Filtering by Category: engine


After getting word from Harold that the cylinder would need to be bored .50mm over (or the 2nd over) I started sourcing a piston and a ring/rings.

Yamaha switched to a reed valve induction system in 72 which made more power and was more efficient presumably (they've been using reeds ever since). Pistons for those engines are easy to find…like order-them-in-a-catalog easy.

DT1 pistons…not hard to find, but they’re the order-them--on-ebay kind of not hard.

Found a decent deal after little to no searching; a DT1MX Piston. When I bought it, I knew there is a different piston ring configuration than the DT1E (what I have)

I learned after getting the piston and looking at it that the skirt is also much shorter (this will affect port timing) and that the piston is a good few ounces heavier than the old DT1 piston.

Though thinking on it now, the old piston was gouged, had another ring grove, and lived a hard life in its latter years. It’ll find its way to a book shelf or a desk to lead a less stressful life…

There’s something really reassuring about going to a place of business that’s named after a man and actually talking to that man. This was the case at Harold’s Machine Shop.  It was a 2 man operation in Richmond, Tx as best I could tell. I think is comrade was named Donnie. I gave him the piston and ring so he could do the finish work and I picked up the cylinder the next day.

Steel liner needs to be filed to smooth the transition between ports/cylinder wall. 

Steel liner needs to be filed to smooth the transition between ports/cylinder wall. 

I’m a little sad that it didn’t come back hot tanked or cleaned, but for $64 I have no room for complaint.

I was unable to find what the proper ring gap should be. I feel like the gap might be large, but can’t say for certain without the data. We’ll see how it runs…

Somewhere in the time before, after, or while the cylinder was in the shop, I slowly collected my pieces from USPS. A tachometer drive gear, a shift shaft washer, a tiny oil pressure spring and a 5/64ths diameter ball bearing. A rubber “oil pipe holder” and a grommet for stator wires.

I’m happy to say that it was a day ago when I put the clutch side engine cover on with black oxide allen screws and plan to never open it again. (But I’m a realist. I know it’ll be open again…)

Gear on bottom left is Kickstarter. Didn't look right. Should have known...

Gear on bottom left is Kickstarter. Didn't look right. Should have known...

How we fix torn gaskets. 

How we fix torn gaskets. 

The gasket kits for these engines, or maybe just the ones I’ve gotten (because this happened with the DT2) are some odd sort of deformed. Not enough to matter from a functional standpoint, but just enough to put weird stress on the gasket at certain bends.

I put the kickstarter shaft in (thinking that it was all too easy) and buttoned the whole case up. After kicking it a few times, I noticed the kick starter shaft was installed wrong. Goody. So off the side over comes, I re-set the kick starter shaft (not rocket science, but a return spring has to catch on a certain knob) and upon trying to put the cover back on…tore the gasket. I’m thinking it’s nothing Motoseal can’t fix.

I was going to just stick the autolube system on (oil pump) and let it ride….but it kept me awake at night not knowing if it was full of sludge or solidified castor oil or what. So I took it apart….

Last time I took one apart (DT2) I ruined it.

2 Stroke oil pump. No need to premix as long as you have faith...

2 Stroke oil pump. No need to premix as long as you have faith...

These bikes (all bike, really) have road maps..exploded part diagrams for every little system showing what part goes where, what part number it is and how it interacts with other things around it. It’s like a mechanical, 3d paint-by-number.

Part 23 does not exist on earth. Also note #12- a screw. Behind those 4 screws is the insanity.

Part 23 does not exist on earth. Also note #12- a screw. Behind those 4 screws is the insanity.

The oil pump is an exception. There’s no diagram showing what’s in the pump. It’s some gears, microscopic (honestly, damn near…) springs, some seals, and a crazy array of different sized washers of different thickness that are of critical importance.

I ended up being glad I took it apart because there was some crap in there…but it was a very painstaking time. SO much so that I took 0 pictures. As a plus, though…I lost the little spring and the directional gear that ratchets on them. BUT I found the springs. And managed to get the gear back on. Doesn’t sound hard…but it was an amazing feat. I’d read from a few people “If the gear comes off (off the spring loaded pins) throw the pump away and find another one.”

