AF16 vs. AF18 engine blocks....

[S4Patrick]

What, if any, are the differences between the AF16 and the AF18 engine blocks?

[Wheelman-111]

Greetings:

All 18s in the US are grey-market imports. Honda ended his 2-stroke run here with the 16.

The boost port size is one notable change. 3x6 on the 16, 6x12 on the 18.

Just as the 16s had running changes like the single/double tranny bearing, all 18s may not be the same.

[S4Patrick]

Thanks for the reply...

SO as for the crank, stroke & possible modifications, they are the same?

That is, an AF18 BBK, would work on an AF16? Pulley and trans mods as well?


Thank you....

~Patrick

[Wheelman-111]

Greetings:

BBKs for AF18 Dio models do install. See Flash 4 build from 6 months ago. You must first enlarge the Boost port using the 18 base gasket as a template.

Variator parts fit without issues, and possibly gears too.

[tw39515]

on some of the af18e one side of the crank takes a smaller seal, but if not mistaken the crank is the same. also the af18e has a crank case port down below oil pump to power the fuel pump since the gas tank was in the floor.

[bakaracer]

Any aftermarket parts for the vertical dio motor will work on the af18e block.af16 to af28 engines share the same aftermarket parts.

[axo]

Mine is AF18..
the crank seals are different. Let me know if you need the part numbers.

[S4Patrick]

Interesting...why do you thin the engineers chose different sized crank seals?

Also, AXO, you gotta post up some pictures of your Dio, The entire bike, the exhaust, and the motor~!


~Patrick

[Wheelman-111]

Greetings:

Quoth S4Patrick:

Interesting...why do you thin the engineers chose different sized crank seals?

Sometimes the Engineers make those choices. Sometimes it's the Accountants. Tooling and casting cost money. If there's a part in the bin that can be made to work, Honda will sometimes use it even if it's not the very best from the Engineering standpoint. "Good enough" and a cheaper price tag is often the chosen path.

If engine failures result from the process, Honda quickly upgrades the inadequate part for a better one, typically. The odd-size seal issue was a 1-year affair, I recall reading someplace.

[axo]

Yeah maybe i should open one of those threads in the build section... i don't see anyone else here with a Dio.
The cut in the case for the boost port is very small stock, i can't imagine the af16 being smaller than what i got here, so if you install a BBK you still need to cut the boost port and replace the seals.. here is the part numbers:

the crank seals are the same size on both sides (15.6x25.5x7). Part 91201-GK8-003

The other seals for the transmission are:
91254-GE8-005 for the seal that goes on the case (24x40x7)
91204-GN2-005 for the one in the small gear cover (17x30x5).

[Wheelman-111]

Greetings:

Sanjuro built a tasty Dio a few months ago, and has researched his build very carefully as I recall.

It's a Very Good Idea to cut the boost port on the cases to match the bore, but why do you say the seals need to be replaced?

[axo]

Greetings:

Sanjuro built a tasty Dio a few months ago, and has researched his build very carefully as I recall.

It's a Very Good Idea to cut the boost port on the cases to match the bore, but why do you say the seals need to be replaced?

Sorry i did not want to mean "must replace the seals"
But because i split the case, it it was cheap to replace the seals with new ones in the process just in case, may be the OP could use the part numbers in the future if he decides to get new ones

[veedubh20]

all af18 has dual bearing gearbox cover, but,, it has differ stock tooth ratios may vary on certain jdm honda scooter ran af18e block..

right af18e crank case only,, it will fit 5 o clock pickup stator from 87,88-93 lx 50

[deuce217]

Nice write up guys! Thanks

[veedubh20]

Some af18 has small spline crank use a small seal on a right case and s bearings, need to make crankcase paper gasket to mate both crank case assembly!
Later af18 block use s crank, s seals n bearings n Honda bond.