1976 Yamaha DT400 Build

[tricky]

I picked up both frames today from CMR Racing. Both are now rock solid and back to stock. Yes, I know the shocks are mounted backwards but these frames will be stripped down again anyway.

For the frame on the left, they fabricated and mounted a kickstand bracket that looks brilliant. It's a perfect replica. They also made sure the frame is true.

For the other frame, they brought back the right rear shock mount so the frame is true.

They also machined new bosses for the passenger pegs.

For both frames, they fixed the kickstand ears. On all my DT frames, the kickstand ears are bent out so the kickstand hits the ground 100 miles away from the bike. At least 2/4 of my kickstands are fixed now!

So now I'm thinking I'll vulture 2 of the shocks (from the left frame in the 1st picture, the good shocks) to complete my rolling chassis. All shocks will eventually be repainted and rebuilt so it wouldn't be a permanent thing anyway.

 

[tricky]

So I did exactly that, vultured the pair of (good looking) thermal flow shocks from the other frame. They won't be permanent but I want to mock this thing up and make sure all is well. So I also stole my good pair of rims, which has rubber that isn't actually rotting.

The kickstand works too, but it's got a little side-to-side play as the ears are bent (like I mentioned in my last post). But this one isn't too bad, the kickstand is out probably 0.5" farther than it should be on the ground. The return spring is rusty, even after I cleaned it up. I have 2 replacements, but it's a purely cosmetic issue right now so it can stay as-is. Truthfully I just hate removing and replacing return springs.

So, the list of stuff to do gets more and more detailed and difficult. I can hook up the front and rear brakes, provided my cables are OK. I can refinish the switch housings for the handlebars. I have the airbox to refinish, and I may vulture a seat from another bike too. Who knows.

I'm also pretty set on putting one of my 400 engines in this now. I am always changing my mind The other 400 engine I have matches the frame, so that one will be built up along side this one.

I can probably have these two up and running for the summer. Then I can source a 250 engine for the other frame. The last frame has almost no parts with it, but I'm thinking of building it into an early RT1 clone if that's even possible.

 

[tricky]

Foot pegs, rear brake lever, rear brake lever pivot, and two perches.

Painted (perches will be done later)

On the bike.

Turns out the rear brake torsion arm that came with this frame won't work. Someone botched it together and it doesn't clear the rear tire now. So, I'll poach one from the other extra frame I have, and I'll pick one up later. They run for only 25$ on ebay so I'm not sweating.

Once that's painted and on the bike, I can hook up the rear brake link and get that adjusted.

Today was an engine day. I spent an hour scrubbing these crank case halves in soapy water, then put them in the oven at 275 F for about 30 mins.

There are 7 bearings total in these two halves, four radial and three needle. The two radial transmission bearings fell out at the 30 minute mark by themselves. The two crank bearings took some persuasion with a hammer but did come out without any real fuss. One needle bearing came out with a punch and a few knocks.

The remaining two needle bearings are blind and I don't have a way to get them out. This gives me an excuse to buy a blind bearing puller set

The five cooperative bearings

One blind transmission bearing, still in its place

The other blind needle bearing, which is used in conjunction with the clutch. Apparently (info from Yamaha Enduro forum) this one is only use when the clutch is actuated so it's not too important.

So 5/7 ain't bad. I'll order new bearings and a blind bearing puller set. Then I'll reheat the cases and hopefully get those two needle bearings out and all new bearings in. I'm sure the real event will involve more cursing.

 

[tricky]

Yesterday I started tearing down Engine #2 (a 400 as well). A previous owner had stripped the threads on the rotor where the flywheel puller screws in, so that was a major pain to pull. Luckily its getting replaced by the PowerDynamo rotor so I didn't have to be gentle.

When I got the engine, the piston was good and stuck. Early on, I sprayed PB Blaster in there but didn't try anything else, as this engine wasn't high up on my priority list. By the time the flywheel was pulled, the piston was free, so that was easy.

Engine #1 is on the 3rd oversize, if memory is serving me correctly. Engine #2 looks like it may actually be standard! The piston is in great shape, but I forgot to take pics of the side. Oops. The piston from engine #1 was badly scored. This one looks almost new

Not my finest camera work, yea. But the cylinder looks half decent. I'll take a bore gauge to it soon and see exactly what the situation is. Maybe I can get away with a hone and some new rings???? A guy can dream...

