1SlowVW HalfDork
4/24/22 7:42 p.m.

So I have this head of my racing outboard, heads are few and far between and I've got two bad ones. This is the one I ran last year but as you can see the squish band on one cylinder is buggered from playing pinball with wrist pin bearing bits. 
How could I make a tool to recut the flat section (squish band) around the dome.

My idea, see the plug mounted in the photo. If o mounted a stud there how could I securely fasten an rotary tool to recut the band? I don't mind loosing a little compression and I could always plane the head to compensate. 


Yes this could be done on a mill, but I don't have one and my friends with them are backed up with paying work. 

1SlowVW HalfDork
4/24/22 8:26 p.m.

Option two:

Still have a centering stud in the plug hole but just turn a big piston with a hole in the middle out of steel. Have the "piston" with the proper angle cut to the surface I want to refinish. 
Spin the slug by hand or with a drill and let valve lapping compound do the grinding

11GTCS Dork
4/24/22 8:33 p.m.

Is a weld repair and remachining of the head a possibility?  I suppose not if that void area is a water chamber? 

1SlowVW HalfDork
4/24/22 8:40 p.m.

In reply to 11GTCS :

There are shops that can do it, but it's sensitive because coolant runs through the head and mine have been run in salt water as well. 
Also that's an expensive option. 

These motors are only "worth" maybe 2-3k for a top running one. So spending 500$ getting a head fixed is a tough call. 
If I can recut the band , even if it takes a lot of personal time it's worth it to me. 


Slippery GRM+ Memberand UberDork
4/24/22 8:46 p.m.

Are you trying to get rid of the hot spots?  I would honestly just free hand it with a Dremel and a grinding bit, just smooth it out. 

1SlowVW HalfDork
4/24/22 8:51 p.m.
Slippery said:

Are you trying to get rid of the hot spots?  I would honestly just free hand it with a Dremel and a grinding bit, just smooth it out. 

Yes, in fact here's a before photo. This was after smoothing and running for one summer. But I want it to be better and having a tool that could do it repeatedly would be really great. 

1SlowVW HalfDork
4/26/22 2:37 p.m.

Progress is slow but a friend with a lathe made me a large stud to use in place of the plug above. 
He's a hobby/farm thought machinist. He took the head with him and said come see him in a few days. We'll see what he dreams up. 

Tom1200 UltraDork
4/26/22 4:09 p.m.

In reply to 1SlowVW :

Look up Stan Stephans  articles in Classic Motorcylce Mechanics on the internet (British publication)

Stan ran a series of articles on how he repaired this type of damage.

1SlowVW HalfDork
4/26/22 5:13 p.m.

In reply to Tom1200 :



bentwrench UltraDork
4/27/22 1:00 a.m.

With karts they use a mandrel that screws into the plug hole to spin the head from the side opposite the chamber in a lathe.

Are those inserts?

Otherwise you will be speed limited, unless you can support the offset mass.

How do they do the banshee heads? I believe they have inserts?

Machine your head to accept an insert?

Otherwise a 3 axis CNC mill can churn those out......

1SlowVW HalfDork
4/27/22 8:33 a.m.

In reply to bentwrench :

They are not inserts, we did consider making a bushing and pulling it from the top side to machine it. We'll see what v1.0 looks like when my neighbour comes back. If it doesn't work we'll try something else.

Obviously a mill is the answer here, then fly cut the mating surface to get the cc back to legal...but I don't have a machine shop so we're trying to get creative. 

1SlowVW HalfDork
4/28/22 8:22 p.m.

They see me grinding my squish band but they don't know I'm causing uneven compression between cylinders that I'll have to fix later.

1SlowVW HalfDork
4/28/22 8:23 p.m.

1SlowVW HalfDork
5/1/22 4:41 p.m.

This is cleaning up nicely . 

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