Decking Batavus head

Before I take too much off, I’d like to share my plans. The lip between gasket area and the dome, is about 0.065-0.070. I was going to start with taking off 0.020. Idk chime in if you know better.

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Re: Decking Batavus head

Are you cutting it for higher compression or better squish?

Re: Decking Batavus head

Shooting for higher compression.. wiki doesn’t really say exactly how much. I went ahead and took about .025 off to start.

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Re: Decking Batavus head

Joe Schuitema /

Here's some pics from my batavus build. The first shows the huge squish height. This is because the piston sits about 0.160" below the top of the cylinder. I machined the top of the cylinder so the piston was about 0.020" below the deck. The piston would hit the sparkplug if you did this because the head dome is so shallow. To make a better head design, I added material to the head and reshaped it. I kept the combustion volume about the same. With an upgraded carb and slight port massaging, I got decent acceleration and a top speed around 30-31mph with stock exhaust.

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Re: Decking Batavus head

Brandon Weiss (Detective brandon to you) /

that cutter looks real fly man

Re: Decking Batavus head

That head is super nice. Did you put it in a 4 jaw to do that? I don’t have the ability to add material. I took the cylinder down to the first fin. Also the little nub in the piston skirt.. thinkin about buzzin that off.

Re: Decking Batavus head

Joe Schuitema /

I used a collet in the lathe and a turned steel rod that goes through the sparkplug hole. A countersunk screw holds the head onto the rod. You should be fine with sparkplug/piston clearance if you stopped at the first fin. I went past the fin. Crazy how these things were built.

Re: Decking Batavus head

You can also just turn spark plug threads onto a rod and chuck that up in a lathe.

Re: Decking Batavus head

Yea yea that is actually how you should cut it because it will center the dome perfectly around the plug.

Works good for countersinking heads too. I remember asking my machines guy how he pulled it off and I was impressed by the simplicity of the tool he made.

Re: Decking Batavus head

How are you cutting the dome? A reversed ball turning set up? Thanks for the tips!

Re: Decking Batavus head

Joe Schuitema /

I did a multi angle cut then blended it.

Re: Decking Batavus head

i made hundreds of heads with the metal base of a spark plug cut off and welded to a mandrel... crude but incredibly effective.

cutting the top of the batavus cylinder off is a must, you'd be through the fins by the time you counter sunk that head enough to make it work.

plus the squash band in them is terrible, the worst, the m56 head is a much better starting point but the fins hit on the hs50 IIRC?

Re: Decking Batavus head

So without reshaping the head, decking the cylinder is probably going to cause over heating? I could reverse the compression a little with a head gasket right..

Probably one of the sketchiest lathe operations I’ve done btw

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Re: Decking Batavus head

haha yeah, i shot a vespa cylinder at my face one time but the batavus skirt is pretty heavy duty... at one point i was doing these for people so i made a nice lil' mandrel.

the batavus is so low performance that the head squish band being terrible probably doesnt hurt the heat thing but its definitely robbing power. Its such a bad shape i don't think you can even get in there to cut it better if you wanted to.

Re: Decking Batavus head

Got it all back together with an unmodified head, and no head gasket. sounds poppier at idle. If I gain 2mph out of it I’ll be stoked.

Re: Decking Batavus head

i use a similiar fixture in my lathe. just a threaded rod with 14mm sparkplug threads on it. works great

Re: Decking Batavus head

yeah speed wise you can port an m56 and get it really rippin but it will never get out of its own way accel wise until you fix the compression thing. even putting fuel line in the spring, helps a little but not enough.

Re: Decking Batavus head

It’s still pinned at 25.. and dog shit slow off the line. Found some aluminum balls on Mcmaster Carr. They’re slightly under size. Also thinking about over boring the cylinder. I’m not sure what piston would work for that tho.

Re: Decking Batavus head

Why not just get the bat/morini kit and be done with this?

Re: Decking Batavus head

I have 7 other mopeds I would rather throw a kit on. I’m just messin around with the mobat.