Feel pretty good it’ll pump oil…I modified the lower banjo bolt since they don’t make and it’s impossible to find a spring that goes in it. Drilled the hollow bolt out a tiny bit and was able to get a later model spring (from a 76 DT250 oil pump) to fit. No idea if it’ll operate correctly so careful testing will be done before firing.

Next steps- Black letter the “YAMAHA” on both sides

Port and polish the cylinder, polish the head.  (tools are in the mail. Doing it by hand got old fast.)

Powder coat the cylinder and head

Bolt it together.

The end? Don’t know what to do after that…

Sealing it up. 

Sealing it up. 

I do feel pretty good about this engine though. As far as tolerances, parts, function, and the fact that literally no stone (or bearing) has gone unturned.

And in the end, it’ll amount to a loss of money because no one will buy it, I don’t have anywhere to ride it, the “bill of sale” is some scribbles in red ink from a 14 year old, and I don’t really know what to do with it…

But it sure is a lot of fun building it.

Should probably take up fly fishing instead. 

Portal 2

Some weeks ago I started porting the cylinder on the DT1. The last time I ported a motorcycle cylinder (head) I was maybe 16 and the bike was a Honda Z50. (it was an overhead cam engine, so the intake and exhaust ports were on the actual cylinder head. On two strokes, the ports are built in to the cylinder itself. The 2 stroke cylinder head is nothing more than an aluminum chunk with a combustion chamber, nothing else) I also had plans to supercharge that bike with a Coleman battery powered air pump and PVC pipe adapters.

Porting is the enlarging, smoothing, and streamlining of intake and exhaust ports. Sometimes it’s called porting and polishing (polishing is what it sounds like) the idea is that smoother, hand shaped ports allow air flow to move in greater volumes with less restrictions. The result- more power. Or, if you’re from East Texas, more “pahhrR.”

I’ve learned most of everything mechanical through reading, studying, looking at pictures and most of all by actually doing it and messing up. But my philosophy on life has changed, and that’s transferred over in my approach to this porting project.  My philosophy now is take baby steps forward instead of a huge leap. And as much as possible…don’t overdo things.

Some grinding done to the xfer ports before I got there

Some grinding done to the xfer ports before I got there

So I started with the transfer ports. Big chance to help smooth air flow, small(er) chance to really ruin things. When I got the cylinder, I could have sworn something had been done to the head. I had high hopes that it was a rare performance part from Yamaha, but having no way to substantiate that, I’m 98% sure it’s a factory, run of the mill cylinder. Most likely the 14 year old kid who had the bike before me, or the owner before that, did some work to the transfer ports. It's cool to think that some old guy back in the 70s did this to hop up his bike. You can see the color difference between the regular cast material and the material that was ground down years ago. Given the fact that the inside of the engine was so clean and the bike in general looks like it was never used, (wheel bearings perfect, hubs still showing clean grease, transmission gears showing almost 0 wear) I think this is old work, not done by the kid I bought it from.

2 strokes don’t use valves and camshafts to control air/fuel and exhaust. They use “ports” which are really just holes in the cylinder that allow gasses to flow through at certain times.

The 2 stroke relies on the crankcase to hold the air/fuel/oil mixture, relies on the transfer ports to get this mixture in to the cylinder, and relies on the exhaust port to get the spent gasses out of the cylinder.

Stock transfer ports on a GYT Cylinder (stolen from Vallyrider and his rebuild thread,

Stock transfer ports on a GYT Cylinder (stolen from Vallyrider and his rebuild thread,

In the photo to the right you can see a thin dark "stained" area for lack of a better work on the flat cylinder surface.  To contextualize, the cylinder is upside down in this pic. When installed on the motor, this surface is in contact with the crankcase. This dark stained area over hangs in to the crank case, disrupting and obstructing a portion of the flow. This part is easily ground away to port match the cylinder to the cases. 

