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12G940 Sinking the valves

Posted: Thu Jul 30, 2009 8:40 pm
by Declan_Burns
My mate Günther who restores motorbikes and is heavy into car rallying, sunk the valves on my 12G940 last week. This very expensive piece of kit used is made by a company called "Hunger" based in Munich. I never heard of them before. I was very impressed and just thought I'd post a few photos for general interest.
http://www.ludwig-hunger.de/_english/_p ... 84190_6259[/img]<br><br>Image<br>

Posted: Fri Jul 31, 2009 10:17 am
by 8009STEVE
Nice bit of kit.

Posted: Fri Jul 31, 2009 10:50 am
by bmcecosse
Crikey - we just used a pillar drill and a 45 degree countersink! The special tip was to put a little piece of emery paper under the cutter which stopped it chattering. Result was lovely grey smooth seats. That does look very fancy !

12G940 Sinking the valves

Posted: Fri Jul 31, 2009 11:47 am
by Declan_Burns
Yes, it very fancy indeed. Günter got it as a golden handshake when he retired from Toyota a few years ago and opened up the bike restoration business. He probably would never have bought it himself at 2000 pounds+. Having said that he does use it a lot. I just found it facinating and thought I'd post up some photos.

Posted: Fri Jul 31, 2009 5:07 pm
by bmcecosse
Hope you smoothed away the resulting ridge around each exhaust seat - with small grind stones ?

Posted: Fri Jul 31, 2009 5:59 pm
by MarkyB
Did he cut 3 angle seats while he was at it?

12G940 Sinking the valves

Posted: Fri Jul 31, 2009 6:13 pm
by Declan_Burns
Yes, we actually discussed the ridges this afternoon and yes it will be done.
Yes three angle seats done.

Posted: Fri Jul 31, 2009 8:11 pm
by rayofleamington
Nice to see it being done properly :D

Posted: Fri Jul 31, 2009 8:17 pm
by bmcecosse
I see it's a 'big valve' head - what engine is this intended for ??
And remember - if the exhaust valves have been 'sunk' by 40 thou - then you will need to put 40 thou packing (ie a ~ 40 thou/1mm washer!) under the exhaust valve springs to keep the same compression as the inlets.
Exhaust valve seats should just be single cut - for very best heat transfer from valve to head. The 3 angle thing is more for inlet valves - but a very narrow 'pencil line' seat with smooth blending either side is even better!

12G940 Sinking the valves

Posted: Fri Jul 31, 2009 10:03 pm
by Declan_Burns
Roy,
I wasn't aware of the single cut on the exhaust valves. We've already done the three seat cut. Günter suggested going for a 1mm contact area between valve and seat. That's what we've done. It's for the 1098cc engine with the HIF 38 carb, AAA Needle, Mg Metro inlet manifold and K&N copy air filter-already mounted and engine running very very well indeed for the last three months. I'm quite happy with the performance as it is with the original head but I'm keen to see the difference with the 12g940. It's all an interesting learning process. I'll fit a washer as you suggest to balance the compression-thanks for the tip-sounds logical.

Posted: Sat Aug 01, 2009 4:40 am
by bmcecosse
3 angle seats on exhausts are all very well for racing engines which are regularly stripped and valves re-seated. For normal use - a wider seat is better/longer lasting on the exhausts. But your 1mm (40 thou) seat will be fine - don't worry about it! You only need to fit the washers if looking to REV the engine - otherwise the springs will be fine up to 5500 maybe even 6000 before bouncing - and it's better to bounce the exhausts before the inlets anyway!