Author Topic: Len Mason's "Mastiff" - chewed from the solid  (Read 27086 times)

Offline Roger B

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #210 on: October 03, 2018, 05:36:21 PM »
That's a good carburettor build  :praise2:  :praise2: I like the technique for the adjustment wheel  :ThumbsUp: The first start can require perseverance  ::)  ::)  :wine1: 
Best regards

Roger

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #211 on: October 09, 2018, 12:42:26 PM »
Thanks everyone for the comments. MJM - I'll be in touch soon.

The last week has seen a steady increase in the compression and the amount of firing (when spun over with a cordless drill) but still no independent running.
So far I have:

Re-checked the valve timing - only a small change there.

Adjusted the contact breaker cam position - this was too far advanced to allow setting the spark much after TDC. Checked this with a strobe timing light.

Adjusted the dwell and debounce settings in the electronic ignition - now 4 mS dwell and 1.8 mS debounce time. During this bit I managed to burn out a coil. This is a cheap coil-over-plug unit meant for a 6-cylinder Ford and the replacement seems to be running much cooler, the original timing had the dwell and debounce times much longer. Also, if the debounce time is less than 2 mS the firmware for the ignition turns the coil off after 1 S of no triggers, with longer debounce than that it leaves the coil active for 10 S, probably the little coil couldn't take that.

Cleaned a very small amount off the tops of the blocks in the mill and polished them flat on the surface plate:



I'm not sure this was necessary but at least joint leaks can't be reducing the compression any more and the gaskets should last longer.

Spent a long time at the stereo microscope picking tiny bits of metal out of the valve seats with a bit of copper wire (sorry, I don't have a camera adaptor for this so no pictures). I don't think I'll use Al alloy valve seats again...

Fiddled endlessly with carby settings, definitely vital but still no more than a few consecutive bangs. Whilst doing this last night I put a hand in the right place for the first time and felt pulses of gas coming from somewhere where I didn't expect it, somewhere near one of the spark plugs. At first I thought the plug wasn't tight, not so. So the sealing ring (or seating) isn't flat? also not the case. Made new alloy sealing rings, no change???? It was definitely time to stop guessing and start thinking. Today I took off one of the heads and made up a blanking plate to close off one combustion chamber. This was drilled so that compressed air could be fed in using an air-brush line and the air brought in via a tiny adaptor originally made to fit the blow-down bush on my "Minnie" traction engine. {Airbrush fittings are M5 x 0.45 if you needed to know}:





Now I could try out plugs and sealing washers with a lot more control over things and the answer came very, very soon after turning on the air. If you look back through the build log you'll see that I made my own spark plugs from Hemingway kits and this involves gluing the bits together with JB Weld. Well I'm guessing that I made the gaps too small for this to be effective everywhere and there are leaks through the plugs. Clearly these have to be dealt with before going any further. Either try to destroy the JB Weld with heat, dismantle the plugs, and try again or take the easy but expensive way out and buy 4 Rimfire plugs (apart from Chinese copies these look to be the only 1/4 x 32 UNEF plugs available commercially?).

It's time to sleep on this one!

DT


Thoughts

Offline Craig DeShong

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #212 on: October 10, 2018, 03:55:29 PM »
Divide and conquer.   I'd go with the,store bought plugs, oncev it's running you can return to the home made.
Craig

Offline Brian Rupnow

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #213 on: October 10, 2018, 05:23:09 PM »
Deltango--This is an unusual thing that once happened too me. Are you turning the engine in the correct direction when you are trying to start it. Sounds like a dumb question, but if it can happen to me it can probably happen in Australia.---Brian

Offline Roger B

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #214 on: October 10, 2018, 05:40:02 PM »
These people also offer 1/4 - 32 plugs:

https://www.justengines.co.uk/acatalog/Ignition_Systems_for_Glow_Engines.html#aJW2015

I have used them on my vertical engine.

Otherwise go back to basics.

Do you have 'bouncy' compression on each cylinder (try one at a time with the plugs removed from the others).

Look at the valve timing. The inlet should open a little before TDC and close a little after BDC.  The exhaust should open a bit before BDC and close a little after TDC. There should be a noticeable overlap at non firing TDC. Check all cylinders just in case there has been a problem during the camshaft build.

Look at the spark for each cylinder after the above checks. Does each spark around the firing TDC for every cylinder (lay the plugs on top of the block).

Is there a strange advance curve in your ignition? The RCexcel unit I used retarded suddenly around cranking speed.
Best regards

Roger

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #215 on: October 11, 2018, 06:38:50 AM »
OK, commercial plugs are on order - thanks Craig for confirming what I thought was the right way to go.

Brian, I had this thought as well and (it isn't a dumb question at all) checked and checked again, I'm turning the engine clockwise (seen from the timing case end) and the contact breaker cam is turning CCW (seen from above), just as the designer intended.

Roger, there isn't much "bounce" from the cylinders, nothing at all like a model aircraft engine, but then the compression ration is only about 3.86:1 (per cylinder swept volume is 6.336 cc and combustion chamber volume is 2.211 cc from my Alibre models), 3.74:1 if you allow for a 0.4 mm gasket (I wonder if 0.4 Klingersil is too thick?).

The valve timings are "something like" you describe but I'll measure these again, an error in building up the camshaft is well up the list of possibilities.

