A strange Stuart MTB1

[redhouseluv]

That's me trying to spin the flywheel out of shot rather than the engine I think - I was surprised to see how much those Saito engines cost, a pretty penny!

[crueby]

Many decades ago I got one of those Saito V-4 engines as part of a steam launch kit, from the company Laughing Whale I think. Very neat little engines, run quite well, and the self start makes it perfect for marine use. You are right, the prices on them these days is eye watering! Keeping mine!

[redhouseluv]

Deep joy! 

After a good soaking in Liquid Wrench and some focussed & controlled violence both the flywheel and more importantly the cam are off and nothing is damaged.

Next is to clean up the cam and drill/tap a locking screw and see if I can reuse the flywheel, if not, I have one that needs machining

[crueby]

...some focussed & controlled violence...

I like that phrase!

[redhouseluv]

Even though I can now vary the timing via the cam, I'm 5 hours in to trying to get this to run!!!

1. The distance the cam is along the shaft effects:
- how even the ports open either end of the stroke
- the timing
- the gap between the lever arm and the cam

2. The tension of the spring also impacts if the lever arm is in constant contact with the cam

3. The threaded end of the valve rod which sits in the fork end of the lever arm also impacts how even the ports open either end of the stroke

4. There is lateral movement in the crankshaft (see video) which shifts dependent on whether the spring is under tension or not. I think a bush between the cam and casing will remove this

https://youtube.com/shorts/kV_QnPcSvc0?feature=share\

5. Nearly, forgot ...... the flywheel end of the crankshaft is bent, I thought it was ok, but sadly not

I haven't yet consigned the engine to the 'novel paperweight' category yet (getting close), but can clearly see why Stuart's gave up on this mechanism very quickly and moved onto the bevel gears. There are way too many variables to set and they all effect each other, so by setting one thing you change another! 

[redhouseluv]

I was wondering why the valve rod was getting stuck at the end of its stroke and look what just fell out of the valve chest! I take my hat off to whoever made it, it's teeny! I guess they messed up the hole and tried to plug it.

I'm going to do the same, but I'll try some good ole JB Weld and then drill it

[redhouseluv]

Ok, I'm beaten 

Nothing I've tried can get this engine to run; even making the new hole for the valve rod for in the valve chest didn't help. I've set the timing correctly, the port just starts to open at TDC marked by the black line on the flywheel. (see video)

https://youtube.com/shorts/WQs1UeDyFgE?feature=share

I can't think of anything else which can be done, if the timing's right, it must be something with the cam. lever, spring combination which must be causing the issue

I guess there was something wrong with this little engine before I got it as someone in the dim and distant past made the modifications and the fact Stuart's abandoned the design .........oh well, consigned to the 'novel paperweight' shelf after all .......grrrrrr 

[crueby]

What happens when you try to run it? Air blowing through at times, any force on the pistons? Partial movement then stop?

[redhouseluv]

The engine rotates, but not without some manual spinning of the flywheel, then partial and stop ........

[Dave Otto]

Shouldn't the port start to open after TDC and not before?

Dave

[crueby]

Looking back at the pictures, where is the exhaust going? I don't  see an opening for it other than the vertical hole between the  cylinders when the head is off. Assuming there is a port somewhere, is air coming out when pressure is applied through the top inlet but before rotating the wheel? And while rotating is it a constant flow or the occasional  puff? And how much pressure are you giving it? This type would need a high pressure and flow, more than a small wobbler.

[crueby]

Shouldn't the port start to open after TDC and not before?

Dave

At least at or after, before only with a high speed run.

[redhouseluv]

Here's a video of what happens when I try and run the engine and the photo below is of the exhaust port (and smaller crankcase port). I have the air pressure cranked right up.

https://youtube.com/shorts/8IqLUVNuq4w

Interestingly I checked where the air tries to escape from before rotation and its either via the exhaust port OR the smaller hole in the crankcase! Doesn't this suggest that the rings are shot and air is getting past the pistons into the crankcase?

[crueby]

The initial air leak is likely the  valve not sealing against the port face at first, then when you rotate its snapping down and sealing. Not uncommon in steam engines.


It does look like the air is blowing by the valve at either end of its travel. Two possibilities.  1, the adjusting nut is too snug and its lifting the valve, you want the valve to be able to slightly  wiggle up and down on the nut throughout the  travel. If the rod is lifting as it moves, that could also lift the valve if the nut is too snug.  2, the valve may be too short and air is getting past both ends when it is centered. Okay, three possibilities...  3, if the center cavity is too long, air can go under the end as it opens, across the port, and into the cavity and blow out the exhaust.


It looks like there is enough seal on the pistons,  a little blow by is okay. To check that, lower the pressure  a bit if need be so you can hold the flywheel at midstroke. If the seal is bad you'll get  a lot of air out the crankcase.


Hope that helps!

[redhouseluv]

Thanks for the diagnosis Chris, a few things to think about, mainly around the valve

1. The valve and nut are a little on the tight side so I'll free them up some more and make sure there's some wiggle
2. Can I visually check this? What should I see with the valve centered, both inlet ports covered?
3. What should be the correct cavity length in relation to port width? Is there a way of measuring calculating?