Why port/case matching helps. The person before me filed down the center divider to smooth air flow. 

Why port/case matching helps. The person before me filed down the center divider to smooth air flow. 

If you look closely in the center of the picture where the case (grey silver color) comes in contact with the port (the two black/brown open holes) you can see the difference in surfaces. 

If you look closely in the center of the picture where the case (grey silver color) comes in contact with the port (the two black/brown open holes) you can see the difference in surfaces. 

Close up of the surface and material removed with a carbide bit to match the transfer port to the case. This will be smoothed with sand paper and then be finished. You can also see the scoring in the cylinder wall, which is why it needs to be bored. 

Close up of the surface and material removed with a carbide bit to match the transfer port to the case. This will be smoothed with sand paper and then be finished. You can also see the scoring in the cylinder wall, which is why it needs to be bored. 

The engine manages to do all this with nothing but a piston, the changes the piston creates in air pressure, and it’s path of travel up and down the cylinder. Piston Port induction.  The earliest, simplest, (most inefficient) form of 2 stroke awesomeness. There’s some good info online about how they work, but here’s a good animation from


So porting…why not make the port as big as possible, polish it mirror smooth, and profit?

That’s pretty much the plan on 4 stroke engines (pretty much everything today) with the caveat being that if you port too much, the port walls are too thin. Behind the port walls of almost every 4 stroke engine- water jackets that transport coolant. If the ported wall is too thin you can get a leak, and that’s all sorts of bad news.

For 2 strokes…since the efficiency of the engine relies solely on the volume of air the piston is able to move in 1 stroke, if you make the ports too large, the gasses will not move with adequate velocity.  The whole deal with two stroke porting is balancing velocity and volume.  The other mess that comes in to play is port “timing,” or when ports open in relation to one another and for how many degrees of the rotation of the crankshaft. There are some good DT1 port maps out there based on the DT1MX, which came with a higher performance cylinder. Doing that level of porting requires a lot of time, skill, and faith. All of which I have…but I have it in baby steps.

How it looked when it was first opened...

How it looked when it was first opened...

I was going to buy a new cylinder for this engine anyway. The kid before me ran this thing without oil (he tried…he spliced the oil line in 3 places with 3 different kinds of tubing, and he did put 10w30 in the oil tank (not the right oil, kid…)) and the piston did some damage to the cylinder wall. I broke out the dremel to begin smoothing out the transfer ports from the work that was done before. I feel like I did well. I need to do hand sanding, but I didn’t take much off and smoothed transitions where possible.

After looking at prices of cylinders on ebay (and their terrible condition) I decided to seek out a machine shop around Houston that can do the work. Harold’s machine came up as the place from a couple of recommendations, and as of today that is where the cylinder sits.

I’ll need to get a piston before he can finish the work, so there is that.  But once done, I can finish the ports by hand, powder coat, and put it all together.

It has dawned on me that I have nowhere to start this thing around here, living in a small apartment. It may have to be transported to San Antonio in pieces and assembled there. 


lot of small things going on and moving forward here.

It started a couple of weeks ago when I decided to drop in the bearings. They had been sitting in the freezer for a long while and something motivated me to finally start putting the engine back together.


Frost on the inner race

Frost on the inner race

In the oven the cases went. Somewhere around 300 degrees for a few minutes.  After the cases were hot, they were taken out and the frozen bearings dropped right in to their races. There was one exception, a needle roller bearing on the small end of the transmission. It took some mechanical persuasion. All of the others literally dropped right in. As the freezing metal quickly warmed in its hot new home, the bearings expanded to their tolerance and stayed in place.

Before being sent off. 

Before being sent off. 

The rebuilt crank came next. I stared with the shim side (gear side, clutch side, right side, whatever…) and pressed it in to the case as best I could using a plastic mallet.

The transmission came out of its foil packet (where I’d placed it some 7 months earlier) and I dropped it in to its place. With a little tweaking and coordination, I was able to get both gear shafts and the shift forks all lined up and in place. This isn’t particularly hard, but it takes some synchronous movement of parts.

