Building new short stroke engine

Kvinnhering said:

Hey guys.
Thanks for the many interesting feedback. I am sorry that I answer so slow, but I've been busy this year and is going to be busy at work and at home in the winter too.

Roban
I agree that it would be interesting to test before and after the conversion and preferably testing with same dyno bench. It 's one guy who lives 5 minutes away so have this as a hobby, But he's busier than me!! :roll: Tried to test my bike this fall, but we did not have time.
The engine was already dismantled when I decided to build bulletproof short stroke.

Fast Eddie.
Maybe I should test it before I put on Fullauto head. Will see how it goes throughout the winter.

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It would be great if you could. Wouldn't it be great if more of us did so, and posted, and thereby 'added to the body of knowledge' re what works, and by what factors...?

Fast Eddie said:

Kvinnhering said:

Hey guys.
Thanks for the many interesting feedback. I am sorry that I answer so slow, but I've been busy this year and is going to be busy at work and at home in the winter too.

Roban
I agree that it would be interesting to test before and after the conversion and preferably testing with same dyno bench. It 's one guy who lives 5 minutes away so have this as a hobby, But he's busier than me!! :roll: Tried to test my bike this fall, but we did not have time.
The engine was already dismantled when I decided to build bulletproof short stroke.

Fast Eddie.
Maybe I should test it before I put on Fullauto head. Will see how it goes throughout the winter.

Click to expand...

It would be great if you could. Wouldn't it be great if more of us did so, and posted, and thereby 'added to the body of knowledge' re what works, and by what factors...?

Click to expand...

I think the problem is that evaluation of 'improvement' is often subjective. In my own case I know how long it usually takes to get down the straights on our local circuit and how the bike should perform in corners. I always count gears and because I raced the circuit for 12 years, I'm very consistent. Obviously a power and torque measurement (or curve definition) from a dyno gives a bench mark for two of about 8 variables involved.
The trouble is that if the power band moves you get similar results with different revs and gearing, which affects the way the bike squats in corners when you gas it, which then changes the line in the corner and how early you can gas it coming out. Most of us can only cope with four dimensions (variables) at a time. When there are more than four it comes down to pattern recognition.

acotrel said:

Fast Eddie said:

Kvinnhering said:

Hey guys.
Thanks for the many interesting feedback. I am sorry that I answer so slow, but I've been busy this year and is going to be busy at work and at home in the winter too.

Roban
I agree that it would be interesting to test before and after the conversion and preferably testing with same dyno bench. It 's one guy who lives 5 minutes away so have this as a hobby, But he's busier than me!! :roll: Tried to test my bike this fall, but we did not have time.
The engine was already dismantled when I decided to build bulletproof short stroke.

Fast Eddie.
Maybe I should test it before I put on Fullauto head. Will see how it goes throughout the winter.

Click to expand...

It would be great if you could. Wouldn't it be great if more of us did so, and posted, and thereby 'added to the body of knowledge' re what works, and by what factors...?

Click to expand...

I think the problem is that evaluation of 'improvement' is often subjective. In my own case I know how long it usually takes to get down the straights on our local circuit and how the bike should perform in corners. I always count gears and because I raced the circuit for 12 years, I'm very consistent. Obviously a power and torque measurement (or curve definition) from a dyno gives a bench mark for two of about 8 variables involved.
The trouble is that if the power band moves you get similar results with different revs and gearing, which affects the way the bike squats in corners when you gas it, which then changes the line in the corner and how early you can gas it coming out. Most of us can only cope with four dimensions (variables) at a time. When there are more than four it comes down to pattern recognition.

Click to expand...

You made me larf there old chap "I always count gears" you say... I raced for a good few years and wasn't bad (on a good day) but apart from knowing I was in first on the start line, and 2nd, 3rd thereafter... I'd lost count by the first turn usually !!
Used to drive my 'mentor' Dave Degens to disstraction "what gear are you exiting Gerads in?" He would ask, only to be confronted with the utterly unhelpful reply "no idea" !!

I wouldn't know which gear I take any corner with on our local circuit except for about two slow ones which are usually second gear. When I practise I count and try to be in the same gear in the same places around the circuit each lap. I also work up to the corners until I start to lose control. I try braking later and getting on the gas earlier while staying smooth. If you lose count doing that you can get a nasty surprise.
It is the reason I stay away from our Broadford circuit. The Norton self-steers a fair bit and comes on with a rush, a few of the corners are over hills and are blind, and it is very twisty. I've never raced there and I don't believe I would learn it properly even over a 3 day race meeting. Our circuit at Winton is straight forward and safe and I can ride it without thinking too much.

a racer even at club level would know what gear to be in at a given corner,same as his brakeing points and when to get back on the PETROL

I'll take a short stroke anyday - unless going for big displacement. Even at 80.4mm stroke its still a long stroke in my opinion because the stroke is generally greater than the bore. With todays improved heavy duty bottom ends and lighter reciprocating high performance parts, a racing short stroke will be a reliable race winner and make a great street bike. If you're going to buy a new crank and go for the lighter reciprocating parts and limit to 850cc then I think it would be wise to have the crank made at the shorter stroke. There are too many advantages not to. You may even be surprised to see a short stroke 850 blow off a 920 for the same reasons that 327 chevys blow away 350s.

Well I wonder how the short stroek in Norway is going now?

Did you sort a lower tickover than 1100? And did you rev it to 8000 yet?

Mine is not really set for a tickover, closed throttle running is at 1500.....

Great power characteristics between 5 and 7, really strong between 6 and 7, occasionals runs up to 7500.

Steve

Except for displacement eh. What would it take to covert a 920 with light JSM kit to a shorter stroke with decent CR?

hobot said:

Except for displacement eh. What would it take to covert a 920 with light JSM kit to a shorter stroke with decent CR?

