Nanno's "mule" a TR1 for everyday


This thread is actually missing some of the updates that haven't happened all too lately actually.

After inspecting my old engine, I discovered that the distance between piston and squishband simply was too big to make the squish work effectively. (Quite the opposite really!) So after a lot of thinking (and admittedly hesitation to pull the engine apart again), I decided to take some measurements and win 0.5mm by replacing the base-gasket with some liquid gasket. So far everything seems to clear and now the piston to squish clearance is set at 1.20-1.25 (inaccuracies of my vernier caliper), which is still about 0.15 to 0.20mm more than I wanted but a whole world better than the 1.75 to 1.80mm that I originally had. (There will be a longer explanation on the blog coming weekend, when I have a bit more time to spell it all out for those, who are interested.)



To be fair, I've never been really getting to terms with the concept of "good enough" and one of the thoughts that has been nagging me at the back of my head was me wondering: could the detonation in the old engine have been successfully countered by tightening up the squish. Even though before hand it has to be said, that the new engine came with a somewhat tighter squish of 1.71mm (measured on the rear piston) than the old engine, which was closer to 2.00mm. In order to measure my squish-gap, I used some very soft solder with 2mm diameter.

Once that was done, I whipped off the head and inspected both piston and head and could find no abnormities. Except for a bit more carbon buildup than I am fully happy with, but no signs of detonation or the like. The circular squishband of the 700 seems to work just fine, so I don't think that (for now) any adjustments to that are necessary.

In order to lower the cylinder (and thereby get the piston and head closer together) I left out the base gasket and replaced it with some liquid sealant.

A bit of it squished out again on the sides, but once dry, it can quite easily be peeled off and it should be nicely oiltight.

And the gain: 1.25mm of squish-gap between piston and head. I would have loved to get it even closer for more efficiency, but then that could have come round to bite once the tolerances in the engine start to add up.

Modern literature states that a squishband becomes dramatically inefficient, once the gap exceeds 1.70mm, so to say I have some great expectations for this engine is a mild understatement. Regardless of what I wrote further up, this will be the last mod to this engine, unless it turns out not to be working as desired as I still have a turbo-bike to address and a second (currently broken) engine with a spare frame that I want to use for testing stuff like my welded up heads etc.



Gold Coast, Queensland
Re: Nanno's "mule" a TR1 for everyday

Very interesting design. It it a 2-1-2 design?


Yep, equal length 2-1-2, "just" like the old setup, but with a different rear downpipe (now the correct length exactly) and a different collector.

The whole setup is built so I can swap in different collectors as well to play around with those for performance reasons. (I actually want the collector to be a bigger diameter than the tubing for more top-end performance, i.e. from 1 3/4" (45mm) downtubes to a 2" (50mm) collector. I may end up building that collector from pie-cuts though, which is why I stayed away from that and did a 1 3/4" collector for a start.
with that sort of reduction in squish clearance it should be a lot less likely to detonate. you could have machined the base of the cylinder to go a bit further.

but it will impact the cam timing a fair bit. the cams will roll back as the tensioners will come out more so you'd get a few degrees retard with that sort of drop. which will also make it less likely to detonate as it'll lose midrange cylinder pressure. might be worth working out how to reset them.


Right, the attempt to build Mk.8 with a bigger collector failed, because my exhaust tubing vendor couldn't deliver 50mm (2") tubing with the correct radii. This made my original goals for building a new exhaust shrink down a bit to: 1) mustn't touch anything (especially not the chain-gaitors) 2) all the sleeves should point in the right direction to prevent sealing issues 3) provide room for an O2-bung (even though I do not plan to use one in the near future).

Among the design criteria was to plan for the necessary room to install LONG sleeves to have everything seal up properly and of course two downpipes of equal length.

The afforementioned O2-bung, right after the first Y-collector

And what it looks like right now (almost) done:

More pictures and more background infor on the Blog:


Let there be music (because the overall video quality isn't much to write home about):


Now that's (sort of) a first: working against performance and towards everyday reliability and longevity.

Step 1: As suggested by Sepp Koch, I have started playing around with softer valve springs to give the valve train a chance to live a bit longer as the seatpressure of the stock valve springs, especially in a 700 or 750 is through the roof. I only shaved off about 10kg (100Nm) of seat pressure, but every bit helps.

As you may or may not remember, I replaced the base gasket, with liquid gasket in an attempt to get the piston closer to the squishband in the cylinder head. This works perfectly, but it has the downside, that every time you loosen the head, you have to re-seal the cylinder foot as the cylinder pulls up on the unsupported side, which is a bit annoying. Luckily the liquid gasket I chose can be cleaned off quite easily with some brake cleaner and a brush, so it was maybe an extra ten minutes per cylinder to get everything squeaky clean again. (Making sure no oil leaks onto the mating surfaces or not dipping your finger into the gasket goo is much more of a challenge!)

There is a slight shift in timing, even with a brand new timing chain, so ultimately (once the chain stretches a bit), I'll probably have to make an adjustable cam sprocket, but until then, we'll just earmark this as a mod to shift timing towards more torque. :cl:

Last but not least: a softer timing curve with less advance. I had some detonation issues on the old engine, so tuning everything towards running a bit softer should be a good thing, especially with the tightened up squish, I hope to have finally found a way to keep detonation in check. Oh and that curve from 8000 to 9000rpm going to zero, that's my little life-saver as the rev-limiter on Ignitechs works fine until you overshoot it, e.g. by missing a gear. (At least in older versions it did and I am too much of a chicken to find out, if it's good now.)

