Was having some issues finding a new head gasket for my GJ72a, so thought it might be interesting to try making one myself. Got a sheet of advertised 99.9% 0.8mm pure copper sheet. In retrospect probably would have gone with the 0.5mm, but wanted to err on the side of caution. Drew up the original gasket in AutoCAD as accurately as I could. I didn’t really trust the accuracy of my drawing so I laser cut a test sheet out of paper and compared it to the original and test fit it on the barrels and head to make sure all the passages lined up as they should. All looked good so decided to cut it out properly. Was originally going to use a fibre laser to cut the components but had issues with the machine getting back reflections off the material so ended up just using the waterjet cutter. This left a fairly rough finish around the edge of the part and it took a fair bit of filing to get it looking nice. Used a normal half round file to clean up the bulk of the part and a round jewellers file to access the smaller holes and inside of corners. Went over the holes for the bores with 80 then 120 grit for good measure. I suspect that the offset on the waterjet cutter was slightly off as the holes for the dowels required a fair bit of filing to fit right. I made sure to check that everything (especially the holes for the bores) on the copper part and all looked good right. Before fitting the gasket, I annealed it by heating it up over a camping stove until it all changed colour then dropped it into a bucket of water. The gasket is now on the bike and am in the process of putting everything back together but thought I’d post this just in case I’ve done something catastrophically wrong as I’ve never really worked with copper before.
Be prepared for future gasket failure, the reason being the head bolt torque & the large clamp down surface area will not compress the copper very well. Using Hylomar head gasket spray saved my ass for a while (supercharged Honda MC19),,, I ended up getting a custom MLS gasket made, that solved my problem Tiny
Ah **** right, I'll get hold of some of that Hylomar head gasket spray and see how I go for a little while. Not really planning on pushing it too much so hopefully should last for a bit? Where did you get your custom MLS from, and what sort of cost should I expect?
I've made and used copper sheet head gaskets for a lot of motors. From British twins to Late japanese fours. And a triple or two. Properly annealed, suitable O rings where the OE has them - and a coat of paint - and no problems. I always used to use aerosol Engine Enamel but a customer of mine pointed me at a VHT copper gasket spray paint which seems to be quite good. They must be thoroughly de- burred before use. A hand-held countersink bit is good for round holes. For a blown motor, I've used a 20 gauge stainless wire ring set into a groove outside each bore. With about .004 - .005in projection above the surface these dig into the gasket and provide a very high pressure seal. Only drawback is that you can't reuse the gasket as it's stretched over the wire.
Not made any copper head gaskets myself, but if they work for Greg and Allan Millyard that should be enough. In my experience, the thicker any gasket is, the more useless it is.
www.gasketsolutions.com.au 1 off - head gasket to sample supplied 2.0 mm thick with stainless steel fire rings with valve relief cut outs = $195.80 ea. + GST 2 off - as above = $145.60 ea. + GST Programming set up cost = $50.00 + GST (once only cost). Lead time 7 to 10 working days from receipt of go ahead. Postage = $10.00 + GST
2.0mm thick is car use. Bikes don't use head bolt torque values anywhere near a car. For bikes I've usually used 20 gauge - which is fractionally under 1 mm. When it's been available I've used .5 mm sheet. 1mm is easier to work with 2mm MLS is again too thick for a small bike engine. The squish clearance on an FZR250 for example is usually just over 1.0mm with stock gaskets. Use a 2mm thick head gasket and you'd drop compression noticeably.
It's a good job well done despite the thicker material - colour me mighty impressed! I've got an FZR250 head gasket here which is only ~0.18mm with the rubberised paint - they are stainless Precision shims sells 304 stainless in 320mm x 320mm sheets http://www.precisionshims.com.au/products/stock Wondering if it would be possible to put a thin layer of black paint or otherwise matt the upper surface for laser cutting.
Alright thanks very much for all the advice. Am going to try the Hylomar head gasket spray since thats whats available in my area. We did try and make the laser happy by covering the area in masking tape but the results on a test piece with that method produced a bit of mess on the other side of the material. I'm sure with more time playing around with power and air flow settings it would work better but the waterjet was in the same building and knew it would work. If/when the copper gasket fails I'll give the stainless sheet with rubberised paint ago, that sounds interesting.
That was the plan, drop the C/R down to 9.67/1, the suit 15 lb boost, the thick gasket required some Gyro Gearloose thinking in the cam drive gear cassette dept,,,
From experience, the better way is to use flat-top pistons and keep the squish band clearances at or less than .040in. Smaller, tighter combustion chamber, less spark advance for complete combustion. More power.
I tried, but there's not a lot of decent pistons available. I had methanol buffer , it extended the Chinese piston life by 1%, with the help of a ceramic crown coating (no intercooler. )
