Hi Louis.
Thank you for having measuring the cone. Yes, it is very hard to measure.
About the exhaust, maybe I´ll change to aftermarket silencers. Maybe it is easyer just to do that then working with the std. ones.
And... a bit more regard the rebuild of the little 3MA.
I wanted to do a bit more research that could reveal a bit more about the engine, and it´s condition.
A big question mark is the question if I would be doing more bad then good, by starting replacing parts by new...
F.exe. I´ve once changed crankseals on a bike, just because "it would probably be wise", not because there were any sign that they were bad. Result, the one ones (from yamaha, in a yamaha marked plasticbag) one was leaking within a months use...
I started the bike when it was still all together, idled OK, not too much smoke, etc.
I decided then to get the engine measured through, and then decide if I would go for a full rebuild, or if that simply was not necessary.
First of all, calibration of the instruments. When measuring 100s of a milimeter, calibration is paramount.
The micrometer was calibrated.
The bore gauge was also calibrated, using the calibrated micrometer.
That done. I started measuring the cylinders. This is very hard to measure at the places that the manual says... actually impossible. No good measurements can be taken from the top of the exhaust port, to the bottom of the transfers boost port.
Both cylinders measured, I started measuring the pistons... again, the manuals (or as I undestand it, not because I can read japanese... just by looking at the number
) 5mm from the piston skirt. Impossible on this piston because the cutout at the intake side goes higher then 5mm, so I measured at the point where the cut out stops.
Ring gap was off course also measured.
Also performed the "searchblade" test (inserted between piston and cylinder)
Next, measured the crank. It was very, very acceptable, everything!
Then, I opened the clutch side cover, to measure the clutch. Again, very good results.
Here are the cylinder/piston measurements I took:
Measured Manual
Right cylinder 56,05-56,06 56,00-56,02
Left cylinder 56,045-56,06
Right piston 55,98-55,99 55,95-55,98
Left piston 55,985-55,99
Blade test 0,5
Ring gap right
3mm from top 0,45
10mm from top 0,4
Ring gap left
3mm from top 0,5
10mm from top 0,45
After having taken the measurements, and referencing them to what the manual prescribes... I started scratching my head
Cylinders are marked C... and pistons are marked M
Both cylinders and pistons have greater measures then manual prescribes...
Then I looked, pistons are marked 2XT00, and cylinders 3MA00. From what I read here... it does not add up. I´ve read 2XT00 pistons are for the SP??? and have a lower (flater) dome at the top?
I was curious... so out I went to buy some chewing gum
Chewing gum placed 4 places in the combustion chambers squish, and pressed with the piston, to see if the squishband area was of consistent thickness. It was, so in my bike anyway 3MA00 cyls and 3MA00 head goes good with 2XT00 pistons.
This also meant that I could not use the measurements from the 3MA00 manual as reference.
I ended up with the folowing results for bore/piston clearence.
Both left and Right side - Max. clearence 0,07mm Min. clearence 0,06mm
Maybe this would not be acceptable for a 56mm piston,
BUT when taken into consideration that measurement of the piston should have been taken at a place 5mm lower, I think these results are very good.
Both pistons and rings will be used again.
On to the measurements I took on the crank. Again, very good. See picture below.
And last, but not least, I measured the clutch.
Well within specifications.
1st friction plate - 3,6mm - manual says (or at least what I can interprete) 3,4-3,6
Rest - 3-3,05mm manual 2,9-3,1
Springs - 39,7-39,9 manual 38,1-40,1
So... IMO, very good results all the way. This engine has very little fatige, wich corrobarates the kms shown on the tacho.
I will put the engine together again, with new gaskets, but will not change parts. That would be in my opinion a waiste of both money and good OEM parts. And I would be trading OEM parts in good condition for non OEM aftermarket parts.
I gave the parts I had out, a good clean up, pistons, clutch plates, oilpump net, etc etc, and when the new gasket set comes, I´ll close the engine again.
An interesting thing I noticed. The oilpump gear is the one that spins the gear for the gearbox oil pump. Do you guys have a trick to how to run the gearbox oil pump while removing the 2stroke oil pump?
And, last but not least, "
if you don´t have pictures, it never happened." Isn´t that what they say?
Unfortunatly my phones bat when out and I didn´t take as many as I would like to have done.