First time adding displacement.

[69ST]

What you wrote in post #200 seems like the issue. I hadn't realized that you were using the cheapie crank in this one; that explains the weird CW diameter. And, no, I would not suggest changing-over to 12v cases. If there's a crank-to-oil pump-drive interference issue, the only viable solution is machining the drive shaft. The operative word being "if".

IMO, cutting-down a cylinder, to adjust deck height, is second only to shaving a cylinder head to adjust static CR, in terms of unintended problems. Unless a custom timing chain is possible, IDK that there is a workable method for taking up the slack. Cam timing may also be affected.

I have a feeling that by the time you've reached the bottom of this rabbit hole, that inexpensive crank may end up costing more than some others. Don't get me wrong, at the price it's tempting...very tempting; I've wondered about this one myself. The point, if there is one, is that the "best" way to go would be with a piston that fits...i.e. proper deck height and compatible with the head. If there's no such piston available, off-the-shelf, then it boils down to having one machined to fit...if that is possible, or sourcing a custom piston...which, presumably, would erase any cost savings.

Believe me, I'm not laughing at you. I've had plenty of these "adventures", since I started tinkering with engines, in another century. It only hurts for a while and the less you have invested, the quicker the stinging sensation goes away. This is engine builder/tuner school and some of the multiple-choice questions have no right answers. :22:

 

[kirrbby]

Terry gave me the take off cylinder and piston for this motor and told me to send him a pic of the deck height. We went from there. DRATV will sell a kind of kit with this crank. And I have one of those. But I think I ordered a 51mm cylinder and piston and sent them a question, will this setup work with the crank? The reply was basically, yes it should work. Let me know how it works out.

I should mock up that cylinder kit and check the deck height on it.

I could get a little more distance out of the tensioner if I cut a little out of the arm, or case I spose, but...

I also have a stock TRX 90 cyl piston that I could mock up. This is all good stuff for me, just bad timing. I need to take a little time with all of this before I put the motor back together. Maybe good midnight tinkerin material.
I think every other cylinder and piston I have in 69mm high is for a big dome head, the head on this motor is new dome (93 CT70). I'd need to clean up another head if I want to run a cyl kit that I have on hand. And if I want to use the 51mm, I'd need a oil cooler, exhaust, etc

 

[Adam-NLV]

Excellent thread Kirb. I'm only on page 7 but it's going down the same alley as my tb 88 & stroker build.

Just wanted to subscribe, oh yeah my 88 kit looks exactly the same as yours & the piston matches too.
I was looking through my kit and found out that Tbolt included a Cam sprocket w/Dowel 28T.

Hope to make progress on my build this weekend.

View attachment 26456

 

[kirrbby]

PARTS TO MAKE A 51MM/109CC SUPER LONG ROD STROKER<p> FOR_A_CDI MODEL_50_OR_70

 

[kirrbby]

I did a quick comparison of the piston from my motor and a stock TRX 90 piston. TRX on the right in my pic. It looks like the TRX piston would work without cutting down the cylinder. It's about a mm or so taller to the outer edge with a slightly flatter dome. I think I'll try the TRX cyl and piston with the same head. I think it'll work just dandy. The cylinder needs honed, blasted, and painted. There's also a extra hole that will need to be plugged up.

Don't worry, the cylinder in the pic is not the one I'll be using.

 

[69ST]

"What, me worry?":crazy:

The tall-dome pistons required with a short-stroke + hemispherical are needed to get decent compression; but, the shape impedes flame propagation and breathing. A long-rod, long(er-than-stock) stroke and fla(ter) piston should be pretty efficient and work well at high rpm. Honda has gotten good results from the long-rod/long stroke, undersquare configuration, with the Nice & Grom motors. You cannot really use a dished piston with your motor. You'd end up with 6:1 static CR. However, the smooth/low-profile dome ought to come close enough and give you enough compression to make some real hp/cubic inch.

Methinks this motor will run pretty well, with a fairly rev-happy character.

 

[kirrbby]

Well I'm a bit of a hacker at heart. A old carpenter who know 9 different ways to "fix" most anything. But I'm tryin to be better. The old Kirby would have just put this motor back together using the the best of 3 used cam chains that I have here, and the best of 2 used trx90 cyl/pistons. Scrubbed the cylinder with some Emory cloth and with a couple dabs of rtv on the old gaskets, I'd have been back in business. But, here's what's happenin. I ordered rings,4 cheapie base gaskets, a did cam chain, and a 1mm thick alloy gasket, ($60 shipped) from DRATV. Which I got today. The trx90 piston sticks up a bit high when mocked up without the gasket. So I popped on the thick metal base gasket. Since, I started thinkin. (a little late, but) the trx90 crank has a 49.5mm stroke, the crank I have has a 51mm stroke. 1.5 mm difference. I should have bought the 1.5 mm version of the alloy base gasket instead of the 1mm

So then I had the cylinder in my truck to take it to be honed. It looks really good, just a little too smooth in the bore. My 1st choice would be to take it 20 minutes North of my workplace to my friend Jerry (Irondog), then be patient cause he's a busy guy. My 2nd choice is to take it 5 minutes North, to the Honda shop on my lunch break, then pick it up after work. So I opted for quick and easy, went to the Honda shop where they told me that they now send all their machine work out to Irondog. lol. The world seems to keep gettin smaller. I didn't leave the cylinder. I'm back to scrubbin it with some sandpaper and runnin it. I'll add a paper gasket to each side of the metal gasket and check the deck height. Might have to order a thicker one. I'll blast my cylinder at work tomorrow if possible, and paint it. This motor was meant to be a fun experiment and learning experience. So far it has been. And the electrical, (12v no battery) is still to come.

