Re: Meddling with a Wisp

Rebel Moby /
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For unshrouding the spark plug I wrote an article for this before, just as a preamble, the idea of unshrouding the spark plug is so it is not hiding in a well. With easier access for the spark to be exposed to the fresh air-fuel mixture it will ignite a more robust flame kernel. The pathway from the ceiling of the transfers to the plug center is also partially obstructed by the "bumps" that raised the compression ratio. A slight shave to these bumps will clear that passageway. You will need to tinker about with your squish band after unshrouding because you would want to restore the compression ratio. The 5cc volume works well with the stock bore, you will need to make adjustments for the overbore.

ARTICLE

Stock AV7-AV10 heads have two basic shapes: open chamber, which is hemispherical; and closed chamber which has a large protrusion on each side of the spark plugs.

The volume of these heads is approximately 5cc for the closed chamber and approximately 8cc for the open chamber.

Stock 5cc heads are slightly restrictive towards the flow of incoming charge from the transfers.

An easy fix is to remove some of the material shrouding the access to the spark plug.

Then restore the original volume of 5cc by shaving the head.

You would need a marker, some files, some alumimium oxide papers (220, 600 and 800 works well), kerosene and fine steel wool to finish to a good polished look.

Basically you need to shave down a strip from the bumps on either side of the combustion chamber.

The strip needs to be 3mm at the center of the strip and taper at both ends.

Then remove the extra material around the spark plug thread insert at the top of the chamber.

Using hand files and aluminium oxide papers this is a 20 minute job.

Use a permanent marker to draw on the head where you will be removing the material.

The material removed will be to leave a 45 degree ramp, which you would them blend into the surrounding material

so the roof of the combustion chamber is smooth.

Check that there is no lip at the front of the chamber, this lip should also be blended in so there is no pocket when the piston is at TDC.

Start with reworking the sides of the chamber.

UnShroud02.jpg

After the sides are roughed out then move to the periphery of the spark plug insert.

Reworking this area calls for blending out the ridge between the chamber and the insert.

Carefully pare it down for a smooth transition.

After roughing out the material smooth out the transitions with 220 paper, then 600 and finally 800.

Use the paper wetted with kerosene. Finally buff out the work with fine steel wool soaked in kerosene and wipe out with a rag so she shines.

UnShroud06.jpg

Next shave the head to restore the volume of material removed.

Use a syringe with some 2 stroke oil to measure the volume of the chamber.

Stock is approximately 5cc with the right sparkplug installed (Champion L86C or NGK B6HS or equivalent).

Note how much extra volume there is in the upper chamber.

If you are attempting to go for higher then stock compression ratio calculate the target volume you need before you start to mill.

