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Whittle V8 Camshaft and Conrod Collision.

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Pete Savage26/09/2018 20:48:36
15 forum posts
6 photos

Hi Guys,

While sorting out my lathe I decided to draft the engine up in cad. I have assembled everything and turned it over, only to notice the conrod collides with the lobe on the camshaft.

I make the distance between crank and camshaft 0.5625in, which as far as I can tell is correct, so I am calling on anyone else who has made this engine to tell me where I have screwed up?!

Cheers,,

Pete

JasonB26/09/2018 20:56:57
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13462 forum posts
1229 photos

He gives 0.5625" in the ME article and that also agrees with the gear PCDs

Just a thought but do you have the camshaft rotating when you turn the engine over in CAD as it may be they don't clash when timed correctly

Edited By JasonB on 26/09/2018 20:58:24

Emgee26/09/2018 20:58:57
872 forum posts
182 photos

Hi Pete

I am in the process of building the same engine, work to date includes all ally bits and the camshaft,
now on the 4th attempt at the crankshaft !!!!

Are you certain the camshaft is built to the drawings, that is are all cams aligned as per drawing and timed for correct opening periods. ?

Emgee

Emgee26/09/2018 21:36:51
872 forum posts
182 photos
Posted by Emgee on 26/09/2018 20:58:57:

Hi Pete

I am in the process of building the same engine, work to date includes all ally bits and the camshaft,
now on the 4th attempt at the crankshaft !!!!

Are you certain the camshaft is built to the drawings, that is are all cams aligned as per drawing and timed for correct opening periods. ?

Emgee

milled camshaft.jpg

Pete Savage26/09/2018 22:08:49
15 forum posts
6 photos
I timed it with cylinder 1 at TDC and the cams in the overlap point like the article says.
Pete Savage26/09/2018 22:27:46
15 forum posts
6 photos

1.jpg

Here only cylinder 2 is visible but cylinder 1 is at tdc where cams are in overlap area. When rotated around the edge of the conrod touches the cam lobe.

2.jpg

Edited By Pete Savage on 26/09/2018 22:34:28

Pete Savage26/09/2018 23:30:20
15 forum posts
6 photos
Posted by Emgee on 26/09/2018 20:58:57:

I am in the process of building the same engine, work to date includes all ally bits and the camshaft,

now on the 4th attempt at the crankshaft !!!!

When I get to building, I am going to try doing the crankshaft using a live centre at the right end, but gripping the other side in a 4 jaw chuck using a dial indicator on the tool post to get it parallel.

I hope this will give me a bit extra stiffness at the end, but I have ordered enough bar to make 3 as I have heard other people's problems!

JasonB27/09/2018 07:03:20
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13462 forum posts
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CAD is only as good as the info you put in, have another look at the original drawings.

v8 conrod.jpg

Edited By JasonB on 27/09/2018 07:03:51

Pete Savage27/09/2018 08:40:25
15 forum posts
6 photos
That's the ticket! Didn't notice that, I must have seen it at some point, but I go off and come back to this project quite a lot. Thanks for the help!
Pete Savage27/09/2018 11:43:00
15 forum posts
6 photos

Emgee, When you were machining your cam shaft, did you assume the radial pin point order was towards the outside of the jig or the inside? As I understand it at the moment, the end of the shaft with the 2 different diameter bits on the end is the rear/cyl 7&8 end, which goes through the clock dial and into the 245 slotted wheel.

I aligned the centre of the lobe to the opposite of this point for the corresponding cam position, assuming the points were on the outside, however the shaft appears to now be a mirror image of what it should be.

On an unrelated note, the purpose of the arbitrary "Index pin hole" seems like an added complexity, those holes could just be numbered with what cam number it was!

Emgee27/09/2018 15:01:10
872 forum posts
182 photos

Hi Pete

My setup for milling the cams, see note on picture ref ends.

v8 camshaft.jpg

Emgee28/09/2018 11:01:36
872 forum posts
182 photos

Pete

Is it possible to modify the rod drawing to allow for the clearance to the camshaft when modelled ? so providing dimensions of material removed for clearance.
Is fouling at the same part of the rod for all cylinders or is it variable ?

