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I just realized that the Suzuki GT550 has 62 mm stroke, just like the RD400. The GT was in a lot more moderate state of tune than for example the H1, with 50 vs 60 hp (manufacturers numbers, of course)

Now, if one could build a GT550 based 600, using 3 x RD 400 cylinders and heads. Then it would theoretically be 64-65 hp (since Yamaha said the RD 400 had 43 hp)

This surely must have been done by someone already? From the pictures I have found, it seems the cylinder spacing on the GT 500 should allow RD400 cylinders to be fitted. Most likely the stud holes would have to be welded shut, and new holes drilled and tapped?

Not about bikes but still....I haven't ridden any snowmobiles since the late 90's, back when the majority were still carburetted.
Today I was with my son testing a couple of Finnish made Lynx sleds. Lynx is pretty much a sister brand of Ski-Doo, so both under the BRP umbrella. One of the two was an 850 E-Tech twin (non-turbo). But holy crap!
Power and throttle response was mildly put scary, at least on the hard packed snow on the trail we rode on. I do not what power these are supposed to have, but it must be close to 150 hp... Just imagine that kind of engine in a 600 supersport type bike. Just lighter than any I-4 four stroke.....

Hi,
I have mentioned in earlier posts that I am less than happy with a pair of stainless Higgspeed exhausts I got for my RD350A. One of my complaints are the apparently oversized headpipes, which I would like to taper.
The straight header section, approx 120 mm from exhaust port is quite straightforward to fix, either by machining tapered sections from thick wall SS hydraulic tubing, or by cutting out a wedge, squeeze the pipe shut over a tapered mandrel, and re-weld.
The bent part is where I may encounter problems. Making pie cut sections of a straight tapered pipe is one way, hydroforming a new section is another, and cutting out a wedge, like described for the straight section is the third.
Any suggestions or recommendations on what would be the easiest way? The taper will be quite moderate, maybe 1 degree. Note that the material will be SS, so not the easiest to hydroform I guess....

Some of you may be familiar with older European 2-strokes, but for those who are not, Zundapp was one of the most highly regarded brands, until the late 70s at least. A Zundapp 50 was sort of the tiddler equivalent of a BMW 900 or 1000.
So check this out:

https://www.facebook.com/andisfunktionspunk/videos/1408224216416402/

130 km/h (81 mph) 😁

How large is the angle difference between AC and LC exhaust flanges?  Asking because I wonder how hard it would be to adapt LC/ YPVS expansion chambers to an AC RD.
Stud spacing/ flange design/ longer adapters/ mounting brackets is absolutely not a problem. Guess I'm a better machinist than TIG welder, although I do try occasionally :)
My "problem" is that many of the alternatives for AC RDs out there look slightly goofy. A lot of clearance between engine/frame and chambers on some, or the JL classics that just don't look right to me. And so on.
Anyone tried this? Or the other way around? I'd really like a set that tucks in as tight as possible under the engine. Also, RD350 AC and LC do really not differ that much alt all in port timing, the main difference would be the width/ size of the exhaust port, so I believe LC chambers should work OK on an AC in that respect.

A single cyl, 2 exhaust port Jawa. Impressive work.
https://youtu.be/H3s_CemOJ9c

I just came across this on YouTube:
https://m.youtube.com/watch?v=q-CEmz6mww8
Definitely a lot of high end parts used on this one.....

I currently have one set of 80s vintage Allspeeds, and a still unused det of Higgspeed (which appear to be more or less a simplified SS copy of the Allspeeds.
I am really not too happy with either, they hang a bit too low for my taste (too much air between chambers and engine).
The Spec 2 classics are the closest to my ideal with regards to looks, but I would really like SS pipes, a bit larger diameter silencer section (like in the attached pic of the Suzuki). And also an internal stinger like the Allspeeds have.
And the general appearance of the Kawasaki Dencos in the second attached picture.
Some may think that the JL Classics would be what I want, but I think they just look awkward.
Is there anyone out there that makes something like what I described?