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Subject Written By Posted
  Meddling with a WispTopic by: Tom Boyd Tom Boyd 07/27/20 04:01PM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 07/27/20 07:20PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 07/28/20 10:57AM
  Re: Meddling with a WispRe: P D P D 07/28/20 12:18PM
  Re: Meddling with a WispRe: Jeremy Homser Jeremy Homser 07/27/20 08:11PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 07/28/20 11:07AM
  Re: Meddling with a WispRe: Stephen Keller Stephen Keller 07/28/20 02:05PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 07/29/20 12:56AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 07/29/20 12:59AM
  Re: Meddling with a WispRe: P D P D 07/29/20 07:58AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/20/20 05:40AM
  Re: Meddling with a WispRe: EH 📣FCC of the QCB EH 📣FCC of the QCB 08/20/20 03:35PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/22/20 11:05AM
  Re: Meddling with a WispRe: Rebel Moby Rebel Moby 08/22/20 09:25PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/23/20 03:35PM
  Re: Meddling with a WispRe: Rebel Moby Rebel Moby 08/25/20 09:32AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/24/20 06:10PM
  Re: Meddling with a WispRe: Rebel Moby Rebel Moby 08/25/20 09:45AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/25/20 06:19PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/26/20 04:56PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/26/20 05:04PM
  Re: Meddling with a WispRe: discontinuuity _ discontinuuity _ 08/29/20 04:22AM
  Re: Meddling with a WispRe: James P James P 08/29/20 05:03AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/29/20 01:51PM
  Re: Meddling with a WispRe: discontinuuity _ discontinuuity _ 08/29/20 05:04PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/29/20 06:29PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 09/17/20 04:14PM
  Re: Meddling with a WispRe: Rebel Moby Rebel Moby 09/18/20 10:48AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 09/23/20 03:32PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 09/23/20 04:05PM
  Re: Meddling with a WispRe: Rebel Moby Rebel Moby 09/24/20 09:40AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 09/24/20 05:42PM
  Re: Meddling with a WispRe: P D P D 09/24/20 07:19PM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 09/28/20 08:44AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 09/29/20 02:54PM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 09/30/20 08:40AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 10/08/20 04:58PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 10/08/20 05:07PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 10/08/20 05:15PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 10/08/20 05:22PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 10/08/20 05:24PM
  Re: Meddling with a WispRe: Jeremy Homser Jeremy Homser 10/08/20 05:34PM
  Re: Meddling with a WispRe: P D P D 10/08/20 07:03PM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 10/09/20 11:07PM
  Re: Meddling with a WispRe: Graham Motzing Graham Motzing 10/10/20 10:12AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 10/10/20 04:37PM
  Re: Meddling with a WispRe: Rebel Moby Rebel Moby 10/12/20 01:33PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 10/12/20 05:58PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 10/17/20 10:40AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 10/27/20 03:17AM
  Re: Meddling with a WispRe: Rebel Moby Rebel Moby 10/29/20 10:48AM
  Re: Meddling with a WispRe: Rebel Moby Rebel Moby 10/29/20 10:49AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 09/26/20 04:53PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 09/26/20 04:58PM
  Re: Meddling with a WispRe: P D P D 09/26/20 07:02PM
  Re: Meddling with a WispRe: b to the eff b to the eff 10/29/20 11:44AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 11/01/20 03:06AM
  Re: Meddling with a WispRe: Brandon Weiss (Detective brandon to you) Brandon Weiss (Detective brandon to you) 11/01/20 01:11PM
  Re: Meddling with a WispRe: Graham Motzing Graham Motzing 11/01/20 01:30PM
  Re: Meddling with a WispRe: P D P D 11/01/20 01:51PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 11/02/20 03:45AM
  Re: Meddling with a WispRe: Mike Boyd Mike Boyd 11/01/20 11:41PM
  Re: Meddling with a WispRe: James P James P 11/02/20 06:02AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 11/02/20 12:30PM
  Re: Meddling with a WispRe: Aaron Blair Aaron Blair 11/02/20 06:36AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 03/13/21 12:15AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 03/13/21 12:20AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 03/13/21 12:27AM
  Re: Meddling with a WispRe: Ryan Graeme Ryan Graeme 03/13/21 03:45AM
  Re: Meddling with a WispRe: James P James P 03/13/21 03:13AM
  Re: Meddling with a WispRe: DAЯT _ DAЯT _ 03/13/21 01:35PM
  Re: Meddling with a WispRe: Graham Motzing Graham Motzing 03/13/21 06:04PM
  Re: Meddling with a WispRe: Ryan Graeme Ryan Graeme 03/14/21 04:24AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 03/15/21 06:08PM
  Re: Meddling with a WispRe: Ryan Graeme Ryan Graeme 03/16/21 02:30AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 03/17/21 12:40PM
  Re: Meddling with a WispRe: Graham Motzing Graham Motzing 03/17/21 04:30PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 03/17/21 05:56PM
  Re: Meddling with a WispRe: Dirty30 Dillon Dirty30 Dillon 03/17/21 06:13PM