I don't know the advance curve for the ignition, in fact I can't find any reference to it, I'll keep digging for that. It may be that there isn't one, it's a very basic unit.

I spun the engine with the plugs out and they sparked in the correct firing order - 1,2,4,3. With the plugs back in and a strobe light connected and triggered from each plug lead in turn the sparks were all occurring at very similar times just after TDC (thinking about it now, this may not guarantee that it was the firing TDC, um...). BTW, in the Mastiff book Len Mason argues that, in a side valve engine, valve overlap doesn't achieve much but he still designs it in.

I'm going to make up a 1/4x32 adaptor for the air-line so I can pressurise each combustion chamber in turn and check if the valves are seating. Poor compression is still at the top of my list with incorrect valve events second.

Many thanks for all the suggestions, I'll report back when I have more info.

Regards, David

Offline Admiral_dk

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #216 on: October 11, 2018, 11:31:17 AM »
Quote
the sparks were all occurring at very similar times just after TDC (thinking about it now, this may not guarantee that it was the firing TDC, um...)

This is too late - sparks need to ignite the fuel before TDC  :zap:
The reason : you should have maximum combustion pressure around 4 degrees after TDC, and it takes several mili-seconds for the fuel to burn completely => ignite before TDC. Usually only IC engines of several liters of cylinder volume might be able to run, if ignited after TDC and they will not be able to do work in this scenario.

Since you have such a low compression, I will also guess that you need extremely low friction for the engine to be able to idle well - but here I'm not sure  :thinking:

Best wishes

Per

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #217 on: October 11, 2018, 12:07:06 PM »
Thanks Per, I had my thinking wrong there. When I get some new plugs I'll re-set the timing to where you suggest.

I've now made the 1/4x32 air-line adaptor and pressurised each cylinder in turn. Numbers 1 and 2 are good, no leaks that I can find; #3 exhaust valve needs attention for a slight leak. Number 4 cylinder however has a significant leak to the water space but the gasket looks intact. Tomorrows first job is to find that leak path, hope it isn't a cracked liner!

David

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #218 on: October 26, 2018, 06:51:35 AM »
Mastiff is now running! My sincere thanks to all those who helped with advice.

I've just set up in YouTube and uploaded my first video, not a good experience but its done now:

The leaks to the water space were small (tiny) tracks around the tops of the cylinder liners where the JB-Weld hadn't quite filled the space when I assembled the liners to the block.

The plugs are Rimfire VR2L (good service from Morrison & Marvin Engine Works) and I adjusted the ignition timing slightly.

The valve timing is close to what is shown in the book but valve closing events happen a bit early - by an amount that could mostly be due to tappet clearances.

The compression is improving with running and all cylinders are starting to give a good "bounce".

I've re-made the carburetor needle with a shallower taper which has help with control but the engine is still running very rich and sometimes cuts out for no apparent reason. I'll keep working on the carburetor settings as the slow-running screw hasn't shown any sign of having any effect at all.

It's about time for a complete tear-down, clean, and re-build and then the "Mastiff" build story will be complete.

I'm feeling the need to start machining again so its time to dig out the "Wyvern" castings and build an IC engine the traditional way. There is also a big box of Southworth/Throp Corliss castings sitting with friends near Huntingdon and waiting for me to get over there and pick them up but they have to wait until next year.

Many thanks again to all MEM members who have helped and encouraged me along the way.

Regards, David

Offline Ye-Ole Steam Dude

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #219 on: October 26, 2018, 07:50:16 AM »
Hello David,

I absolutely love that little engine, and the wonderful sound. Wish your video was a bit longer. Great job  :ThumbsUp:

Have a great day,
Thomas

Offline Chipmaster

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #220 on: October 26, 2018, 08:11:50 AM »
Excellent, well done  :ThumbsUp:

Andy

Online Jo

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #221 on: October 26, 2018, 08:36:31 AM »
Well done David  8)

You have got me thinking about my set of Mastiff castings again  :thinking:

Jo
Usus est optimum magister

Offline deltatango

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #222 on: October 26, 2018, 09:01:48 AM »
Thanks Andy, Thomas and Jo,
I'll make a longer video the next time the engine is running.

For anyone who is an Alibre user (Jo?) I've attached the solid model of the whole engine (Alibre  .asm file; the Forum file size limit prevents me attaching the 3D .pdf).

Jo - I can recommend the engine as well worth the effort and the castings would speed thing up a bit. With your experience and "retired" status I doubt it would take you as long as it took me but it is still a lot of work. As far as I can see being "retired" only makes you wonder how you ever had time to go to work.

Regards, David

Edit 27 Oct 18: Removed the attached Alibre file. There is a link to one that should be usable in a later post. Sorry about the mess-up folks! DT
« Last Edit: October 27, 2018, 09:24:59 AM by deltatango »

Offline MJM460

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #223 on: October 26, 2018, 12:49:20 PM »
A great result for all your work, David.  Congratulations.  That first run is certainly a major milestone. 

With some luck, a little final tuning will complete it.

MJM460
The more I learn, the more I find that I still have to learn!

Offline ShopShoe

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Re: Len Mason's "Mastiff" - chewed from the solid
« Reply #224 on: October 26, 2018, 01:24:52 PM »
I've been watching and waiting. It's great to see that running.

I'm looking forward to the new video, whenever it comes. (I'm Patient.)

--Shopshoe