Squish
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Hi guys
Just got my new barrel back from Micky, also got a 3mb head for cheap been skimmed before so want to check squish but can’t find manufacturer specifications for the clearance from piston to head
Any help be great thank you@OllieDTR A. Graham Bell's two-stroke tuning book discusses this, I just had a quick read and he recommends 0.6-0.8mm squish clearance on a 100-125cc engine. Most people measure this by laying a length of solder wire across the piston crown then fitting/torquing down the cylinder head and carefully turning over the engine before taking off the head and measuring the thickness of the solder with a digital vernier.
Unfortunately this means IMO you'll need a brand new head gasket the same as the one you intend to use just to measure the squish (the DTR is one engine which won't benefit from trying to re-use head gaskets), unless you can devise a way to be absolutely certain the solder has reached the edge of the bore when measuring. Lidl sell those internal cameras for looking into these kinds of spaces, if there's room for the business end of that and the solder wire down the spark plug hole you might be OK.
Bell also cautions that if you optimise the squish clearance, due to the difficulties of achieving precision in mass production it might change if you do any further engine work like replacing the piston, gaskets etc. so most manufacturers opt for a fairly sloppy squish clearance to allow for this. But if you're happy to measure it every time you build the engine that's no problem and you could pick up a noticeable power increase. It's well worth getting this book:
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@OllieDTR A. Graham Bell's two-stroke tuning book discusses this, I just had a quick read and he recommends 0.6-0.8mm squish clearance on a 100-125cc engine. Most people measure this by laying a length of solder wire across the piston crown then fitting/torquing down the cylinder head and carefully turning over the engine before taking off the head and measuring the thickness of the solder with a digital vernier.
Unfortunately this means IMO you'll need a brand new head gasket the same as the one you intend to use just to measure the squish (the DTR is one engine which won't benefit from trying to re-use head gaskets), unless you can devise a way to be absolutely certain the solder has reached the edge of the bore when measuring. Lidl sell those internal cameras for looking into these kinds of spaces, if there's room for the business end of that and the solder wire down the spark plug hole you might be OK.
Bell also cautions that if you optimise the squish clearance, due to the difficulties of achieving precision in mass production it might change if you do any further engine work like replacing the piston, gaskets etc. so most manufacturers opt for a fairly sloppy squish clearance to allow for this. But if you're happy to measure it every time you build the engine that's no problem and you could pick up a noticeable power increase. It's well worth getting this book:
@HOTSHOT-III Ahem remove the cylinder with the head intact to not having to keep replacing head gaskets...I.e. undo the base nuts and remove the engine.
When I swap between cylinders, 170/3MBP/3MB/4FU, I do this. This at least leaves the head gasket intact. It can be beneficial to drop the front engine mount to give you more wiggle room, but I've always managed okay without this.
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All done cheers guys, running 0.9mm of squish on my new 3MB head,
Also dremel the intake rubber so my tm32 fits now! Just need to find someone who’s selling a decent carb to airbox rubber so I can fit it, as mine on the bike is perished and no way stressing over the end.
@Calum you run a pod filter don’t you? I was thinking of doing this but ain’t they really hard to jet?
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All done cheers guys, running 0.9mm of squish on my new 3MB head,
Also dremel the intake rubber so my tm32 fits now! Just need to find someone who’s selling a decent carb to airbox rubber so I can fit it, as mine on the bike is perished and no way stressing over the end.
@Calum you run a pod filter don’t you? I was thinking of doing this but ain’t they really hard to jet?
Not terribly convinced. They sent me home on a completely broken/dangerous bike...