Early days on the Hemingway kits Major Seal 30cc designed by Edgar Westbury. I've been involved in many machining projects over the years and have a background also in boat building but this is my first time building an entire engine from pretty much scratch. Being mostly self taught this might not be a totally conventional way of building. I'll be learning along the way! Super glue jiggings parts together? I must say it worked out well though! Onwards and upwards!
Major Seal 30cc Build
- Thread starter Basil
- Start date
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Back on the Seal Major build now I'm finished with the tool post grinder. I have the liners pretty much done just honing to final size. Piston clearance is not mentioned in the plans. Advice would be much appreciated on this. The bore size is 13/16". Cast Iron liners with pistons machined out of aluminum (Dural) bar stock. On the racing Zenoah's (bigger piston at 34mm) they run 1 to 2 thou." diameter reduction above the ring in the combustion zone.
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Finally done with the crankshaft after I don't know how many hours! Happy with the result though and that's the main thing. Learnt lots along the way also.
Now to the other 3 pistons now I've got that procedure understood.
Now to the other 3 pistons now I've got that procedure understood.
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I'd be lost without superglue to match drill etc. Harbor Freight works just fine. Consider some instant set spray and release.
Moving onto the cam! The firing order on the plans is 1243. This is an unusual firing order for a 4 cylinder engine, most everything I've seen is 1342. As I've mentioned before this is going to be installed in a boat and I have decide to have the flywheel at the front which will have a gear and one way bearing for an electric start. All of this messes with the cam lobe positioning not to mention the 1 exhaust, 2 intakes, 1 exhaust and a repeat of the same for port configuration.
To clear this up in my head I decided to CAD it up. I have been 3D printing for about a year now with an Epax X1. CAD is a fantastic tool but I find there is no substitute for holding something in your hand and giving it a good lookover. I machined a flywheel up for another boat a while ago, drew something up in CAD and thought "that should do it". Decided first to 3D print before cutting metal. When in hand it was obvious it was too small for the engine.
Very happy to have something to refer to when getting ready to grind the next set of lobes. I absolutely detest throwing parts in the bin
Some pictures of my 3D resin printing.
Onwards and upwards!
To clear this up in my head I decided to CAD it up. I have been 3D printing for about a year now with an Epax X1. CAD is a fantastic tool but I find there is no substitute for holding something in your hand and giving it a good lookover. I machined a flywheel up for another boat a while ago, drew something up in CAD and thought "that should do it". Decided first to 3D print before cutting metal. When in hand it was obvious it was too small for the engine.
Very happy to have something to refer to when getting ready to grind the next set of lobes. I absolutely detest throwing parts in the bin
Some pictures of my 3D resin printing.
Onwards and upwards!
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Back to the drawing board on the cam. As a few have noted the lifter face on the Seal Major engine is not really large enough to be ideal. If I incorporate a mushroom head on the lifter, material would need to be machined away at the bottom portion of the lifter bores which would leave them quite short. It looks like changing the base circle is the best way to go. Is there a reason why I shouldn't do this? Thanks
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Eccentric
Active Member
This is a copy of another Westbury sleeve. It is interesting that he calls for a .001" interference fit to the block both at the top of the sleeve and the bottom, but the lower hole in the block is .010" smaller diameter. For ease of installation I guess.
This is also from Westbury: Aluminium alloy pistons should have about 3 thou clearance at the skirt, increasing above the gudgeon pin by tapering, or easy steps, to 6 thou. The inside of the skirt should be machined as far as the gudgeon pin bosses will allow.
I simply use .005" clearance between the piston and sleeve.
Eccentric
Active Member
Your crankshaft looks great. How do you insure the tool post grinding wheel is perfectly flat and perfectly aligned side to side?
Steamchick
Well-Known Member
Curious comment about top and bottom fits of the cylinder liner being different... But when running, the temperature is different. So the sizes are probably optimised by Westbury based on his calculations for fit - and finished size when at running temperature.
Similarly Pistons: As the crown gets "flippin hot" with combustion heat and expands much more than below the ring pack, it is NORMAL PRACTICE in production engines (like your car) to have appropriate clearance WHEN at its HOTTEST, so the piston does not touch the bore above the top ring, or between rings: Only below the bottom ring (about where the gudgeon pin bosses start) do you get the size for the sliding fit of piston to bore: The skirt does ALL the alignment of the piston - even though in the latest car engines it is more of a "jock-flap" than a skirt!
Just my guesswork... but may be of interest?
Cheers!
K2
Thank you. I put a faceplate on the spindle and used a parallel against the grinding wheel as a start then put a dressing stone fixture in the spindle and dressed the wheel as needed. Every time the grinder gets installed the wheel will need dressing to get the best results.
Steamchick
Well-Known Member
Hi, just spotted this. Remembering the dedicated crankshaft grinder when I was a lad (part-time apprentice?)... the weekly maintenance included adjusting "the slides and gibs". Actually, there were nor slides and gibs as the stone was on a set of lever mounts on bearings, but the dial knobviously that turned the thread to introduce the stone to the wheel needed the covers removing and cleaning, to try and reduce the wear of the fine thread and split nut. It was calibrated in half-thou as Oi recall, so a very fine thread to introduce the "cut".
I assume in this explanation the grindstone is set in place of the toolpost so the slack must be removed from the cross slide nut, and gibs set as close and even as possible without binding. Also the main carraige saddle gibs should be serviced, and lubricated. Do cover all surfaces with cling film, paper and masking tape etc. To keep the grinding dust from wearing out all the slide, etc. Use dust extraction, unless you are using a wet system (the dedicated crank grinder I used was oil cooled at the stone which was about 18 inches diameter!). You must use a tailstock centre to support the shaft, and the parallel journals were achieved as a combination of careful stone dressing before the "cut" and the traverse along the length of the journal. The corners of the stone had a radius to minimise stress ring at the ends of the ground surface of the journal, so journals on your crank should ensure adequate length for the radiused corners the stone will give you, beyond the journal bearing surface.
Enjoy!
K2
I assume in this explanation the grindstone is set in place of the toolpost so the slack must be removed from the cross slide nut, and gibs set as close and even as possible without binding. Also the main carraige saddle gibs should be serviced, and lubricated. Do cover all surfaces with cling film, paper and masking tape etc. To keep the grinding dust from wearing out all the slide, etc. Use dust extraction, unless you are using a wet system (the dedicated crank grinder I used was oil cooled at the stone which was about 18 inches diameter!). You must use a tailstock centre to support the shaft, and the parallel journals were achieved as a combination of careful stone dressing before the "cut" and the traverse along the length of the journal. The corners of the stone had a radius to minimise stress ring at the ends of the ground surface of the journal, so journals on your crank should ensure adequate length for the radiused corners the stone will give you, beyond the journal bearing surface.
Enjoy!
K2
I've brought the base circle down to 3/8"to allow clearance for the enlarged lifter head which will be 1/16"thick on the face. The flank radius is 3/4" with a nose radius of 0.0625 on the exhaust and 0.0235 on the intake. Crank duration is 228 intake and 234 exhaust which I feel is a little on the low side. Might work on this further. I have a OS 30 I will use for comparison. Fusion 360 is amazing for mocking up these assemblies.
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