Finally Worked On My First Honda 2Ts Today

[90GTVert]

One of the guys that I ride with has a couple of Dio engines in need of work. I’m used to hearing about AF16 and AF18. These were AF 20-something and AF 30-something. Not a clue what the difference is.

One was stock and needed to be cut for a 52mm stroker crank.




I was able to drill 2 more holes in my homemade Minarelli case cutter and make it work with the Dio engine since it also has 20mm ID bearings.




I’m used to complaining about hardly any meat between the case bolt holes and crankcase on my Chinese Minarelli clones, but these things are crazy with these giant cranks. Some bolt holes are opened wide. The fun part of that is that I wound up cutting the threads on the bolts holding the top support of the cutter in order to make the full cut.








It also needs to be cut for a bigger cylinder. I tried to adapt my boring tool to that, but the time it would take to try to make something work is worse than just cutting with carbide burrs.


I turned a pair of old bearings into dummy/mock-up bearings. Otherwise he wanted me to assemble an engine just to check, so I said this is a much better use of time in the long run.


The other engine has been together as a 125cc, but had a crack in the case around the crank. He had another friend weld that up. The weld didn’t fill all the way to the top. Rather than ask for a bit more weld, he sanded the cases to try to flatten it out. Big mistake. I did a pass with the cutter on each case half to finish it off better, but as soon as case bolts are snugged the crank binds up. You can see gaps from uneven surfaces. Now it’s a big job with milling and a spacer if it will ever be right. He’s gonna try to have it milled by a friend and make a spacer himself. We’ll see.

Here’s the gearbox of that one. Some nasty old gear oil in there.




At some point he wants me to install cranks for him. They’re on order ATM. If the sanded cases can't be made to work, now he wants to try cutting the gearbox off of the Dio engine and welding it to a Minarelli because he saw another guy do it and that guy says the gearbox from the Dio is so much faster but the Yamaha engine has less problems with cooling for longer rides. I told him that sounds scary and there are much easier ways to be fast. Tried to encourage him to build something simpler like a Zuma. It's not like he's trying to break records. That's too much work and risk for what it is IMO. He says it's not that bad... but he says that about everything.

[oldgeek]

Nice work! Another feather for your hat. One trick I learned along the way is you should drill and tap the three carter bolt holes that get cut into all the way through to the CVT side of the cases before you start cutting the crank area bigger. It makes the job easier without half of the bolt hole missing. I use stainless threaded rod for those three holes and nuts to secure them on the flywheel side.

[90GTVert]

I assembled the bottom end with a new 52mm crank today. Damn that’s close with the bolts! It clears though and he just wanted me to leave it.




Everything went together without any pressing or pulling. Just hot and cold.




The owner always talks about how these Hondas can’t be ridden long without overheating. I was curious if the setup details were wrong because I’ve built plenty of Minarelli strokers and know that stuff doesn’t always match up as it should and it can cause all sorts of issues.

The piston is flush with transfers at BDC. Exhaust port a little higher, but close. Piston is very near deck at TDC.




I put a degree wheel on it and was surprised how aggressive it is. It’s about 195 ex and 139 transfer. I told him that’s a lot. The exhaust duration is basically the same as the RC1 that’s making its peak at ~13500. I said I don’t think this thing is revving like that and he said you haven’t heard it run yet. I really don’t think it’s doing that though. It’s some gold pipe. I told him maybe look into Arrow, but I really don’t know Honda stuff.

The exhaust port is pretty narrow, but the studs look quite close. I’d prefer to see the ridge near the entry blended.




I’ve emphasized the importance of leak testing to see if that has anything to do with the overheating and he says he will make a tester and do that.


I’m curious to see how it winds up running. Now he’s trying to get another pair of cases for me to cut and install an old crank in.

[monsterunderyourbed]

I have two Dios in the back of my shop I am gonna drag out soon in my effort to have everything I own operational and boogying down the street. This effort is streamlined by, in the case of one of my recent builds, combining three scooters into one and then repurposing the spares for the pig pile that makes future awesomeness. Your engine building skillset and thoroughness is legacy level and I appreciate the "eyes" you have that i can see through for when I run into conundrums when splitting cases. Truly big brain tactics when you puzzle out challenges in the field of going where no one has gone before. I just completed and fired my first RC1 build and I don't have to tell you the feeling of that first catch you hear. Used your build diary relentlessly so the path was not as daunting to walk. Thanks man, you have definitely made a scoot empire that is an Eden for both 2T and 4T players. You ever get into Richmond, VA shout out for the grand tour of the fun shit.

[90GTVert]

The owner of that engine sent me this pic last night :




That’s up at the cylinder base that he cut for the larger jug, not where I cut for the crank. Not saying it’s anyone’s fault… I’m just glad it’s not beside my work. He only brought 2 bolts with him when I put the crank in, so he was installing the rest.

He said he barely started the bolt and it broke off.

His friend that welded aluminum parts for him before is busy and he says he doesn’t even want to bother him anymore. He asked if I could help him find a welder on marketplace that could do that job. I told him from what I recall of the guys that have welded aluminum and cases on the forum it should be 220V and AC capable TIG. Sent a link to an Eastwood listed near him for $500, but warned him that it sounds like a learning process even if you can TIG steel already.

I said the bad parts are that it’s a sealing surface that has to be flat for both the cylinder and the case halves to seal… and the engine has to come apart or at least someone would weld both cases together trying to fix it. He says it doesn’t need to come apart. Just separate a very little bit and weld. I told him a pro welder may be the way, but they will surely want it apart.