Now comes the ugliness. The bottom end is not in good shape. A rusty paste covers the crank. The crank isn't free to rotate all the way around either, because the connecting rod gets stuck. I was planning on doing a bottom end rebuild anyway, this just cemented the plan. Engine #1 was in much better condition than this one in the bottom end.

Under the right side cover was full of a white paste. There was also some white chalky powder that came out. I'm guessing whatever this powder was worked its way into the oil and has created this paste. It looks not unlike vomit

And that's where we are at today. No doubt I'll strip this whole bugger down to the nuts and bolts. The inside of that bottom end is gross.

 

[tricky]

Continuing to strip down Engine #2

Everything removed from the right side

It seems the support where the tach worm gear sits has been welded. I assume the original casting broke and this was the solution. I'm not sure the implications of this, if I should trust someone else's aluminum welding or not.

Cases split. These ones came apart real easy. I used my Tusk crankcase splitter for the second time, no complaints.

Right side crankcase half

I used the crankcase splitter to push out the crank from the left side crankcase half. These crank bearings are totally shot. Takes quite a bit to make them rotate. I wonder why....

The crank is in a poor state. There was some fabric down near the big end. I suspect perhaps someone shoved a rag in there while working on the top end and forgot, or a piece got snagged.

The two pieces of metal sticking out, which prevent the connecting rod from rotating fully. I'm not even sure what these pieces are, perhaps pressed in there and never meant to be removed. They aren't on any parts fiche

When I get back from vacation I'll take the cranks, cylinders and pistons from both engines to a shop and see what's what. My ideal situation would be get both cranks rebuilt, and get both cylinders resleeved back to stock bore with Wiseco pistons. But, this crank is in bad shape and I'm not sure it's prognosis.

 

[tricky]

With my CT90 at the show, I can get back to the Yamaha's. When I left it last, I had one pretty well done rolling chassis.

I haven't sent the engine parts out yet, but I hopefully will this week.

Today, I pulled off 2 more rotten tires from the last two DT wheels I have. Now, I have 3 sets of wheels. One which has rubber and is on the bike, and 2 sets that need a lot of cleaning before they get new rubber.

I continued with the first thermal flow shock rebuild. I have 7 or 8 shocks that could be rebuilt, so this is #1 and I'm learning while I go.

Before cleaning:

After cleaning, with some toothbrush action but mostly ultrasonic:

Hopefully in the next few days I'll get the shock body repainted and I can start reassembling the whole thing. Then repeat. And repeat. And repeat.

 

[tricky]

Thermal flow shocks, by all accounts an aggressively mediocre rear shock for the time period. But with the lower-end modern replacements upwards of 500$ for a pair, I think I'll do what I can to get these thermal flows back in order until I can afford to upgrade.

I currently own 4 pairs of thermal flows, all in different condition. I will probably go through all 8 to replace the seals and shock fluid.

So you know what I'm talking about, I got this pair of shocks off of ebay for $40 Canadian. The left one is after my first rebuild, the one on the right was the "before" condition

First thing is a good cleaning, I used blue scotchbrite and simple green. Then the tear down. I used zip ties to compress the spring, then its possible to remove the spring retainer from the top. Having another set of hands really helps.

With the spring off:

I simply disassembled carefully, and took note of where everything was. I used an adjustable pin spanner (for changing grinder disks I think) to unscrew the cap that holds the internals

More detailed cleaning, I used my ultrasonic cleaner with more simple green

To remove the seal from the cap, I used the same method I use for bearings. I used a sleeve anchor (3/8" maybe? Or 1/2"? I can't recall), passed through the top. Then I tightened the nut to expand the sleeve anchor to really grab the inside of the seal. Then, I used a punch to drive out the sleeve anchor with the attached seals.
Here is the seal out (still stuck to the sleeve):

Original seals are tricky to find. They were something like 23 mm OD, 12 mm ID and by my measure, something like 13 mm tall. Unfortunately, I worked off of incorrect info from the web and thought they were 15 mm tall. So, I ordered a pile of 23x12x7 and 23x12x8 from AVX Seals (https://www.avxseals.com/).

