The RD400 drag bike

[AMCQ46]

So an update on the saga….

I found a source for genuine Yamaha crank seals and got them ordered, but the hunt for std size pistons wasnt going so well.

Talking to PJ Motorcycle engineering (2 stroke rebores and cranks building experts), they advised that the only source of std size DT175 pistons they can find are from Taiwan, and they said they wouldn’t Reccomended for a race engine. All the good makes from Japan (TRK/Mitaka) and companies like Wossner only have 2nd oversize or bigger.

So that left 2 options:

1) reborn to 2nd oversize and fit new TRK pistons
2) find a source of std size pistons

I had been chasing Harry Barlow, the original engine tuner from back in the 80s, for any advice since the engine blew up, but he wasnt going to be back from Thailand till the 21st march. I have now had a long chat with him and the good news is that it turns out that he has stashed away a reasonable stock of std size pistons, but like me, he is bothered about why the engine failed in the first place (and about the other bodges in the engine like the big end pins). SO we have agreed a plan that I take my engine still in bits over to his workshop in Leicester on Tuesday 2nd and we go through it top to bottom.

It will also be a chance to look at the expansion pipes as he thinks they have been shortened, as the peak power is too far up the rev range for the crank to cope with any overrev. he thinks they would originally have been a crossover design and about 6” longer.

Only problem with that is the jetting is set up for the short pipe configuration, and I wont have a chance to dyno before Santapod

[tony.mon]

You'll just have to jet it the old-fashioned way, start rich and gradually get leaner as the engine feels keener, with plug chops after each run.

[sirch345]

Al, good to hear how you are getting on with your piston searching, and what the next step, or rather steps are going to be.
That sounds like a good ideal to get the original engine tuner to have a look over the engine, at least you'll then know if all his work is correct, or if someone else has been in there and changed something(s), fingers crossed all works out well,

Chris.

[AMCQ46]

Update from my trip to Leicester to see Harry Barlow.

It’s only 60 miles from mine so should have taken just over an hour, except for the 20 mins it took me to find his unit with google paps placing it in a building 50 yards up the road.

I Got to a place with the right house number but no signs on any of the doors, and from the outside it doesn’t look promising. I spoke to some guys having a fag at the main door and they said Harrys unit is further in the building. Inside it is like a rabbit warren of unmarked doors, but after 50 yards i see a load of scooters in the wide corridor. I open the nearest door and i guess this is the right place as it is crammed full of machines and racks of parts, a scooter on a workbench and there is a bloke welding up an expansion chamber.

So he looks over the engine and sees that the ignition side crank web has just started to move on the hollow big end pin, even though it is welded. The weld has cracked because the hollow pin shouldn’t have been used in a race engine as it cant generate the same interference fit as a solid pin. He puts the crank on v blocks and the ignition end has 0.012” runout…. Not good.

Crank is still using standard Yamaha rods and needle big end bearings, he thinks they are fragile under the power this engine should make, so when the crank is rebuilt he will fit carillo rods and updated bearings (and new solid big end pins) before balancing and welding

Then to the barrels.
there is too much clearance measured against the std size pistons, so this is why the piston skirt has failed (0.0055” when he wants .0025”)

So will need a rebore up to 2nd oversize (+.5mm) and fit modified Weisco DT200 pistons ( I am going to buy 4 sets just in case)

Next the cyl heads.
He is not sure this is his work (i knew it was done by someone up in Scotland, so he is correct) as the angle and compression ratio are not as aggressive as he would do, but he will need to machine the heads to match the piston crown angle for the new pistons so they will get reworked once the crank, pistons & barrels are built back onto the engine.


Bottom line is that there is too much work to be done between now and Sunday as he has committed work coming out his ears.

Plan is he will do the crank and rebore by the 13th, then I will build up the engine and take it back to him to measure and reprofile the heads and finish putting it together.

Then once engine is in the frame I will bring the bike back to him so he can redo the expansion pipes to the correct length and reinstate the cross-over and make sire they fit the frame and stay out of the way of my feet.

He also spotted that the stingers on the pipes are different sizes! One is 25mm ID the other is 23mm!, so they need cut of and matched!

I was looking at some of the pipes he was making for scooters and it is an art.

He has loads of flat paper templates for each section of the pipe which he uses to cut out thin steel sheets. He then rolls them into a ring or a cone, and puts 1 tack weld in to hold them together, then he then he arranges the sections in 3 dimensions to create the snake curves to work round the other bits of the bike and puts a couple of tack welds in to hold them together, till it all fits the bike… up to 30 shapes all numbered.

Then once off the bike he fully welds all the seams and then he heat treads the weld zone to reduce the risk of cracks….. proper engineering porn.


