The BSA A7-A10 Forum
Technical (Descriptive Topic Titles - Stay on Topic) => A7 & A10 Engine => Topic started by: mugwump on 12.02. 2016 14:50
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This may already have been discussed in the forum so apologies if this is a repeat. On stripping my recently acquired basket case Ariel H'master ( hope I'm allowed to mention said marque as its so closely associated with the A10 ) I found the oil-lway from the PRV up to the cam trough blocked. Now, this was blocked by the cross drilling plug and therefore blocked by the factory. I know those cynics out there will argue that it must have been blocked by debris etc. but it most certainly wasn't. It was impossible to pass air or any liquids via this route. I drilled the front of the crank case and using a spoke determined where the block was. No amount of force would clear it. Not having a long drill bit, it may have broken anyway ( nightmare) so I then drilled the face of the crank case where the factory fitted plug is next to the small oil jet which sprays the pinion. only alluminium material was removed and blockage cleared. This oil-way is supposed to feed the cam trough on initial start-up when the PRV opens under cold oil pressure. It not having performed as it should have is, I believe, a major cause of the badly worn and subsequently re-built cams and followers I'm saddled with as they can only have been oiled by splash etc. Perhaps this is a one-off or just a rare occassion when the offending plug was driven in too hard or a too bigger hole, who knows. I sometimes hear the oil hole in the cam trough referred to as a drain too, its clearly a feed to the trough.
Hope this has been informative and not just covered old ground.
Accompanied pics to illustrate the above.
http://imgur.com/eajvEsU.jpg
http://imgur.com/n9aUYeY.jpg
http://imgur.com/WXwXTWc.jpg
http://imgur.com/FcuVddP.jpg
http://imgur.com/Xo7kNKL.jpg
adm edit: added pictures as attachments.
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This oil-way is supposed to feed the cam trough on initial start-up when the PRV opens under cold oil pressure.
does the PRV not open with higher revs, unless the Huntmaster is different than an A10 then that plug might be a user addition as I don't have one on either of my A's
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Hi Bill, I imagine the PRV would open with higher revs ( not had bike running yet ) but the oil still has to flow from the PRV up to the horizontal oil tunnel and the across to meet the tunnel going up to the cam shaft. I mentioned this episode as I believed the A10 c/cases are same as Ariel??. Where the two oil tunnels meet ( cross drilling ) MUST have an alloy plug fitted at this junction or oil would simply p**s out into the timing cover and not reach the cam trough. The plug isn't readily visible as it is ground flat (and merges with the crank case material) to accommodate the back face of the pinion .
I should have said, to make it clear that when the tunnels are factory drilled the drill has to pass right through the tunnel in both directions. The short extended end of the defunct part of the tunnel is then plugged. If you look carefully one can see the plug has been ground flush.
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but the oil still has to flow from the PRV up to the horizontal oil tunnel and the across to meet the tunnel going up to the cam shaft.
OOPS sorry I now see where you are (inside the trimming case) sorry I thought this was around the PVR
Yes agreed and when I had mine stripped down I checked that oil way on both of them and they clear all the way, it also sprays oil onto the idler pinion bushes if I remember correctly, the camshaft tho is running in an oil mist as well as the oil that sits in the camshaft trough