2002 DX150TLRA Ignition -Timing - Number of sparks per cylinder

[99yam40]

I would like to know where cpostis facts came from

[cpostis]

I would like to know where cpostis facts came from

Now I'm getting some where! Maybe I'll get some answers?
Got it from Yamaha Service Manual LIT-18616-01-99.



Wish I had some pics, but when I disassembled my SX150TXRZ, the No. one piston had different casting numbers on the inside of the piston from #3 and# 5 pistons. # 2,4, and 6 had their same casting numbers. When checking specs for piston diameter, found #1 different than 2-6 in the service manual .

2001 SX150TXRZ Yamaha Outboard CRANKSHAFT PISTON Diagram and Parts

If you look at the parts list in the attached link, you will see that it lists piston No."3,5" under 17 as number required "2". It lists piston No."1" under 18 as number required "1".

Yes, in the parts list pistons number 1, 3, and 5 have the same part number. Could it be Yamaha now allows the standard piston for # 3 and 5 to work with # 1 for whatever reason?

Even so, why would Yamaha have different piston diameter ranges specifications for no. 1 and for 2-6?

Bewildered?
Chuck

[pstephens46]

Does this affect compression measurement?

[zenoahphobic]

Does this affect compression measurement?

I would not have thought so, but having said that do compression reading ever be exactly the same! Some are satisfied with a 10% variation!

Clearly, now that I have seen the specifications, Yamaha design engineer had allowed for greater heat expansion for that No.1. This also somewhat supports why ignition timing maybe different.

Different componentry when the same is expected occurs all the time (or did). Yamaha doing it? Maybe done to allow engine to be used where reliability of the fuel used can be suspect? e.g. overseas market in developing countries.

[zenoahphobic]

Can we read something into the appearance of that crankshaft drawing?
The conrod journals for No 1 and 2 seem to be at the same crank angle spot, when you see differences between the others.

Some up, some down, some 180 degrees apart. Velly interesting!! Could this have been drawn better?

[cpostis]

I would not have thought so, but having said that do compression reading ever be exactly the same! Some are satisfied with a 10% variation!

Clearly, now that I have seen the specifications, Yamaha design engineer had allowed for greater heat expansion for that No.1. This also somewhat supports why ignition timing maybe different.

Different componentry when the same is expected occurs all the time (or did). Yamaha doing it? Maybe done to allow engine to be used where reliability of the fuel used can be suspect? e.g. overseas market in developing countries.

Zenoahphobic, thanks!

Good theory, however I wonder if I could get direct answer from Yamaha somehow? Maybe if I called Kennesaw customer service?

Rodbolt, do you have any input on this, please? This is just buggin' the heck out of me, and now I have to know!

[boscoe99]

If you call Kennesaw customer service you will be lucky if you get a guy on the line that knows what an OX66 model is. He may or may not have heard of a crank shaft. He will have a glazed look on his face if asked about the piston and cylinder diameters.

All of the engineers are in Japan. They don't speak English. They alone may or may not know why the manual says what it says.