Can someone please explain this angle?

[nigel jones 5Participant @nigeljones5]

This is the end view drawing for a Stuart No.9 crankshaft – nothing especially interesting about it but I am perplexed as to the way it has been drawn and cannot fathom what the 30 deg angle relates to?

[nigel jones 5Participant @nigeljones5]

[John HaineParticipant @johnhaine32865]

Isn't the dotted circle the profile of the eccentric?

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Fizzy, I would take it as being the angle of offset of the eccentric to the crank.

Regards Nick.

[nigel jones 5Participant @nigeljones5]

Thanks both, I thought about that but without other reference It just seems like a pointless angle as it doesnt depict the centre of the eccentric, just the centre of the crank? Still confused.

[JasonBModerator @jasonb]

The line passes through the maximum throw of teh eccentric so assuming the crank is rotating anti clockwise then the eccentric leads the crank by 90 deg plus 30deg of lead which is common on most Stuart engines. See the post the other day about timing an engine with reversing gear

Put simply the grub screw hole in the eccentric's boss should be at 2 o'clock when crank pin is at the bottom

 

Edited By JasonB on 25/02/2018 20:51:29

[HopperParticipant @hopper]

If you wanted to get really technical you could measure it exactly with a dial indicator on the eccentric to find the highest point and a degree wheel on the crankshaft to set the exact angle, bit like how we set racing cams in vintage Harley-Fergusson engines.

It might be hard to find the exact high point reading on a smooth curve like the eccentric so you would have to measure the points each side of it where you got a reading of minus 30 thou (say) and find the centre of those two points using the degree wheel.

Meh. Better to do like Jason says and set the screw hole at the stated place!

[Martin ConnellyParticipant @martinconnelly55370]

Fizzy, doesn't the drawing for the eccentric show the position of the shaft/hole? That and the indicated angle are all that is required for correct phasing.

Martin C

[JasonBModerator @jasonb]

This is Stuarts guide to setting the valve, your 30deg angle is what is talked about in the first paragraph and what I said above eg eccentrics max throw is 90 +30 ahead of the crank pin

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