I've been told that my MK 1 Mugello 225 head is "Reaper tuned" to 10.5 : 1 compression but apart from matching up inlet & exhaust to the manifolds it's had no further tuning, so it should be lowered to 9.5 : 1. How do I go about it? Does all material have to be removed from the bowl or can I remove a small amount of the squish machined part to make the bowl wider as well as deeper?
Also posted on LCGB.
Any tips on lowering cylinder head compression
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bristolmod
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2 head gaskets as per original SX150?
Chris
Chris
Scootering since 1968.
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ScooterLoopyJohn
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From what i have seen of these heads your best bet is to start with a new 200cc indian head and recut the bowl and squish band to exactly match the piston radius. By this i do not mean a staight turned angle but a correct radius cut to suit. done the last 6 engines this way all with good results. pm for details. PS the new bowl and squixh band is CAD drawn and then CNC 3D milled into the head. For small block engines i start with a 125 head and big blocks with a 200cc indian fat head. Very good for 186 mugello engines as the original heads are way off.
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dirtyhandslopez
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ScooterLoopyJohn wrote:From what i have seen of these heads your best bet is to start with a new 200cc indian head and recut the bowl and squish band to exactly match the piston radius. By this i do not mean a staight turned angle but a correct radius cut to suit. done the last 6 engines this way all with good results. pm for details. PS the new bowl and squixh band is CAD drawn and then CNC 3D milled into the head. For small block engines i start with a 125 head and big blocks with a 200cc indian fat head. Very good for 186 mugello engines as the original heads are way off.
Good to know, thank you.
Was wondering what to do with all those 125 heads on the shelf.
That's not going anywhere...
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corrado
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As SLJ pointed out elsewhere ........bristolmod wrote:2 head gaskets as per original SX150?
Chris
But then you lose the squish band which needs to be 1-1.3mm to work well. Its all about the heat in the piston being transfered to the head which stops working well over 1.5mm squish.
can you not increase the volume with a ball type grinder bit.......or buy the right one you tight ass 
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corrado
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I only had one day to work on it, Sunday, all the cylinder head shops were shut.cezeta wrote:can you not increase the volume with a ball type grinder bit.......or buy the right one you tight ass
I've got plenty of lower comp heads (TS1 / RB) but the Muggy head is machined so that it sits inside the cylinder.
Did what I could with a dremmel but didn't want to go mad and possibly make things worst. I should have taken before and after cc measurements of the bowl but needed a syringe to do it accurately and I didn't have one.