 

[OLD CT]

Sounds like a 2 1/8 inch 400 grit flexhone would be a great addition to your tool box.

Ya wanna put some oil in the bore, before you hone. It doesn't take long to hone a cyl. Maybe 5 or 6 up and down motions,half in half out keeping it in the bore.

 

[kirrbby]

Each time I've looked into buying a hone, I've found those flexhones everywhere. It seemed too...unscientific, to be a good choice. I spose better than a piece of sandpaper on my longest finger tho. You've already answered any other questions that I may have had. I'll be buying myself one OLD CT. Thanks for the tip.

2 1 8" Engine Cylinder Flexhone Flex Hone Hone 400 Grit | eBay

 

[OLD CT]

Now you have good use for that rusty jug,practice!

 

[69ST]

I think you're viewing this from more of a woodworking perspective. Honing has been scienced-out over the decades, to the point where race engines and a lot of OEM motors can be caned pretty hard, right from the get-go. With few exceptions, that is a world apart from our little engines. The old dingleberry hone is one old school item that's not going away...because it works.

The amount of material removed, whether finish-honing, or just de-glazing a cylinder is minuscule, as in "not measurable". All you're doing is scratching the surface, literally, in a highly controlled manner - to both hold more oil and accelerate wear, for a very short period of time...seconds...just enough for the rings to make full contact. Crude?...perhaps. But, how does it compare to a couple of fingers wrapped in emery cloth?:21:

FWIW, back in the old days I knew a number of guys who used to overbore go kart & minibike engines with this type of hone. The "real pros" :butcher:started with a fixed-stone type, in a drill press, for the bulk of the material removal. The process took what seemed like f-o-r-e-v-e-r, even a 0.005" overbore. Some of them seemed to get decent results. Personally, I found the practice cringe-worthy even in 1970 and what I saw, on the track, was more than enough to confirm my suspicions.

 

[kirrbby]

Well I just ordered this one.
1 7 8" Engine Cylinder Flexhone Flex Hone Hone 320 Grit | eBay

The cylinder I'm working on is 47mm and 320 grit seemed close enough. I'll likely end up with at least 3 different sizes of these. 1⅞-2 & 2⅛"

 

[kirrbby]

I made a cover for... whatever this extra hole in the cylinder is for. I used the tube to make the pattern, but I should have used the port on the jug instead. The cover would have matched much better that way. No biggie to me, but kinda dumb is all.

I also mocked up the rusty cylinder/piston with the 1mm thick metal gasket to check the deck height. The cylinder still had a gasket on it, and with the metal gasket the piston comes up just about right.
I haven't painted the cylinder yet.
My hone should be here Saturday.

 

[kirrbby]

Boy I tell ya. It seems that I like to learn my lessons the HARD way. Long story short, my motor now has a new serial number and, I know how to use a torque wrench, and how NOT to try removing a broken cylinder stud.

On a good note, my motor is very near completion.
re-recompletion. Another half hours work plus a hour to get it back in the bike. Then I can start to break it in, again. :-/

 

[69ST]

Not trying to embarrass you, wadjya break?:7:

 

[kirrbby]

I snapped the upper left side stud. The cylinder and head stud. One of the ones with the locating dowels. Left just the threads of the stud in the engine case. Then I tried to drill it out with a somewhat dull left hand drill bit. Ya, bad move. Scrapped the left side case.

Had the whole motor together and was just torquing it down. Grabbed my small torque wrench and it was already set to 10 ft lbs. Started tightening in a criss cross... Snap. The knurled nut in the bottom of the handle of the wrench was backed out. Loose. So the wrench didn't pop when i t was supposed to. I should have (and kinda did) recognize that somethin was wrong. I'm lucky I didn't damage the right side case too.

Motor's back together now. All that's left is to notch the new left side case for the CDI pickup and recheck the valve lash.

Ya, I'm a little embarassed. But I don't mind admitting to it.

 

[OLD CT]

How did the hone work out? Are you a master honer yet?

 

[kirrbby]

Hone worked great. I thought maybe it could be a little coarser. Maybe go to 150 grit or so. Not sure if I did it right but I was happy with the result. Deglazed the bore. That's what I was after.

 

[OLD CT]

That sucks about that stud. I wonder if that can still be fixed,now at least there is no rush. And if it can, you will have it for the bike when its time for a freshen up. Nah, 320 is course enough, and now you have another handy CT70 specific tool in your arsenal. O.K now I see it's cocked in there. Ugh.

 

[kirrbby]

The stud went in straight. I just overtightened it, and snapped it. Then, I tried drilling it out. My bit slipped off the stud and dug into the aluminum case alongside the stud. Then I tried a bigger bit for a few seconds before throwing in the towel. I have lots of engines and cases. I grabbed the handiest one. A k2 Z50 left side. Cleaned it up and made the swap. The damaged part could be salvaged I'm sure. I just don't think it's worth the effort. Not when they are so cheap and plentiful.

The hone was a very good purchase. I'll be getting another for bigger bores. Probably the 2⅛" you recommended.