Attkinson engine & the Pendergrast design..

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DKGrimm

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Gordon, I see that you're right; the Colorado club site no longer has the article I followed. And it's absolutely true for this AD engine that ring seating is critical. I did find a copy of that procedure. My copy was made in 2007, but I've seen an earlier copy from as far back as 2003. I'll attach the here, assuming ownership and copyrights and all that stuff is not an issue.
 

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dsage

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OK.
Here is a link to the files I created:


It seems Greg might have run into some trouble trying to arrange the files to be shared. I've contacted him & he did truly want to post them. I've put them here on my drive to be shared. I may receive some "Flak" for sharing them, but it seems Greg was granted "Permission" from the original designer, A. Brooks Pendergrast, so I'm putting them up. If there are any issues involved in doing this, I will take them down immediately.

A lot of time was spent in doing these drawings, & I made every effort to preserve the original design intent. I recreated the CAD models from the original hand sketched drawings. The only "Liberty" I took with them was in changing some of the dimensions to more of a "standard" layout, (Some parts were dimensioned from both sides of the parts, some had some missing dimensions...) I recreated the build notes as well from his hand typed documents (I HATE typing), so there could very be well errors, I made no attempt at fixing spelling & grammatical errors. I did decide not to use all cap's though...what you have is exactly what he provided in his original info.

There is a small BOM included with the build notes & I have included what I feel to be a more complete BOM. The file name is "MBM.PDF" & it lists all the parts & what drawing they can be found on.

Lastly, all credit goes to A. Brooks Pendergrast for the design & thanks to him for agreeing to share his design. Thanks to Greg for giving me the opportunity in recreating the drawings. Standard disclaimers apply, use at your own risk & no claims are made that this design is a successful one.

John
John:
As I always do I redraw all drawings that I receive.
I might have missed something but it appears you have left out ONE of the most important dimensions in the drawings - the location of the spark plug hole.
Please elaborate.

Thanks
 
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johnmcc69

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Dave, see drawing #5, sheet-2, front view. The location is shown as .31 ("X") & on cylinder CL.

The hole SIZE, which is not shown, is M10x1. (to elaborate...) ;)

John
 

dsage

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Sorry. I didn't notice that pdf had two pages. Changes made.
Thanks

Now for another related question.
I did an animation of the engines motion works and I have doubled check all the dimensions that I think affect it.
It appears that the right hand piston almost travels past the spark plug hole. There's just a small opening left. The left piston is fully past the hole plus a bit to the left.
Have you ever observed this? I was expecting both piston tops to stop right in front of the hole.
 

dsage

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Here is what I get from my animation. I will add that the pistons tops are both nicely in front of the exhaust hole when they travel to the right so I don't think the cylinder is misplaced. Again, I'm just trying to be sure I have everything in order and would appreciate feedback on what you observe in your model (or on your engine if you have made one).
Thanks


Pistons location with respect to SPARK PLUG hole:

1616414051259.jpeg



Piston location with respect to EXHAUST hole:

1616414302374.png
 
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Gordon

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Here is what I get from my animation. I will add that the pistons tops are both nicely in front of the exhaust hole when they travel to the right so I don't think the cylinder is misplaced. Again, I'm just trying to be sure I have everything in order and would appreciate feedback on what you observe in your model (or on your engine if you have made one).
Thanks


Pistons location with respect to SPARK PLUG hole:

View attachment 123927


Piston location with respect to EXHAUST hole:

View attachment 123928
Perhaps the timing is intended to be slightly past TDC so that the RH piston has cleared the hole and the LH piston has not yet covered the hole. Moving the hole would make firing at TDC mandatory. Just a thought.
 

dsage

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Thanks Gordon. I posted the same question to gg... who just completed his on the Atkinson thread and has it running. He showed some nice pictures of the pistons about as I came up with. Apparently a 6mm drill fits in through the 10mm sparkplug hole over top of the piston.
So for whatever reason mechanically it seems to be correct.

You could be right. Maybe firing after TDC slightly will allow the RH piston to be on it's way down. Maybe with the wacky mechanism it can't tolerate having to fight the combustion early as is normally the case.
Something to keep in mind. Good thinking.

I'll consider my RE-drawings correct and continue on. I hate to start over on this engine but I'd still like to have one of these so I'm considering it. Probably a next winter project.
Thanks
 

johnmcc69

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Dave, I checked my CAD model & it is exactly how you have it with the piston partially blocking the spark plug hole.

John
 

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