Re: Decking Batavus head

Throwing a kit on a Puch or tomos is so boring though.

Re: Decking Batavus head

Joe Schuitema /

https://www.treatland.tv/ProductDetails.asp?ProductCode=43.5mm-airsal-piston-060306435

I used this piston and bored out the stock cylinder. The ports were massaged a bit but nothing major. Cost me $40 for bore and hone, so I got a fresh top end for $90. The extra 10cc helped the low end.

Re: Decking Batavus head

Hell yea I’m gonna grab that. I own a small jig boring machine, so I’ll be able to at least try it myself. Did you keep everything else stockish?

Re: Decking Batavus head

Joe Schuitema /

I upgraded the carb to a 13.13 dellorto sha and kept the stock pipe. I made a custom intake to match the new carb and opened up the stock reedblock.

Re: Decking Batavus head

My first bat I put a m56 top end on it, works great. Second bat put a morini kit on it. Third bat put a Peugeot engine on it. Just for some variety, I like riding them all. On the first two for the clutch I just took all of the ball bearings out and put the spring back in empty, works just fine.

Re: Decking Batavus head

Bill Mazzacane /

Alex,

I like to have "expected results" before I start any work. In your case do you know what the stock geometric compression ratio was??

Calculating the cranking compression is is better than most compression gauges. The majority of compression testers are not accurate, and frequently read 30psi low. Only a Snap On compression gauge can be trusted.

Your readings will be even lower than that if you didn't kick the piss out of it, or you used the electric starter with less than fully charged battery, or your starter motor is worn out and always cranks slow.

Calculating the cranking compression with the geometric compression ratio (CR) is easy math: CR * Air Density in lbs/in^2. A close approximation can be found by multiplying 15 * CR. For example: 12:1 CR * 15 = 180 psi.

Next important detail is the squish clearance. A proper squish clearance is .030" to .040." A tight squish prevents detonation, and increases performance. It may also make it possible to run more compression, if the compression is within safe limits.

When a wider squish is combined with engine mods and especially a larger carb, top end failures caused by detonation, preignition, or detonation that causes preignition is possible.

Bill M.

Detonation destroys, preignition melts.

Re: Decking Batavus head

Hey bill - Yes i admit that was a blind attempt at gaining a little extra power. I plan on boring the cylinder, so I’ve been digging through a few of my books planning my next move. I see the formulas you are talking about in my graham bell. I’ll definitely work everything out on paper before I make anymore cuts

Re: Decking Batavus head

+1 for spring with no balls. Also the sachs airsal piston is what I'm running in my hero kit, it might have better dimensions in a bat, but I dunno what piston pin-crown height you're shooting for.

Re: Decking Batavus head

Bill Mazzacane /

In the future you can cut a bowl shape for the combustion chamber by cutting a radius into a HSS blank. Maybe 1/2x1/2 to start with. Depending on the material of the blank (HSS or Carbide), there are specific types of grinding wheels for a bench grinder to use.

Do your best at drawing the radius, then grind it, and then add relief so the lower edge of the blank does not rub or cut against the head you are trying to shape.

Use emery cloth to smooth the edges.

You can make a spark plug manderal by cutting a spark plug thread into a 1" diam mild steel stock. Make sure there is a 90' positive stop at the end of the threads. Round off the edges of the manderal. Then center the manderal in the chucks. Use a dial indicator and a dead blow hammer to zero in the gasket surface.

When you are calculating the CR, be sure to include the deck clearance and gasket thickness. Get your self a piece of plexi-glass (about the size of the head gasket). Drill a hole in the center (to add transmission fluid or 100% coolant) into the combustion chamber, and another hole at the end of the squish band to allow trapped air to escape. Use a thin layer of grease to seal the plexi-glass and a syringe with at least 1/2 cc graduation.

The squish band angle should match the piston dome radius if possible. I don't recommend exceeding the piston crown radius.

Bill M.

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