Bit more on the blog (as usual):


THIS is how a Yamaha XV should idle an be sync'ed...

(More to come)


Alrighty, I'll do it rather briefly - this post is still work in progress and is basically a hands-on guide on how to install VM38s on a Yamaha XV (doesn't exactly matter whether we're talking 700, 750, 920, TR1 or 1100 really)

(I'll add some more parts numbers, e.g. for the 2in1-throttle cable and the dimensions for the carb to frame elbows, once I have gathered them!)


The next post on here (and on my blog is about stock and softer springs for the VM38) - in summary two pictures should suffice. 25 percent less wire diameter, means pretty much 25 percent less force required to lift the slides. As you have to work two slides... well you can probably do the maths.

The softer spring is a VM34/55 and should be available from the same sources you buy your VM38 from.


This one's a dear one to me... running an Ignitech box under the tank, where it can get quite toasty. I had planned for ages to move it under the seat, just like they did on the 1100s anyway. This one really only applies to the older models (750, 920)


And last but definitely not least, a bit of a report on how the air-screw affects the mixture and how you find the proper setup with a wideband...

(The corresponding video was posted a few posts back)

Have fun reading:


I am sorry, but I have to be a bit efficient for once - I've built a new engine for the old Tractor, as my Virago-based engine had a bad habit of guzzling oil at high(-er) rpm, because of some piston to cylinder clearance issues. (i.e. worn beyond hope).

V-Star engine build (part 1) - mainly about turning down cylinders and modifying the camchain tensioners to work with the camchain guides out of a XV

V-Star engine build (part 2) - salvaging the parts from a BT1100 engine, incl. a quick 'n' dirty guide how to take an engine apart

V-Star engine build (part 3) - the actual engine build, with crank bearing replacements and cylinder case boring

V-Star engine build (part 4) - fried coils and ignition - meant as a warning that you shouldn't trust brand new spark plugs and went back to stock ignition.

V-Star engine build (part 5) - killed a starter and a solenoid and also sealed up the oil-pressure-switch with some liquid gasket.

Verdict on the new engine:

Reducing the rotating mass by a third (compared to the heavy Virago 1100 crank that was in there before), has got a tremendous effect. It may have lost notable amounts of low-end torque, but I can't say for sure, as the engine spins up so quickly that in real-life terms it doesn't matter anymore. With the heavy Virago-crank it was pulling like a tractor from 2000rpm onwards, whereas now it just runs past this rev-range and hits 3000rpm very, very fast and then almost instantly revs up 5000rpm. It is, undeniably, quite a different kind of driving experience and after ironing out the jetting (which is more related to going back to stock ignition), I expect the whole package to be substantially faster than before.


... or the story of a poor little engine, which doesn't know it's not even meant to exist. :cool:

The story starts with me being a bit unhappy about the engine, which I built lately. In essence, I've built the perfect race-engine, not much grunt down low, but oh-boy does it rev. (And make stupid power in the progress.) Unfortunately the specs said "everyday-engine" and it was rather bad at that compared to what I had before. So I inquired about combining the heavy crank with my BT/XVS/V-star rotating assembly and the universal answer was: don't. Prior to asking those questions, I had thrown some crude maths at it. (I will get into the intricacies of how and why this isn't very precise and you should do it differently in a subsequent post.) And worked out that the balance factor will go up, not realising that the new conrods have got lighter small-ends and that would limit the effects quite substantially.

stock XV1100

XV1100 crank with (heavier) XV1100 conrods and BT1100 pistons

XV1100 crank with light pistons and with the correct conrods as well
(The last calculation was done after I had the engine open and was able to extract crank and conrods.)

And with that being said, I went through my stash of XV1100 cranks, dug out the one that was in the engine before and cleaned and stripped it.

Pulling the engine apart revealed a nice surprise, the XV700 heads are working flawlessly with the tightened squishband as can be witnessed by the clean areas in the head where turbulence is happening.

A quick check of the clearances between crank and conrod revealed Yamaha hadn't changed their tolerance codes and I made a spot on landing in the middle of the tolerance field with 0.040mm clearance, when combining BT-conrods with a XV1100 crankshaft.

And there we have the unholy union, called bumblebee. Also my assembly lube is a bit stiff. :cl:

Then followed the usual steps of reassembling the engine.

Just to prove: These are actual BT-pistons

Put the cylinders on

No base gasket to improve squish, only rtv-silicone.

And then after assembling the rest of the bike, I gave the exhaust a quick wipedown - the smoke in the video below is from the oil burning off.

So what's it like: It's basically an XV1100 engine again, but with notably less vibrations. Actually hardly any vibrations at idle at all, which is almost a bit irritating. It has got low-down torque for miles and obviously it doesn't like to rev as hard or rev-up as fast as with the lighter BT crank. And incidentially it proved a point: a roughly 3 percent change in crank balance factor can be felt, if you compare them back to back. And also of course: bumblebees can fly. :cool:

(The full version is available on my blog under: )

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