By continuing to use this site, you agree to our use of cookies. Find out more
Forum sponsored by:
Forum sponsored by Allendale Jan 24th

slow running engine

All Topics | Latest Posts

Search for:  in Thread Title in  
Dougie Swan15/09/2010 19:36:42
185 forum posts
40 photos
My latest project is a steam launch that I would like to convert to I/C power
The Westbury seagull is the prime candidate for the power source which brings me to my questions.
What is the slowest rpm of this engine, I would like to have an rpm of 600 or 700, is this possible?
Will a single or twin give me the slower rpm I'm after?
To simplify things I might make it glow ignition will this make a difference to the low end rpm's ?
Will a heavy flywheel help?
Any help will be greatly appreciated

Edited By Dougie Swan on 15/09/2010 19:55:04

Stub Mandrel15/09/2010 20:25:05
4307 forum posts
291 photos
1 articles
Hi Dougie,
Unlike a steam engine which has max torque at 0rpm (when full steam pressure can bear on the stationary pistons), an IC engine's torque curve rises from nothing up to an optimum speed, then declines as the inlet/exhaust act to choke the gas flow. If you run an IC engine too slow it will struggle and be prone to stalling under any increase in load.
As a twin has twice as many impulses per rev it should be possible to run slower an equivalent single. Even so, unlike a twin double-acting steam engine which will have four impulses per rev and no 'dead spots', a twin IC engine wll have only one impulse per rev and only for rather less than half the stroke. This is why a heavier flywheel is needed for IC engine, and it  will always help any engine with slow running to increase the size of teh flywheel - increasing the diameter helps more than increasing the mass, if you have space.
All in all 600 rpm sounds very slow for a small IC engine which will rpobably want to be reveing at a couple of thousand rpm, perhaps build it, see what is its 'happiest' speed and experiment with gearing it down?
Bogstandard16/09/2010 09:15:53
263 forum posts
What Neil has said all runs true, what might be you main concern is building the engine in the first place.
You really need to find someone who has built one of these engines, because some of the E.T. designs are so far out on plan dimensions and casting qualities they usually end up under the bench.
The last one I built was the 'Whippet' (and mine does run), using the old Woking castings. If you followed plan dimensions and casting markings you would end up with head bolts going into the cylinder, and that is just one example, there were many more plan errors. I had to get an ali welding friend to build the castings up in strategic places.
Hemingway, who took over the range from Woking 'redid' the castings for it, the Modelenginenews chappies attempted to build a couple, and it seems to have died a death. Search for Whippet on this page.
The Seal is another very good example, the castings were redone by Hemingway, and they are very different from the original casting shapes, but no effort was made to put right all the outstanding mistakes on the plans,, things like exhaust manifold studs cutting through head hold down bolts etc.
So as I said, find someone who has previous knowledge of using the plans and castings of this engine, only then, after it is proved to you to be fairly easily built, start to think about getting it to run like you want it to.
David Clark 116/09/2010 10:17:08
3357 forum posts
112 photos
10 articles
Hi There
There is an E. T. Westbury yahoo group.
They will probably have answers.
regards David
Ian S C16/09/2010 12:31:41
7468 forum posts
230 photos
I would tend to run the motor at reasonable revs, and use toothed belts for speed reduction, they are easy to get as replacements for belt-sanders etc, It would alow you to lower the prop shaft, and keep the sump out of the bilge.I think i'd be looking at a motor speed  of 1500-2000rpm. If the launch is an old type of design perhaps you need a single cylinder engine that goes putt putt putt thats what I remember as a young kid watching the fishing boats, they were 20-30ft clinker hulled boats with a canoe stern, and a single cylinder engine of between 10 & 30hp.  Ian S C
Dougie Swan16/09/2010 17:55:06
185 forum posts
40 photos
Thanks for the replies
As Ian puts it above, it's the putt putt putt exhaust beat that I'm after.
I have heard of the problems with the westbury designs and that is one of the reasons the set I have have lain under the bench for so long.
I think I will probably make one to my own design from bar stock, the appeal of glow ignition is that I can install a simple circuit to keep the plugs energised at low revs
The model is "wide awake" a clinker hull around 50 inches long and l was thinking of gearing down the output through a reversing gearbox, if the engine was a twin with the cranks 180 degrees apart would that help the slow running?
MichaelR16/09/2010 18:09:29
358 forum posts
66 photos
Dougie, After the engine flywheel the pitch and diameter of the propeller also has a effect on the engine RPM, and the speed of the boat through the water, a bit of trial and error in that department may be needed.
Stub Mandrel16/09/2010 21:36:53
4307 forum posts
291 photos
1 articles
My Dad passed me a biscuit tin of well-made parts that may (or may not) have been made by my uncle. I worked out they were many of the parts for a Seal. The crankshaft was corroded slightly, but I used the electrolytic method to retrieve it and the cylinder liners (which are unfinished). Most of the major parts (crankcase, sump, head, timing gear cover etc.) had been made from the solid, all done very well.
The piston rods all had bronze bushed big ends. After a deal of messing around and cleaning up I eventually fitted the rods to the crankshaft in the crankcase. Because the big ends weren't to spec, they fouled the insides of the crankcase - so that's why it was an abandoned project! I will return to this one day, and either remake the piston rods or undertake major surgery.
Thanks Bog's for the heads-up of not taking teh measurements on the ETW drawings literally, or I could end up as disillusioned as the original builder!

All Topics | Latest Posts

Please login to post a reply.

Magazine Locator

Want the latest issue of Model Engineer or Model Engineers' Workshop? Use our magazine locator links to find your nearest stockist!

Find Model Engineer & Model Engineers' Workshop

Latest Forum Posts
Support Our Partners
Allendale Electronics
Eccentric July 5 2018
Eccentric Engineering
Subscription Offer

Latest "For Sale" Ads
Latest "Wanted" Ads
Get In Touch!

Do you want to contact the Model Engineer and Model Engineers' Workshop team?

You can contact us by phone, mail or email about the magazines including becoming a contributor, submitting reader's letters or making queries about articles. You can also get in touch about this website, advertising or other general issues.

Click THIS LINK for full contact details.

For subscription issues please see THIS LINK.

Digital Back Issues

Social Media online

'Like' us on Facebook
Follow us on Facebook

Follow us on Twitter
 Twitter Logo

Pin us on Pinterest