  Re: Meddling with a WispRe: P D P D 03/17/21 06:53PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 03/18/21 10:03PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 04/06/21 06:39PM
  Re: Meddling with a WispRe: DAЯT _ DAЯT _ 04/08/21 03:47AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 04/08/21 02:42PM
  Re: Meddling with a WispRe: Ryan Graeme Ryan Graeme 04/08/21 03:42PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 04/09/21 03:39PM
  Re: Meddling with a WispRe: P D P D 04/09/21 05:19PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 04/09/21 10:23PM
  Re: Meddling with a WispRe: Totally normal JBOT Totally normal JBOT 04/09/21 11:55PM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 03/17/21 01:20PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 03/14/21 01:40AM
  Re: Meddling with a WispRe: Chris Squid Chris Squid 04/08/21 01:44PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 07/21/21 03:27PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 07/21/21 03:33PM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 07/22/21 10:37AM
  Re: Meddling with a WispRe: DAЯT _ DAЯT _ 07/21/21 03:40PM
  Re: Meddling with a WispRe: Born to be WillD Born to be WillD 07/22/21 01:47PM
  Re: Meddling with a WispRe: Mike Boyd Mike Boyd 07/22/21 02:59PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 07/30/21 04:55PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 07/30/21 05:01PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 07/30/21 05:05PM
  Re: Meddling with a WispRe: Mike Boyd Mike Boyd 07/30/21 05:43PM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 07/30/21 10:33PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/07/21 05:11PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/07/21 05:16PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/07/21 05:23PM
  Re: Meddling with a WispRe: Graham Motzing Graham Motzing 07/30/21 07:43PM
  Re: Meddling with a WispRe: James P James P 08/07/21 07:57PM
  Re: Meddling with a WispRe: Stephen Keller Stephen Keller 08/08/21 12:04AM
  Re: Meddling with a WispRe: P D P D 08/08/21 07:44AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/08/21 05:22PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/14/21 12:27PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/14/21 12:34PM
  Re: Meddling with a WispRe: Stephen Keller Stephen Keller 08/14/21 03:51PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/14/21 04:07PM
  Re: Meddling with a WispRe: Mike Boyd Mike Boyd 08/14/21 03:26PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/14/21 03:53PM
  Re: Meddling with a WispRe: Stephen Keller Stephen Keller 08/14/21 04:43PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/15/21 03:31AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/19/21 03:55PM
  Re: Meddling with a WispRe: pat splat pat splat 08/19/21 11:32PM
  Re: Meddling with a WispRe: Stephen Keller Stephen Keller 08/20/21 03:14AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/20/21 04:53PM
  Re: Meddling with a WispRe: Mike Boyd Mike Boyd 08/20/21 06:03PM
  Re: Meddling with a WispRe: Aaron Blair Aaron Blair 08/21/21 04:37AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 08/21/21 06:22PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 09/05/21 05:35PM
  Re: Meddling with a WispRe: P D P D 09/06/21 09:48AM
  Re: Meddling with a WispRe: Mike Boyd Mike Boyd 09/06/21 11:02AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 09/06/21 04:16PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 09/06/21 04:36PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 09/15/21 04:34PM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 09/19/21 11:06AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 04/25/22 05:10PM
  Re: Meddling with a WispRe: Mike Boyd Mike Boyd 04/25/22 06:43PM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 04/26/22 10:24AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 04/26/22 04:41PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 04/27/22 04:49PM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 04/28/22 10:11AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 04/28/22 03:50PM
  Re: Meddling with a WispRe: Graham Motzing Graham Motzing 04/28/22 04:54PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 04/29/22 05:15PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 05/03/22 04:52PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 05/07/22 06:15AM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 05/10/22 11:21PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 05/11/22 03:49PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 05/12/22 04:24PM
  Re: Meddling with a WispRe: P D P D 05/12/22 05:47PM
  Re: Meddling with a WispRe: Graham Motzing Graham Motzing 04/27/22 07:09PM
  Re: Meddling with a WispRe: I M I M 05/09/22 04:28AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 05/10/22 03:52PM
  Re: Meddling with a WispRe: I M I M 05/11/22 09:22AM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 05/12/22 05:00PM
  Re: Meddling with a WispRe: Simon Williams Simon Williams 05/15/22 05:04PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 05/16/22 03:52PM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 07/25/22 02:20AM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 07/25/22 02:36AM
  Re: Meddling with a WispRe: Tom Boyd Tom Boyd 07/25/22 04:55PM
  Re: Meddling with a WispRe: Jay Rivett Jay Rivett 07/26/22 10:42AM
  Re: Meddling with a WispRe: ◕ ‿ ◕ ◕ ‿ ◕ 07/29/22 04:36PM

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