Wanted to confirm a few things. I just had my 50v cylinder ported and I want to regain some balls on the takeoff so I'm gonna deck it.
Can someone give me a quick run-down?
I know it takes a long time, you use some type of sandpaper and a mirror or something super flat to make sure it's even. Also Lee told me to rub in a figure 8 pattern... but that won't exactly work on a 50v head, because of the mounting tube.
thanks.
Hold it tight, and write a large figure 8 slowly.
repeat.
Over and over!!!
Go faster and faster.
I learned mine at a machine shop on small parts.
Yeah. Other tips include:
Tape your sandpaper to a piece of flat glass, or better yet, a marble/granite slab of tile from Home Depot (3 dollars) to make sure you sand it flat. Also sand your cylinder top flat to match but don't take any more off than you have to. Just a few passes will work.
Start with rough paper like 80 grit and work down in a couple steps to 320 or so. Don't need to go any finer than that if you use any kind of asket material.
yeah, just go slow, if you get one side too much you'll have air leaks for days. maybe practice a bit with something, before going with the real deal. also you you measure and mark all the way around the lip to let you know how far you've gone and to keep it generally even. I'm fairly certain 2mm's is the threshold of going to far....maybe try 1mm first, then keep going? it's up to you...let us know how it turns out
you can always put some play-doh on the top of your piston put it all back together (spark plug and all), then turn it over once by hand, and see how much room you've got in there.
Check out the HOBBIT HEAD thread.....there's pics
Oh yeah; Only 2 grits were used. A sheet of 80 & a sheet of 220. Count 20-40 strokes, then 1/4 turn, repeat, yada yada, until you get it down to where you want. You do that to keep it even all the way around. Then do figure 8s with the 220. 1/4" thick piece of glass is perfect.
By the way 2mm is 80 thousanths (WAY too much) Even 1mm might be pushing it.
Forget that figure 8 crap, just run the cylinder head back and forth a few times, then turn it 90 degrees and repeat.
Use wet sand paper, keep it wet and against something flat and you should be golden!
Ya that will work! lol
I just did this to my head, looks good.... Does high heat RTV work as a gasket?
Ideally metal to metal. If you need a sealer then you are not flat!
Sfsorrow brought up the point I need clarified. It's a moby head, you can't set the bottom of it flat on any surface because of the part that the mounting bolt goes through. So, it's okay to just go back and forth?
Thanks for the advice!
don't worry about it, just do it! you can't go wrong!!!!!
Gonna give this a shot today. I'll let you know how it all goes!
Practiced on my peugeot head, since it can be sanded in any direction unlike the moby head. It's super fucking easy. I took off ~.3-.5mm then had to put it back on cuz I needed to leave the house. Saw a bit of an improvement from just that much. going to finish it up tomorrow.
Then when I have a minute I'm going to take the moby apart AGAIN and deck that head too.
Not sure how far to go though. And since I seem to have some weird after-market replacement 103 head (as it hits the top of a polini high-comp head without gasket), I'll have to chart my own territory.
Can anyone give advice on how far to go with a moby head or what it should look like?
thanks again, this is a really exciting mod.
I din't read the whole thread, but did anyone mention the playdough method? You know, where you put the plug in the head, stuff the dome with playdough, tight the head down to spec, then turn it over by hand? This gives you an exact measure of how much room you have to play with (the thickness of the dough on the tip of the plugs electrode.)
take off just under 2mm. what kind of base gasket are you using?
Base gasket is two thin sheets of gasket paper.
Where do you get play-doh these day??
I think I'm gonna go with something where I an see the progress. Lee, I came in about a month or so ago and told you about how my piston would hit the top of the polini high-comp head with a gasket. I re-built the engine over the summer, the head is probably different somehow. Not sure if the general 2mm rule will work for me.
did more work on the peugeot. Compression went from cold 115-120ish to a solid 150.... my guage is kinda funky, it doesn't hold the pressure, so it's probably higher than it reads. About to go out for the first test ride.
hot comp test is only 120... lost all its balls once it warmed up. what gives!
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