So, here is me finding out the original seal is closer to 13 mm tall (the seal was slightly damaged leading to the 12.19mm)

My "7mm" seals measure around 6.9mm. So I decided to stack two of them to achieve something around 13.7-ish mm

So we are slightly over, by my measure about 0.6 mm. Not great, but hopefully it works. Unfortunately, AVX Seals only sell 7 or 8mm tall with this ID/OD combo.

With the new double seals:

Then I cleaned and painted the shock housing and spring (re-chroming the spring would be too much $$ for these shocks). I used Quick-Glo to polish the shaft. It had a couple of rough spots, but the polish helped to bring it into pretty good condition. I applied a light coat of grease. But, I think I'll have to keep an eye on the shaft to make sure it doesn't start rusting again.

And there we go, the finished product. Now, I think I will give the same treatment to my other 7 shocks.

All that's left is to fill with shock fluid (175 cc I believe) and put it on the bike and hope shock fluid doesn't spray everywhere on the first bump.

 

[Riceburner]

Some serious work done so far. Keep the pics coming.

 

[tricky]

Some serious work done so far. Keep the pics coming.

Cheers, I appreciate it!

So the sitrep right now, I stripped and painted Frame #2, and began assembly. I'd like to get both frames to the same point, so I can go forward on them together

Frame #2 in its current state is shown below. I never really planned out the colours on these two bikes, it just sort of happened based on the spray paint I have on the shelf. I do like the semi-gloss black of the frame here. For some reason, it came out glossier than the full gloss gray of the other frame (this is Krylon rust preventative enamel). I do worry I am going to end up with too much black, but we'll see where we end up. I do like how the black and silver play off of each other. I also painted the swingarm for Frame #2 black as well, but I don't have pics of that now.

A reminder of the state of Frame #1 (it's been a while since I've worked on it, besides the new levers)

So, to get Frame #2 on par with Frame #1, I need to mount the swingarm. I also need some shocks, which I began dealing with in the previous posts.

For now, I need wheels. So today, I took a go at the rear tires. Good news, I can now have the rear wheel bearings (3 of them) removed in just a few minutes. I've had a lot of luck with the sleeve anchor technique.

I have 3 sets of DT tires. The good set is mounted on Frame #1. The other 2 sets are in worse condition.

One of my spare rear wheels has an issue which I previously identified (I'm not sure if I wrote about it here). On these bikes, the sprocket is attached to the clutch hub, and that assembly is connected to the rear wheel with a snap ring. I guess a previous owner lost the snap ring, so they decided to build up the metal around it by welding in some fashion. The metal which my screwdriver is pointing to is now welded on, and fixed to the hub. The sprocket is free beneath it, but there is no way to get the sprocket off or a new one on without machining down that hatchet job. Unfortunately, for now this hub is buggered

That unfortunate find leaves me with only one rear tire available for Frame #2. Unfortunately (lots of unfortunatelies today) the rim isn't in great shape. Outwardly, it is OK and will no doubt polish up pretty good. But under the rubber is another story. The below two pictures are after I took a wire wheel to it. Some spots are far worse than others.

I don't like that condition, so this rim will likely not be long lived on the bike. However, I need a rear wheel now so this one will do in a pinch. Now I have to make it acceptable. I used a rust converter to try to stem the bleeding. It is a jelly of phosphoric acid I believe.

With most of the rust converted, I used Tremclad to try to seal it up.

Lipstick on a pig doesn't even cover me here, but it'll do for now (maybe?!). I have some new rim tape to go on after the paint dries, then I'll take my first whack at mounting rubber. Then, polishing and cleaning the outside of the rim, spokes and hub, then on the bike it goes.

Below are some pictures which show the rest of that rear wheel. It'll clean up OK, I think

The dampers are solid rubber, and all of them are still in real good condition. I am pleased with that. It's the small victories, today...

 

[Riceburner]

How brittle is the rubber on those damper blocks?

 

[tricky]

How brittle is the rubber on those damper blocks?

