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[simon]

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[simon]

Failed in an attempt to show a Ducati 860 Cylinder head which has a nice obvious squish band.

[simon]

http://www.mez.co.uk/mezporting/ducati_b.jpg
Here's the link

[Bullet Whisperer]

It is possible to lap the faces in and run without a head gasket, but the gain to the compression is tiny, if going up from the std 6.5:1 or so, you probably won't gain very much. On a 350, 1mm of gasket space removed will give just short of 4cc chamber space reduction over the piston. For a 500, it will give a reduction of 5.5cc.
As an example, if you already have a 500 set at 8.14 :1 [70cc combustion chamber space] and you remove 1mm by doing away with the head gasket, you will end up with 8.75:1. The higher the C.R. to start with, the greater the gain will be as the reduction of either 4cc or 5.5cc becomes a bigger proportion of the combustion chamber volume you are starting with. A 350 at 6.8:1 will only reach 7.25:1 with 1mm removed by doing away with the head gasket. On the machines I tune, I usually shorten the cylinder barrels as well and for the record, there are several 350 and 500 Bullets out there, running at up to 10:1 C.R. with no problems [or fuel additives] and one Crusader road / sprint bike residing over at the I.O.M. with an initial accidental 13:1 C.R., which I thought might have to run on methanol, but ordinary unleaded worked fine, so I left it on petrol. that one is VERY fast !!
My squish band modification has been used successfully on the racing Enfields and one of the 'Asbo' Bullets may be getting one soon as well. Regards, Paul.

[Nettshubby]

Tom, if I was still at work, (retired),I could have matched them up. I do have a small lathe / miller, but am not set up with face plate yet, or a rigid milling table.
Ideally the gaps on both spigot and gasket face should close up with whatever gasket thickness one chooses. i would rather the gasket is clamped if it means a small gap on top of spigot, as mine was when I stripped it.
Ray.

[ChrisD]

Hi Tomshayes. Yes, I did it on my modified 1996 535cc and it has proved extremely successful. No, I didn't do it for the extra oomph of the fractional compression increase (I actually took 1.5mm off the head anyway), I did it to help remove heat from the top end. I live in South Africa and summer days can often surpass 40degC, so the top end was getting very hot in town. I did find that the head locally weeped oil but then I had viton O-rings placed in carved rings around the pushrod tubes in the alloy barrel. No heat problems anymore - well I also twin-plugged it to get a faster burn to remove more heat and fitted high capacity oil pumps.
I actually brush on a thin film of Wellseal but find it all squeezes out because, luckily, both surfaces fit very well. Had it machined close to perfection, then lots of lapping of head and spigot on emery paper on plate glass - special glass disc cut to fit into the head recess too. Took a long time but is well worth the effort. Cheers, ChrisD

[Tomshayes]

Thanks Bullet Whisperer / Chris D etc.

I am running a 91 350 and want a little more oomph on hills etc.. I'm not looking for blistering acceleration (It is a single) or warp factor 12 but a tad more pulling power.

Thanks for the advice

Tom

[Tomshayes]

Further to my post.

is there any great advantage between fitting the Higher Cop Piston over the Forged piston (350) as supplied by our hosts, other than the £100 difference to Mr H?.

The Higher Comp piston is considerably lighter than the Std piston..

Tom

[Alan R]

Hi guys----------with regards to removing some of the barell spigot}--- I did mine by handfile !! --- I Kid-you-not but it can be done and accurately too..Ideally when the gasket id fitted and compressed fully the lip should just be a "nats nudger" shy of the head, thus ALL compressive forces are directed onto the gasket....

[simon]

I've got the Hi Comp 8:1 piston ( not forged) in my 350 and it seems to be excellent to this point anyway. I've got a bigger carb with a ported head and the improved cams and it does go very nicely. I've also got the aluminium barrel which makes sustained use of speed more viable. The next mod would be an larger capacity oil pump and possibly a roller bearing big end. It is a delightful round town bike and is ok on the open road but on the motorways it could use an extra 150cc. The long stroke crank mod looks good but as it's a bitsa and therefore has no provenance and little value so I struggle to justify spending the large amount of coin on what is as t is a perfectly satisfactory 350cc motorcycle.