Back in college I remember taking apart an old GT80 for the hell of it. When it came to opening the cases…I was blown away. So much stuff. So many parts, so many washers, shims, forks, bearings…I gave up, sold the project.

Rebuilt. New thrust washers and lower bearing (and upper bearing)

Rebuilt. New thrust washers and lower bearing (and upper bearing)

After doing 2 of these, they really aren’t that complex or scary. Intimidating they may be..but parts diagrams are helpful and every part is engineered with a purpose. There’s a 2 part retainer and a shim that goes on the transmission. Without those 3 little metal parts, the whole trans can be disassembled down to gears, clips, spacers, and shafts.  These tiny parts hold the bronze gear in place.

By far the best advice I ever read was to just put the whole thing in foil, though. It keeps the small parts from falling off and walking away. It preserves everything from accidental bumps, moves, falls. And there is not really anything on the transmission to be serviced (unless you have to rebuild/replace it like I did on the DT2) so it’s easy to set it aside.



Crank is in, trans is in…next step is bonding the two cases with a sealant/adhesive. In japan, they used Yamabond 4 or 6 or some number. The numbers are different formulas. I’ve used a product called motoseal that smells like plastic model adhesive (a wonderful smell) and works well. It’s a semi-drying viscous grey matter that is very very sticky.  After running a bead on the sealing surfaces of the two cases, it was time to squeeze them back together.

I’ve taken apart and reassembled motorcycle engines many times in the past without the right tools, and it always leads to serious damage. One of the better investments I’ve made- A case splitter and a crank puller. The crank puller screws on to the magneto side of the crank and pulls the crankshaft on to the case. This process was somewhat hard on the DT2. I’d tighten the tool and pull the crank on and then tap the rear of the case to make sure the transmission drive shaft was coming through the case as well. The DT1 went together with ease.  New allen cap screws were used to cinch everything together, the crank was tested for mobility and its centered-ness, and that was that.

There really isn’t a lot inside of the cases.




With the cases together, the other items can go back on. Stator and flywheel went on with no trouble. With the exception of the countershaft sprocket, there’s nothing else on that side of the engine.

The other side is where all the fun is. Clutch discs, plates, gears, shift mechanisms.

When I took everything apart, I zip tied it together. I know that probably doesn’t make sense, so here’s and example-

The gear that goes on the crankshaft has a rubber o ring, the gear, a washer, and then the nut. My biggest problem when putting these things back together is remembering the order of things.

Clutch discs in background ziptied, clutch baskets/bearings in front

Clutch discs in background ziptied, clutch baskets/bearings in front

The clutch basket- there’s a spacer, a washer, a bearing, a washer, a race that goes through all of those, an outer basket, inner basket, and then the clutch discs/plates.

When anything of multiple parts came off (and everything has spacers, washers, circlips, etc) I zip tied them together in the order they came off.

This made things 1000% easier when it came time to put it back together 7 months later.

All of the small parts went in zip lock bags and grouped by function. All the clutch hardware went together, all the shift hardware, etc. I had a scare when I saw a small part in a bag and had no idea what it did. I shortly found out that it went on the shift mechanism though, and that tragedy was averted.

So the crank gear and all that goes with it went on first, then the clutch bearing sequence (most complicated part of the engine, I think.) but not the clutch baskets.

You can’t get to the shift mechanism when the baskets are in place. So I hooked up the shift shaft , detent arms, and shift drum. Tachometer idler gear and its washers/clips goes on, clutch baskets go on, clutches and plates go in, clutch activation system goes  in (a ball bearing, a rod, and a little cap) and that gets bolted together.

The nylon tachometer drive gear had a catch in it when I was testing it to see how it spun. I decided to take it off and see why…and the drive gear is trashed. I’m pretty sure I did it because I don’t remember seeing it that way when I took it off, but I honestly never looked.

Stripped worm gear

Stripped worm gear

So- I need one of those from eBay.  Oil drain and shift drum detent gasket are ordered along with a washer for the shift shaft and a circlip for the oil pump drive shaft.