Still totally malleable, no signs of cracking or drying out at all. That's why I was surprised. Maybe the PO replaced them at some point

 

[GreyGhost]

canadian tire has a small sandblaster on sale for $15 this week. Sandblasting the inside of those rims would have saved you some elbow grease.

 

[tricky]

canadian tire has a small sandblaster on sale for $15 this week. Sandblasting the inside of those rims would have saved you some elbow grease.

I wish I could, but I don't have a compressor. I'd love to be able to sandblast, soda blast, paint and powder coat. I think I could take these jobs to the next level. But for now, these two bikes are just rattlecan restos

 

[tricky]

The last week or two was a freakin roller coaster in the garage. The weather started turning nice here so I started throwing all of my attention at getting frame #1 up and running, frame #2 has been put on the back burner.

I got the cranks rebuilt, and cylinders bored out and new Wiseco pistons for both engines. Frame #1 is now at 86.00mm and frame #2 is at 85.5mm. Stock bore is 85.00.

I put the crankcase halves together for frame #1, realized almost immediately I forgot the two locating dowels. Toyed for a minute with just pretending it didn't happen, then I got brave and split them again and put the dowels in. Ok... back together. Then I sheared the kickstarter return spring by being an idiot and trying to install the kickstarter backwards. Unfortunately that spring is inside the cases... so I split them again. I vultured the kickstarter return spring from bike #2 so I could get bike #1 back on the road faster.

I am dumb:

Luckily I own both a crankcase splitter and crank puller (both are Tusk)

That was the last time I had to open the cases for bike #1. I got the rest of the engine together without incident, new seals, bearings, gaskets etc. I used the gasket kit from gasket king, as well as threebond 1211 and permatex RTV in some spots.


All together, except for the PowerDynamo alternator:

I created a pressure testing kit, to test and make sure the engine is air tight (necessary for two strokes, because they work on pressure differences).


Motionpro makes a 2 stroke pressure test kit, but it would have cost me about 600$ Canadian. Too much for me to justify. So I went about making my own, following along the general direction of others online.


This is used, I believe, for testing natural gas lines. I got it on amazon for 10 bucks.

Here is the basic layout of how it will go in the intake. That gray pipe is just about a perfect fit for the rubber intake manifold, found at my local Home Depot. I brought the manifold with me and kept trying stuff until I found one that fit. It is what is known as PLUMB-EEZE poly insert plug, and it is the 1 1/2 or 1 1/4 inch size, I can't remember off the top of my head. I drilled a hole in the top and epoxied in one side of the male-male 3/4 MPT adapter. I then installed the gauge assembly with teflon tape.

For the exhaust port (~43mm diameter), a perfect fitting freeze or expansion plug found at my local Canadian Tire:

I removed the reeds for this test, but I'm not sure it's necessary.


The testing was kind of cool, while also being a pain in the ass. I pumped it up with a manual bike pump, never going past 7 psi. It fell about 1 psi every 3 seconds to start, leaking like a sieve. I sprayed the outside with Spray Nine, though you're supposed to use water and dish soap. Basically whatever will make bubbles. I saw immediately huge bubbles forming around the intake manifold and cylinder head as well as my apparatus. I fixed the teflon tape, I used permatex RTV on the intake manifold, and I used threebond 1211 on the cylinder head gasket.


The engine passed by my standards. It lost about 1psi per minute, but the only leak was on my testing apparatus where it sat in the intake boot. Cylinder base & head, crankcase, decompression valve and spark plug all had no leaks which I could find. No doubt if I fixed that leak on my test equipment it would have held pressure much much better than 1psi per minute loss.


So, in theory, the engine should be good to go. In theory.....


To start working on the chassis, I cleaned off an instrument cluster and got it mounted. Low miles!

Right now, the paint is drying on the seat pan and hinges, as well as the tool tray, brake light bracket and front engine mount plate. Once those are dry, they will get thrown on the bike, as well as the engine, and it should start looking more like a motorcycle.

 

[bocutter]

I wish I could, but I don't have a compressor. I'd love to be able to sandblast, soda blast, paint and powder coat. I think I could take these jobs to the next level. But for now, these two bikes are just rattlecan restos

I have an 80gal 7.5HP compressor, I'm guessing close to your HD and CTC ...

