Hi I'm Dave welcome back to AuMechanic Channel
I showed you this little cheap
engine and I bought off ebay the 49cc engine so I'm going to show you how to
measure up a couple of things port mapping compression ratio so forth so on
the reason we need to do that not just for this engine but for any two-stroke
engine if we're going to do any modifications or we've got to measure
everything up so that we know which part of the engine is deficient you know and
what actually needs modification on it because if you're going to get you know
your best bang for your buck if you're going to do some work to it you want to
find out where the engine is most deficient and then when you do that
single modification you get the most value out of your work yeah and then
other modifications might need other modifications but you know this each
modification has different returns and you know you usually start with the one
that's going to give you the most you know improvement that's the first thing
second thing is there's a couple things that with this engine that are not quite
white so if you've got one of those small engines that might also interest
you so we'll do a couple of things to reveal a few issues with this motor so
the first thing that's wrong with this engine this is two main faults for this
engine one is that the small end bearing to the hangs each side of the con rod
I'll show you that, the other problem is is that this piston just doesn't go
anywhere near the bottom of the port at bottom dead center you see
and that's not too good push that down yeah that's bottom there a
couple of things we want to measure is the piston clearance from the top of the
head because this cylinder head is not removable so when I'm doing the
measurements I need to know what that is so I'm going to show you a quick and
easy way to measure the piston clearance from the top but what we've also got
with this motor is is this piston doesn't go all the way down so what I'm
going to do before I take it apart is I'm actually going to use a marker and
I'm just going to mark this you see a piston there so the once I take it off I
can actually meet you measure what the heart is there so
I've got a piece of solder here you can use a thicker piece of solder we're
gonna actually use that to squish it against the top of the cylinder now
because we haven't got a removable cylinder and normally if you're going to
measure the clearance you want to lay it all the way around the cylinder all the
way around the piston because if you just measure in one side the piston can
kick over and give you a false reading so you want to put or at least put two
pieces one side and the other side or all the way around the piston without it
I'm not on top dead center just put it all the way around the cylinder like
that you know a ring of the solder so that when you bring it up the top dead
center in you and you squish the piece of solder you can measure it a couple of
places and make sure that you've got the you know the average clearance of all
the parts in the cylinder because if you just measure it once in one spot then
there's a side the piston has got a little bit of clearance in the bore now
I'm just gonna I've got a light there I don't know if you can see it but I can
see it in there and I'm just gonna take that up I've pushed it against the
cylinder wall then I'm gonna take that up the top dead center and now I'm just
gonna push that down on the piece to push it on this side so the cock it over
this side like that just make sure that you know if if the piston is pushed over
that side so we get the the absolute minimum amount okay we don't to read
the largest about tolerance we want to meet the minimum of our tolerance I just
push that down and then I'll take that out of there and then what I'll do is
that's you probably can't see that but that is squash down it's got a little
bit of squash bit on the edge and I will just measure it the calipers and I get
0.6 of a millimeter now that I spoke about before with this
you see the small end bearing okay just hangs outside so so if the piston I mean
the piston's held about center of the rod you know when the cylinders on but even
so the bearing can hang out a bit and that means the roller isn't isn't full
width the roller is sort of on one side so it's it's you know the stress on that
rod is off-center so that could be a problem for the rod and also that you
know this can you sort of float from one side to the other it's just generally
pretty shonky and could have been easily resolved by whoever built the engine the
manufacturers by just putting a little aluminium washer each side of that now
you can see the line from the that I marked so that's the difference between
the bottom of the port the bottom of the exhaust port and the top of the piston
at the top of the piston should come down to the bottom of the exhaust port
and but I don't think that's normal for these engines so I'm just gonna measure
measures accurately as I can bit of an angle there but it's three millimeters
if that's the 34 mil stroke then for the piston to go all the way down the top of
the piston to come down to the bottom of the port we had three that would have to
be off an engine that had a 37 millimeter stroke so I don't know if
there's any of these engines that have a 44 mil bore by 37 millimeter stroke or
44 by 36 millimeter stroke if anyone's familiar with these motors yeah let us
know if these actually come with a with a 44 by 36 or 44 by 37 this
one's 44 by 34.
The next thing we're going to do now that we've measured
we've got three mil on there we've measured the piston clearance from
the top of the cylinder is we're going to move to the cylinder and we're going to
take some measurements off the cylinder so I think that will do it for now
and we'll leave the rest until the next video bye for now folks