Other small things like oil pump seals, swing arm bushings, swing arm nut, and some other things are in the mail.

Big needs right now- Tach drive gear, shift shaft washer, oil pump circlip. Once I get those, I can put the bottom end entirely together.

Big needs in the future- Cylinder head bore, piston/rings/pin, fuel petcock, fuel tank.

That’ll make it run.

Not too far away, but I’m starting to realize that these projects are never as efficient as I think they will be.  I may need a cheaper hobby. And no one in hell is going to buy a bike with a blue engine.

One day I’ll learn.

For now…more waiting on the mail man. 

Strippers and powder

When I got home I had a package from Eastwood sitting by the door.

Stripper and powder. In a more exciting world, that would have a different connotation.

I got the old ugly blue motor parts out and put the stripper on to the hard cured powder. And I let it sit.


The stripper worked really well, and I had serious doubts since I baked the original coat of powder on thick and long (over baked, in fact, hoping the color would change…wondering what I did horribly wrong to yield such different results from the color I was expecting. This over cooking led to the separation of the powder from the base of some of the letters. Fun fact.)

I had to run to the home improvement store to get some acetone, as water wouldn’t remove the stripper/powder/slime solution that resulted from 30 minutes of sitting  on the aluminum parts.

While the purple gel sat on the parts and did its thing, I cleaned up the remaining parts in preparation of coating.

The engine cases had been “cleaned” long ago…and it took forever to do this. I tried many methods.

O.D.C. Old dirty case. 

O.D.C. Old dirty case. 

Of everything, cleaning with gasoline (which is what I did with the DT-2) was the easiest, fastest, and most effective. Things I tried that didn’t work as well-

Simple green
Pine sol
putting them in the dishwasher
putting them in the dishwasher again
Scrubbing manually with soap and water

Eventually what got them clean was a combination of all of the above over the course of a month or more. And “clean” is a relative term. Dirt and grime still clung to crevices. Yamaha uses a nuclear proof glue to bond the cases together in addition to the screws. Yama-bond, they call it. And it gets on things and doesn’t come off without slow, agonizing attention to detail

Engine cases themselves were scraped clean with a razor blade where needed, then scrubbed with a scotchbrite pad, then washed with simplegreen and #2 steel wool. Side cases were stripped with Dekote, rinsed in acetone, scrubbed with simplegreen and #2 steel wool. 

I, like many other men (probably) am guilty of getting excited, getting in a hurry, and rushing things. This admittedly was the case with the first round of powder coating. I got the color in the mail, was super excited, and wanted to see what it’d look like. If I had the RIGHT color, it would have looked fine. But seeing has how I didn’t…

I’ve been afforded the chance to go through and better prep things. So the cases and covers have been stripped, smoothed, scrubbed, cleaned, and dried. They’re ready for powder.

But I think I’ll do a test to see how the color looks before going crazy. That’s the plan for tomorrow, maybe.

The nice thing about powder coating is that it affords a really easy, all in one step to put in new bearings.

The cases are machined to accept bearings with tight tolerances, obviously. Back in the Japanese factory these bearings would have been pressed in to place with a fancy hydraulic machine with tons of force.

Most popular way to do it today, and the way I’ve done it without fail countless times- Put the bearings in the freezer for a day or more. Heat the cases in the oven (have to do this to cure the powder anyway)

Cold bearings drop right in to hot cases. Thermodynamics in action.

Bearings are in the mail, so maybe I’ll wait until they are here and knock it all out efficiently. Either way, I’ll break out the powder gun tomorrow and do a test of the 2 stage color.

First stage is laying down a powder “chrome” which is just a glossy, highly reflective silver. Once that is sprayed, baked, and cured a translucent pearl blue will go over. The base reflectivity and the slightly transparent blue color should make a nice complicated deep looking (but not deep-blue colored) result.

If it ends up being dark blue..I’m throwing the whole thing out the window. The powder is from Eastwood this time (same place as my powder coating gun, same place as the stripper) and I have full faith in them.

Results later…

Best since Day 1.