 

[tricky]

I have an 80gal 7.5HP compressor, I'm guessing close to your HD and CTC ...

Buying one is on my list for sure. But, as some of the pics show, garage space is a little tight right now

 

[bocutter]

canadian tire has a small sandblaster on sale for $15 this week. Sandblasting the inside of those rims would have saved you some elbow grease.

I wish I could, but I don't have a compressor. I'd love to be able to sandblast, soda blast, paint and powder coat. I think I could take these jobs to the next level. But for now, these two bikes are just rattlecan restos

I have an 80gal 7.5HP compressor, I'm guessing close to your HD and CTC ...

Buying one is on my list for sure. But, as some of the pics show, garage space is a little tight right now

I think that went right past you.

IIRC, you are at Y & Eg. I'm guessing your CTC and HD are @ Laird & Eg and Wickstead & Brentcliffe respectively. My shop is 300 metres East of that HD.

If you have room to store a small portable sandblaster cabinet ...

 

[tricky]

I think that went right past you.

IIRC, you are at Y & Eg. I'm guessing your CTC and HD are @ Laird & Eg and Wickstead & Brentcliffe respectively. My shop is 300 metres East of that HD.

If you have room to store a small portable sandblaster cabinet ...

You are correct, that sailed clean past me. I figured you meant I should go buy one from HD or CTC. I'm up in Aurora unfortunately, but thanks for the offer! That is very kind of you

A while back I got a seat cover for this bike from Sirius Consolidated. I tried putting it on and realized I am far from an upholsterer. Put a screwdriver through it at one point because I'm too hamfisted for this ****. This seat doesn't use staples, it uses metal clips on the bottom of the pan. It's not a one man job. With the help of my buddy, we got it put together and on the bike. It's got a few ripples at the back, which my pictures don't really show too well, but all in all it turned out good.

"Good enough," has been the theme regarding aesthetics for this bike. This bike is going to be used for its intended purpose, and I don't want to fall into the same trap I did with the Trail 90 - spend too much time and money on making it look good, and then be too afraid to ding it up!

I was happy to get the tank on it, and see it look more like a bike. When I got this specific frame, it was stripped and sitting beside someones shed for what looked like a long time. You couldn't buy a more incomplete bike if you tried, it was just the rusty frame itself. So seeing it come together with my spare parts has been really rewarding.

So the status, Bike #1 (above) is coming along well, the engine is in the frame, the carb is being cleaned now. The misc parts like tool tray, airbox, battery box/oil tank etc are prepared to go on the bike. So are the tail lights. I don't think I own any indicators for this bike, I'll have to get some I think. Then it's on to wiring harness and electrical!

Bike #2 is on the backburner, but with the experience I got from Bike 1 I think I can have it up and running sometime this summer.

 

[GreyGhost]

You are correct, that sailed clean past me. I figured you meant I should go buy one from HD or CTC. I'm up in Aurora unfortunately, but thanks for the offer! That is very kind of you

I'm in Aurora, you are welcome to steal air any time. Depending on what projects I have on the go you might even be able to borrow a compressor.

 

[tricky]

I'm in Aurora, you are welcome to steal air any time. Depending on what projects I have on the go you might even be able to borrow a compressor.

Sorry, I just saw this now! Thanks! That's very kind of you


I haven't been doing too much work on the bikes lately, but today I pulled the clutch cover on the DT to see why it won't go in to gear. I pulled out the clutch and shift linkage so it was just the bare shift drum head. It seems like the shift drum is fairly stuck. It's got a few degrees of free play but then it's rock solid on either end. Rotating the transmission via the rear wheel doesn't help it fall in to place either, still rock solid on either side. It's firmly stuck in some gear

I would swear up and down that while I put the cases together, the shift drum was working correctly. Maybe I missed a shim or it popped out in the final part of the case mating

It would appear I'm not much of a natural born engine builder, as I've cocked up the transmission on the CT90 and now the DT. :crybaby:

Now I have to pull the engine and split the cases (again). This time I'm gonna be sure to measure and tolerance every single goddamn thing against the manual. Nothing gets by me this time