Ace 90 cylinder on a ace 100

[Ajf]

Is the ace 90 cylinder the same as an ace 100 but with a smaller bore? I have an e code ace 100 that needs a new cylinder and a friend says they have an ace 90 cylinder I can have. I was wondering if I could bore it to accept the ace 100 piston. Thanks in advance for any help.

[hodakaguy]

Is the ace 90 cylinder the same as an ace 100 but with a smaller bore? I have an e code ace 100 that needs a new cylinder and a friend says they have an ace 90 cylinder I can have. I was wondering if I could bore it to accept the ace 100 piston. Thanks in advance for any help.

The parts list shows they are the same (Pt# 902501A). If they are not, blame the parts list.

[Zyx]

The Ace 90 had a bore of 48mm and a stroke of 50mm. The Ace 100 had a square bore and stroke at 50mm. Also the intake, exhaust, and transfer port timing are not the same. I would guess that, assuming the cylinder studs are spaced the same and the same length, the cylinders would swap back and forth, but would need appropriate pistons and carburetors to function. I have never tried it, but I don't doubt that someone out there has. As for boring a 48mm cylinder to accept a 50mm piston, I wouldn't think so even if there is enough steel in the sleeve to allow it. Or, even if you did this, you would have to port the Ace 90 cylinder to match Ace 100 specs if you wanted it to make reasonable power, unless you want to build a trials bike that makes more torque than top end hp.

Someone has likely already paved this road and can speak to the pros and cons.

[Zyx]

"The parts list shows they are the same (Pt# 902501A). If they are not, blame the parts list."


Cylinder part numbers are different. 902505 for the 90, 922505 for the 100.

But I guess it depends on whether the question is about cylinders or heads. The question started one way and ended another. Heads are probably the same.

[Ajf]

I'm sorry the question is about cylinders. I couldn't figure out how to edit the title.

[Zyx]

No problem. About the cylinder, then, only if you really want to convert your bike to 90cc would I use a 90 cylinder, and I would have to verify that the piston pins are the same in both the 90 and 100 to know if you could use the 100 crankshaft with a 90 top end. Even if the stroke is the same, there could be differences. Checking the parts list for 90 and 100 rods might offer a clue. If they are the same part number, no problem, but if different you would have to know how they differ. Some used a pin bushing and some a bearing I believe, so compatibility is not guaranteed.

Is there a reason you can't rebuild the cylinder you have? You say it needs a new cylinder, but what causes you to make that conclusion? If it is destroyed, okay. But if just seized up or rusty, I would see if it can't be rebuilt. Even if it is bored to the max allowed, it could be recoated with a nickel based coating and reused. I want to say the process is called Nikoseal, but I could be spelling it wrong.

[Zyx]

Spelled it wrong. It is Nikasil. A nickel based electroplating process that many have used to salvage vintage cylinders.

[taber hodaka]

Ajf you have a 100cc engine and wonder if you can put a 90cc cylinder on it?? Yes you can bore it to 100cc. It is a go no problems. Just round the ports as is required after any bore. It will run fine, great. Use the 100cc head. ----------Clarence

[Zyx]

Port specs Ace 90:

Exhaust duration: 159* 56'
Transfer duration: 128* 20'
Intake duration: 122* 20'

Port specs Ace 100:

Exhaust duration: 164* 46'
Transfer duration: 128* 20'
Intake duration: 131* 28'

While transfer porting is the same between the two, intake and exhaust are not, with intake timing being the biggest difference. The Ace 100 had hotter porting than the Ace 90. The 90cc cylinder will apparently run as a 100 with 90cc porting, but it will be detuned from standard 100cc porting. As I mentioned, I would expect a 100 with 90 porting to make less power and more torque than standard, which is fine for trials, putting around, and general trail riding. Using the 100 head will probably bump up compression slightly but not much. In the end you will have more power than a 90 but a bit less than a 100, everything else equal.

Since you already have a 100 cylinder, you can compare port heights between the two, and if so inclined, you can easily match porting on the 90 cylinder with a Dremel tool. It won't take much. I found porting to be addictive back in the 70's, and ended up doing a reed valve conversion, and porting to Super Rat specs on my 100B, stuffed the crank, and piddled with the transfer ports, but then changed to a Webco 125 conversion after the first year of racing, and never looked back. These days, the original 100B bike is just about to be a Super Combat 125 conversion. Almost done. There is no such thing as enough power.

If Clarence says it will work, it will.

[Ajf]

This is a great forum. Lots of good info and good people. I have 2 hodaka ace 100 engines I'm rebuilding (an e code and a p code). I recently visited roger lippiatt and traded my cylinder that needed rebored and honed for one that was already done with a new piston in it. My other cylinder I just noticed has a crack at the bottom part of the cylinder that slides into the engine. I'm not sure if it can be fixed so I was looking for another cylinder and ran across the ace 90 cylinder and was told they were the same but wasn't sure. By the way if anyone gets the chance to visit roger go, he is so full of knowledge, stories and he has so many cool and rare hodakas, a couple of bonanza mini bikes and lots of other cool stuff including a hodaka trike.