Huge benefit to those still to make those parts, save dismantling to file rods and assemble again.

Emgee

Pete Savage28/09/2018 15:20:21
15 forum posts
6 photos

I think a chamfer of 1.5-2mm on this edge is enough for clearance.

 

EDIT: It is on the opposite side to in the photo

1538143937266313442542.jpg

Edited By Pete Savage on 28/09/2018 15:31:44

Emgee29/09/2018 09:45:44
872 forum posts
182 photos

Pete, thanks for the info.

Emgee

John Roberts 1011/10/2018 18:04:37
5 forum posts
1 photos

Yes I can clarify that relief on one side if the con rods is necessary. I attach photo of the finished engine. For me the biggest challenge is getting the engine to run. I have now a power supply which gives correct power to glow plugs and tried a high nitro fuel, but there is air leakage though the valves despite grinding/lapping valves in. The next option is to try more powerful springs and possibly remaking pistons which are taller. The hope of raising compression. I am confident that I have timed correctly. Any one in the process of making this engine take an extra effort to prevent air escaping other wise you will be in the same boat as me.

My attention has now moved on to making the Blackmore Bentley BR2 Rotary engine. I would be very interested in contacting anyone that has made one as I have some questions!!

p1010751.jpg

Jeff Dayman11/10/2018 18:20:27
1267 forum posts
33 photos

Hi John, a few questions -

-what sort of head gaskets are you using? even though you may be hearing air leak past valves, often head gasket leakage can be an issue also. A light smear of silicone bathtub caulk on cyl head gaskets and on all intake manifold joints can help air sealing in small engines greatly.

-what sort of valve stem to valve guide clearance do you have? There needs to be some clearance, to permit the valve to "find" the seat. Some grease in the valve guides rather than oil can help seal the intake valve stems against vacuum leaks if no rubber stem seals are fitted (most small 4 stroke engines do not use rubber stem seals, not sure if the Chenery engines do or not.)

-have you "motored" the engine with a drill motor or other aux motor for several hours (or days) to break in the piston rings and establish a seal of piston rings to bores? "Motoring" while adding drops of oil down the open spark plug holes periodically may significantly raise the compression and improve sealing. Be sure to disconnect the ignition while motoring to prevent damage to ignition system.

Hope these ideas help get your engine going.

John Roberts 1011/10/2018 23:34:57
5 forum posts
1 photos

Jeff,

Thank you for your comments.

The head gasket is a thin copper ring between cylinder and head. I used copper grease to help seal. I did not check for leaks here as all cylinders were machined at the same setting so each bank of four should be on the same plane.

I will immerse the engine in white spirit to check for leaks here. then try adding silicone to joint faces as suggested .

I did run the engine first with it totally submerged in oil with lower crankcase removed and no plugs fitted at a few thousand RPM finishing at 5000 rpm using a prop starter with it fully assembled. Cylinder bores are polished from this process with most radial honing lines removed..

The valve stem to valve clearance could be increased and was something I intended to do as there is little axual play at present. I did not re ream valve guides after pressing in to head.

I found that if the crankcase had too much oil in there it would get past the each ring and fill up the glow plug with oil. For me I found the correct level was just enough for the crankshaft to dip into and through up the bores.

The valve seating were tested by immersing the heads in white spirit and blowing though a tube connected to each manifold in turn. Air bubbles were seen with little improvement after further lapping. This is why I intend trying stiffer valve springs.

I hope these observations might be of interest to other builders of this engine.

Pete Savage11/10/2018 23:41:47
15 forum posts
6 photos
I have the hemmingway kit, and did wonder whether the springs would be stiff enough, the four stroke RC engines I own have pretty stiff springs.

Maybe it would be possible to make a little valve seat cutting tool that locates into the valve guide to get higher precision.

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