Just received my 3D printed LH side cover. Just basically a mirror image of the RH side cover. In its raw, unsanded, unpainted form, it weighs 247 g. (Just under 9 oz)

In the FB Aircooled RD group, there is a member that makes 3D printed parts, among them new RH. side covers. He is now making me a mirror image cover for the LH side, so I can remove the Autolube tank, and replace it with this new cover. Basically keeping a stock appearance while saving a bit of weight.
I will have to come up with mounting brackets like those in the RH side, and the plan is to make the upper hooks part of my home made alloy battery box, avoiding any welding. The bottom bracket is something I will have to figure out as well.
Of course, having both covers replicated in CF would be the optimal overkill...... Together with an alloy fuel tank, that is ...

I just came across these on eBay:

https://www.ebay.co.uk/itm/154157115637?hash=item23e47ae8f5:g:BUMAAOSww3Bflzlo

As my OEM pipes look rather shabby, I am tempted to buy a pair of these. Do any of you have any experience with these headpipes?

I have not planned very well, as I am now at work, with access to milling machine, lathe , welders etc. But forgot to take a simple measurement before leaving home  :embarrassed:

C-C distance between the M8 bolts/ bolt holes for passenger peg/ muffler hanger brackets on my 74 RD350A.  (My memory is unfortunately not as trustworthy as it used to be....)
So if someone could get me that measurement, it would be great!

Just saw something pretty unique in a FB story. A 2 stroke Bultaco 350 speedway bike. How cool is that?

I have a RD400 rh side fork slider, that I would like to use on my 350. Will the 350 damper rods, etc. work with the 400 slider? Also, is there enough material around the seal to machine the outside to 350 dimensions?

Reason for wanting to do this swap, is just to have the caliper behind the fork. Ny

Some may already have seen this build, I just saw it on BikeExif. BST carbon fiber wheels and Ohlins fork and shocks. Extremely high budget, I'd say, but still tastefully done.
http://www.bikebound.com/2021/03/23/ultimate-rd/

Years ago, I welded in a patch in the frame crossmember under the engine, where the sidestand mount often breaks. And then welded in 3 threaded slugs, for a bolt on sidestand bracket.
Then I never got any further on this project.
But now I am going to work overseas, and will have time to work on it.
But I need to know the angle of a stock sidestand bracket. Just how many degrees it "bends down" from horisontal. A couple of pictures would be nice too.
From the side, and from front.

Today, I decided to remove the springs from 2 pairs of old Marzocchi shocks that were totally shot. I reckon the springs may be used on other shocks, like Hagon's, etc. , should I feel the need to mess with spring rates.
Anyway, instead of a proper spring compressor, I use 2 small ratchet straps, and my bench vise to compress the spring, like shown in the attached pic. It can also be done on the bike, if necessary. Then the straps are hooked to the swing arm instead of the vise.

I am seriously considering to order a pair of Spec 2 Classics for my 350A, as I think they look better than any other currently available alternatives, as well as having a good reputation for power. (F1 or JL pipes look a bit out of place on a mostly stock RD IMHO)
However, I think they would look even better with a slightly larger diameter silencer section. On pictures, it looks like around 2"outside diameter. I would like something around 2 1/2" or 65 mm.
In the 80s, Italian made Figaroli chambers for the 350LC were just like that. Looked nice, and had a wonderful crackly sound as well.
So my question is just what the silencer OD is on the Spec 2 Classics, and also your opinion on modifying them with a larger silencer tube and end caps, before chroming or painting.

As I now have removed the stock muffler hanger/ brake pivot/passenger peg plate on my 350, I can also remove the steel spacer, and use a shorter 10mm aft bottom engine mount bolt.
As I now am away at work until January, I have plenty of time for online parts shopping......

So what I need to know is what length of M10x1.25 bolt is required when removing the mentioned parts. Or alternatively, what is the outside measurement of the bottom aft engine mounting lugs on a RD350 frame (I will then add approx 10 mm for the nut, in case you wondered)

Lately, I have been working on converting my RD350A rear drum brake into cable operation, instead of the heavy and clunky linkages normally associated with rearsets.  Now only the pedal stop, brake light switch connection, and return spring is left to sort out.

Mead Speed in the UK have a lot of pattern parts for Yamaha race bikes, including these springs:

http://www.meadspeed.com/products/yamaha/ta125/rear-brake-pedal-spring/
http://www.meadspeed.com/products/yamaha/tz250-350/brake-spring

Before I can decide which fits best, I need to know the OD and length of the portion of the pivot piece the spring sits on/ around.

Please check if you have  TZ or TA in the garage 😁