such a small engine, given I have no previous experience of making either?

Final question - space is very limited inside the crankcase so I thought of a solid big-end and a two piece crank with a small pin inside a big one (I've seen this done using a taper) The crank will be well supported with long bronze bushes either side.

Neil

Some more progress. Many thanks to Rod for advice on springs.

Neil

Quite a lot of progress now, last big job is to make a carburettor!

Neil

Edited By Stub Mandrel on 11/05/2013 16:23:43

Hi Gray,

I HOPE it looks like the ones fitted to Qualcast mowers!

My regret is not making it 1/2 size instead of 1/3, not much more work, but a lot less fiddly.

I might write it up - if it works!

Neil

Edited By Stub Mandrel on 11/05/2013 19:23:38