So for Sunday 7th Run What you Brung at Santapod, I just have to decide am I going on the storm or the KTM

[Duffy1964]

Sounds like he has all the solutions and you have the initial expense to get it built. That sounds like it’s going to be an awesome build and lots of fun when finished Al


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[MK_WF]

Pipe building is one of my favorites
For example this is a RD500 set I did some 12 years ago


If you want to give it a try, check out my how-to: https://www.rd350lc.de/downloads/MK-Dok ... glisch.pdf

[tony.mon]

If you want to give it a try, check out my how-to: https://www.rd350lc.de/downloads/MK-Dok ... glisch.pdf

Wow. Great writeup and information, Martin, well done for making it public.

[fabiostar]

The great black art of spannies

[AMCQ46]

Pipe building is one of my favorites
For example this is a RD500 set I did some 12 years ago


If you want to give it a try, check out my how-to: https://www.rd350lc.de/downloads/MK-Dok ... glisch.pdf

Fantastic job, both the write up and the end result on the bike

[MK_WF]

Thanks folks.
Glad you guys like it :-)

[sirch345]

Pipe building is one of my favorites
For example this is a RD500 set I did some 12 years ago


If you want to give it a try, check out my how-to: https://www.rd350lc.de/downloads/MK-Dok ... glisch.pdf

I had a read of all your hard work last evening. Very interesting to read first hand information like this, even better with the added photo's

Many thanks for sharing Martin, plus all your tips and advice, it must have taken ages to put it altogether

Chris.

[sirch345]

Update from my trip to Leicester to see Harry Barlow.

It’s only 60 miles from mine so should have taken just over an hour, except for the 20 mins it took me to find his unit with google paps placing it in a building 50 yards up the road.

I Got to a place with the right house number but no signs on any of the doors, and from the outside it doesn’t look promising. I spoke to some guys having a fag at the main door and they said Harrys unit is further in the building. Inside it is like a rabbit warren of unmarked doors, but after 50 yards i see a load of scooters in the wide corridor. I open the nearest door and i guess this is the right place as it is crammed full of machines and racks of parts, a scooter on a workbench and there is a bloke welding up an expansion chamber.

So he looks over the engine and sees that the ignition side crank web has just started to move on the hollow big end pin, even though it is welded. The weld has cracked because the hollow pin shouldn’t have been used in a race engine as it cant generate the same interference fit as a solid pin. He puts the crank on v blocks and the ignition end has 0.012” runout…. Not good.

Crank is still using standard Yamaha rods and needle big end bearings, he thinks they are fragile under the power this engine should make, so when the crank is rebuilt he will fit carillo rods and updated bearings (and new solid big end pins) before balancing and welding

Then to the barrels.
there is too much clearance measured against the std size pistons, so this is why the piston skirt has failed (0.0055” when he wants .0025”)

So will need a rebore up to 2nd oversize (+.5mm) and fit modified Weisco DT200 pistons ( I am going to buy 4 sets just in case)

Next the cyl heads.
He is not sure this is his work (i knew it was done by someone up in Scotland, so he is correct) as the angle and compression ratio are not as aggressive as he would do, but he will need to machine the heads to match the piston crown angle for the new pistons so they will get reworked once the crank, pistons & barrels are built back onto the engine.


Bottom line is that there is too much work to be done between now and Sunday as he has committed work coming out his ears.

Plan is he will do the crank and rebore by the 13th, then I will build up the engine and take it back to him to measure and reprofile the heads and finish putting it together.

Then once engine is in the frame I will bring the bike back to him so he can redo the expansion pipes to the correct length and reinstate the cross-over and make sire they fit the frame and stay out of the way of my feet.

He also spotted that the stingers on the pipes are different sizes! One is 25mm ID the other is 23mm!, so they need cut of and matched!

I was looking at some of the pipes he was making for scooters and it is an art.

He has loads of flat paper templates for each section of the pipe which he uses to cut out thin steel sheets. He then rolls them into a ring or a cone, and puts 1 tack weld in to hold them together, then he then he arranges the sections in 3 dimensions to create the snake curves to work round the other bits of the bike and puts a couple of tack welds in to hold them together, till it all fits the bike… up to 30 shapes all numbered.

Then once off the bike he fully welds all the seams and then he heat treads the weld zone to reduce the risk of cracks….. proper engineering porn.


So for Sunday 7th Run What you Brung at Santapod, I just have to decide am I going on the storm or the KTM

Interesting to read where you are with this engine atm

I imagine this has turned out a lot different than you were expecting Al. A good job you hadn't run it down the dragstrip as it was with just new pistons.
It was interesting to read about what your man does to build the two stroke pipes, then see Martin's work on the very same thing

Chris.

[tony.mon]

We'll be riding into a strong headwind at Santa Pod on Sunday (just getting my excuses in early!).
But at least it looks dry.

[Duffy1964]

Tony If you wanna go fast I still have my Ducati Multistrada


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[tony.mon]

Tony If you wanna go fast I still have my Ducati Multistrada


Sent from my iPhone using Tapatalk

It's ok, Duffy. I've worked out how to disable the traction control now.