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Northumbrian Cylinder Ports

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Doubletop08/11/2011 07:22:15
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Can anybody help decode this part of the instructions please regarding the drilling of the passage from the exhaust port to the exhaust passages
 
"Now consider the angle necessary for drilling through the floor of the exhaust port to meet up with these two holes. The starting point for drill will be about 1/16" from the bolting face, and the port face will be roughly 10deg. from the vertical.".......
Start with say a 1/8" drill, on the center line of the port........"
 
"drilling through the floor of the exhaust port to meet up with these two holes" so we start in the exhaust port.
 
The starting point for drill will be about 1/16" from the bolting face, Where on earth is this point? the closest edge floor of the exhaust port is 3/8" from the bolting face.
 
and the port face will be roughly 10deg. from the vertical."....... Start with say a 1/8" drill, on the center line of the port . A 1/8" drill at with the job 10deg from the vertical will rip into the outer edge of the port.
 
I've drawn it up and the shallowest angle looks to be around 25deg and eve that looks too shallow. I've sketched up this to demonstrate. the drill is at about 25deg


Any clues?
 
Pete
 

 
Alan Reed 108/11/2011 10:01:20
10 forum posts
I think you are possibly referencing the wrong face . The bolting face referred to could be the face for the cylinder cover . The ports being at each end of the cylinder block with a small flat as per the Stuart 10V.
Tel08/11/2011 10:01:30
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What's it for Pete? I would be inclined to deepen the exhaust port a bit more to help line things up and then go in from the screwed(?) hole in the bolting face.
Alan Reed 108/11/2011 11:21:44
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Pete, I think this will solve you problem
 
http://www.model-engineer.co.uk/forums/postings.asp?th=36393
 
Rgds
 
Alan
DMB08/11/2011 14:38:03
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I understood that the way to do this job is to file/mill a flat on the edge of the bore and drill "up" the slope in the direction of the bottom of the `trench` (port). LBSC and Martin Evans recommended this method and possibly, a good many more designers would have done likewise.
The cyl. block set up in a drill vice at an angle and `sighted`.
John
JasonB08/11/2011 16:38:08
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As its the exhaust port you won't be drilling from or to the bore!!
 
I'm with TEL either extend the hole from the side of teh block or deepen the port.
 
J
Doubletop08/11/2011 20:07:18
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Thanks for the replies everybody. This is for the "Northumbrian", silly me I posted it under the Northumbrain thread and then realised that information isn't carried through with the post. It was too last after I'd sent it and as far as I can see, unlike other forums there's no way to edit your post on this forum.
 
Its another area where the magaizine write up and drawings could have been better. Its taken a bit of interpretion to work out what was intended, reffering across a number of issues. This bit is just gobbledy gook, and you can imaging getting to this point on the cylinders theres a reluctance to stuff it up.
 
Pete
JasonB08/11/2011 20:34:27
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A quick look at teh Northumbrian drawings and the 10degree angle in the text is wrong, you only have to look at it to see its far steeper than that, more like what you have shown. I see it also says about deepening the port as Me and Tel suggested.
 
It also says 7/16" from the bolting face NOT 1/16" and thats not far off your  3/8"
 
J

 

Edited By JasonB on 08/11/2011 20:40:40

Doubletop09/11/2011 03:37:50
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Thanks Jason I thought you may come up with the answer. My copy of this article is a bit poor as a result of the on-off availabity of pdf copies of the online versions of the magazine on MHS.
 
I'm going to use about 27deg and predrill with a 1/8" end mill to get face to work off, centre drill and then drill 2mm and then try to go up to 3.2mm
Doubletop09/11/2011 07:51:02
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Well got home from work tonight and took the view stop messing and get on with it. So set the block at 27deg as planned and started on the exhaust port with a 1/8" slot drill. [Not end mill; I keep mixing up the terms because with a slot drill you use the end and with an end mill you use the side (more or less) .]
 
Anyway rather than then move to a drill I continued the hole with the slot drill as its stiffer and was going where I wanted it to. With a bit of fiddling about I got the exhaust port holes joined up.
 
I then moved to the inlet, rather than try and get the angles lined up for each port I did 2 x 3/32" holes 5/8" deep and .07" either side of the center line and 0.13" down from the port face parallel to the cylinder. They just come out into the bottom of the inlet port and I'll make the ports deeper to the bottom of the drill holes. On the cylinder ends I mill a 1/32" deep relief into the cylinder.
 
A few hold you breath moments just in case I'd missed something, but it came out fine.
 
Onwards and upwards.
 
Pete
JasonB09/11/2011 07:59:59
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Just make sure the 1/32" relief does not get blocked by the spigots on the cylinder covers.
 
J
Doubletop09/11/2011 08:06:34
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Jason
 
That did cross my mind, but you get the general idea.
 
I must do some more pics for the HMEM post, Things have moved on a bit since the last batch
 
Pete
Tel09/11/2011 10:00:05
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.
.. or nibble a little off the spigots in the appropriate place
 

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