I said another problem is gonna be threads, but he says a longer bolt should work.

He sent me a pic of a Chinese TIG on eBay for ~$250 sometime after I went to bed last night. Doesn’t know if that will work. I don’t know enough about it. Looks like it could to me, but I never got into checking out aluminum TIG because I never took the first step for me which would be 220 in the garage.

[190mech]

The welder appears to handle AC tig, he will need a bottle of pure argon, hose and regulator, around another $300.
Then the helmet, rods and skill to tackle that job. Lots of those die cast cases are tough to weld due to the crap alloys they use..Hope it goes well!!

[aeroxbud]

Yeah it's going to be tough to weld I think. I know it's a gamble welding motocross cases which have been exposed to oil and gas. And they are far and away better quality aluminium than scooters.
It seems like no matter how clean you get them. You can never get rid of all the impurities.

[oldgeek]

I would JB weld that in a heartbeat! Drill and tap hole deeper, drill a couple small holes in bolt for epoxy to stick to, dam it up with tape and file it down after it cures.

To me it looks like the wrong bolt was used and it bottomed out.

I wish him luck.

[90GTVert]

Jun 9, 2024 17:58:17 GMT -5 oldgeek said:

I would JB weld that in a heartbeat!

That's what I said. He said that won't work and it needs welding. He doesn't want to pull the cases apart. To me, at that rate, the only option is an epoxy. You're gonna join the case halves with whatever you do at that point. At least JB would be a lot easier to get apart someday if needed and you aren't putting all of that heat into everything and it would be easier to smooth out to let it have a chance of sealing at the base.



Thanks for the replies.

[90GTVert]

He had a pro weld it. Welded it all together. Hope it all works.





He went to NYC yesterday and bought a whole Dio for $400. Took the engine out and brought it to me today and it’s now another big stroker.





One of the exhaust mount tabs is broken off, but he’s gonna get the welder to fix that.

[oldgeek]

Looks good from here!
I recently picked up a basket Elite, Oldskool let me have it because he moved away. It's been setting outside in the weather for quite a while, no jug, crank stuck, looks pretty bad off. I pulled the motor off today and put the frame in the scrap pile. I will pull the motor apart and see if it is trashed beyond repair. I have no need for it so you or your friend can have it if you would like it.
Oldskool also gave me a nonrunning Kymco ZX, I dont need another scooter but could never turn a free ZX down LOL! Oldskool also gave me a 125cc LC cylinder kit with crank, much like the one you posted a while back. When I get another set of cases ready I may give it a try.

[aeroxbud]

I just don't like the idea of boring into the mounting bolt holes. But then I'm not a Honda guy.
It's not so bad on the Piaggio engines where you flow the cases. It's possible to go through the bottom of the stud hole. But it doesn't affect the strength of the stud thread. And a little JB weld fixes it.

[90GTVert]

Jun 16, 2024 4:45:18 GMT -5 aeroxbud said:

I just don't like the idea of boring into the mounting bolt holes. But then I'm not a Honda guy.
It's not so bad on the Piaggio engines where you flow the cases. It's possible to go through the bottom of the stud hole. But it doesn't affect the strength of the stud thread. And a little JB weld fixes it.

Same. I told him it's a little scary to me chopping this thing till a chunk of the bolt passages are gone. Even weirder is that one side of the cases has a lot of meat and the other side has just a thin area left to seal. The 3 sets of cases that I've seen him bring over were all that way. When you put them together, the sides don't look aligned because of the thickness mismatch. Did they make the thicker half and then the bean counters said, we can save money if we make the next side thinner? Obviously these were not intended for 52mm stroke, but I'm used to seeing both case halves look similar.

I've told him multiple times now that he should consider Minarelli or Piaggio based builds in the future. He said now he's thinking about taking the aftermarket stock stroke crank out of the Jog engine that I just put in recently and having me make it a 90. I said just build a 70. Get quality stuff and they can run hard. Of course that's a different road too, because for it to run hard it's no longer the more forgiving street stuff and I think that would be quite an experience for him. I just do the bottom end crank clearance and assembly. He ports the cases, cuts for the jug to fit, installs the cylinder and tunes and such and already struggles to have his 2Ts or 4Ts in reliable tune to be able to ride them without them shutting down, presumed to be from overheating.

[90GTVert]

Anyone have a reasonably priced source for AF18 seals for large (20mm) cranks? Looks like it should be 20x25.5. I found a site listing conversion seals for $35, prob plus shipping. He’s not gonna pay that. I’m thinking if all else fails, maybe a 20x25 seal with sealant on the outer edges or a 20x26 if it will go in without deforming. I’d prob just buy the conversion seals, but I’ve also seen plenty of leaks from new seals that fit as intended when leak testing.

[oldgeek]

Jun 16, 2024 10:13:57 GMT -5 90GTVert said:

Anyone have a reasonably priced source for AF18 seals for large (20mm) cranks? Looks like it should be 20x25.5. I found a site listing conversion seals for $35, prob plus shipping. He’s not gonna pay that. I’m thinking if all else fails, maybe a 20x25 seal with sealant on the outer edges or a 20x26 if it will go in without deforming. I’d prob just buy the conversion seals, but I’ve also seen plenty of leaks from new seals that fit as intended when leak testing.

You sure of those dimensions? that's like an O ring