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An 82mm stroked crank and approx 3.5mm shorter than stock barrel height...

Hello Steve.

Sorry late reply. I spent too much time on message and upload canceled. I will try again tomorrow evening.

Fast Eddie said:

hobot said:

Except for displacement eh. What would it take to covert a 920 with light JSM kit to a shorter stroke with decent CR?

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An 82mm stroked crank and approx 3.5mm shorter than stock barrel height...

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Jim describes what you need to do to build and 80.4mm by 81mm 828 'square' motor with his parts including very long rods, its on his website .....it really depends on what you call decent CR....I am happy with anything over 10 and would choose to stay under 10.5

Might I dare to suggest that the Gentleman consider restoring into his crank cases a design feature Mr Hopwood so very carefully designed into his original Dominator engine to ensure the cam and followers did not suffer from premature cam and follower failure.
When Mr Hopwood and team designed the Dominator engine he included within the crank cases a camshaft oil bath which retained oil within it so that the cam lobes passed through oil ESPECIALLY during the engine start up period before oil became thrown about from the crank. It cost very little to include at the design stage.... To quote from a letter Mr Hopwood sent me dated 21-July-1981.....
'The camshaft tunnel of the Dominator was designed to retain as much oil as possible and in fact collected oil from the flywheel rim'. ' I would suggest that you make your fabricated elements from aluminium sheet of fairly substancial guage , say 0.080, also let the flywheel rim run within 1/8 to 3/32 of the cupped piece'.
Of course the oil bath would also collect oil draining down from the head once the engine was turned off thus ensuring it was full of oil for the lobes to dip into when the motor was next fired up days weeks or months later
A few years later I was reading the Piper Cams Tuning Notes publication and noted their comment that in their experience most cams that fail prematurely do so due to lack of lubrication during the engine start up period at which point galling takes place which ensures premature can and follower failure.......They also listed other causes such as installing a new cam but using non reground followers or not assembling everything coated in engine build grease or EP140 or whatever to ensure the cam and followers did not run dry etc etc.
I had previously stripped a friends vintage championship winning(??) olde 77 motor and with the head and barrel off turned the motor over fully expecting to find the cam minus a couple of lobes only to suffer severe shock at finding every cam lobe in perfect condition AND fully coated in oil. (That motor had stood on his garage floor probably a year with the drain plug / boulder filter removed). Never having ever seen this miraculous event occur before my tiny brain wondered if the oil bath the cam was running in which was clearly part of the original crank case casting was in fact a design feature and wondered if its progressive removal with every new version of crank cases produced over the years was responsible for the premature cam failures so many of us suffered...along with not setting up the valve springs correctly etc but we knew sweet bugger all in those days of youth ......so I contacted Mr Hopwood asking the question.......It really takes very little effort to write a letter or pick up the phone.....The trick is to have an address book with the names addresses and telephone numbers of real experts one can contact for factual information.
Things were NOT helped by such things as the Dunstall Tuning book showing a picture of someone attacking what was left of the oil bath with a rotary file to clean it out so that ones new super dooper go slower expensive high lift cam did not foul what was left of the tunnel thus removing even more of its oil retaining property, assuming it still had any to start with....
Incidentally Mr Hele on his Domirace motors fed a pressure oil supply to the cam which exited via holes in each lobe as did Mr Geoff Monty and Dudley Ward on their Monard Triumph engined race motors along with a gear oil pump. In my youth I spent a few weekends trying to learn from the ex AMC race mechanic friend who modified the cams and manufactured the oil pumps. One Senior (position not age!!)Triumph Service Gentleman once told me that at one time Triumph were replacing under warranty 25% plus of 650 exhaust cams...till mismanagement finally agreed to have the cams nitrided to make them even harder and wear resistant...well it was cheaper to do than introducing an oil bath or pressure fed lubrication system!!

Hello Steve.

It was nice to hear att you've got your bike on the road. Congratulations! It looks like we have the same experience when this comes to motor characteristics.

Here are status on my project last summer. This year have I mounted PWK 34 and MSD 4217 ignition with VR sensor (variable reluctance sensor) on the crank.



Engine idel at 1000 but it goes erratic. I think 900-950 is achievable with something more fine tuning.
Up to 4500 the engine runs well and comes on cam 4500 and going strong into 7500. And it's no problem to take it up to 8500 which is the limit I have in the ignition system.

I expect addition power of total power curve, especially in the upper register when I bolt on the Fullauto head with Big valves and port job done by Jim (it's ready on my shelf). But first I want to take a measurement on the dyno so I can see the difference Big valve Fullauto make.

But before that can happening I must sort out a problem and I need help to solve this. Engine missfier at 4500 RPM and it's impossible to get over this RPM. When I disconnect the alternator, the engine runs perfectly until maximum RPM. I think it's VR sensor which is influenced by the magnetic field alternator creates. I have tried to distance sensor as much as possible. I achieved 12 mm, but this is not enough. So now I wonder whether Hall effect sensor is sensitive to magnetic fields or not? Has anyone out there experience with Hall effect sensor and magnetic field. Please contact me if anyone has experience with this.

Kvinnhering said:

When I disconnect the alternator, the engine runs perfectly until maximum RPM. I think it's VR sensor which is influenced by the magnetic field alternator creates. I have tried to distance sensor as much as possible. I achieved 12 mm, but this is not enough. So now I wonder whether Hall effect sensor is sensitive to magnetic fields or not? Has anyone out there experience with Hall effect sensor and magnetic field. Please contact me if anyone has experience with this.

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Most definitely, as that's what Hall effect sensors are designed for. Since it runs fine without the alternator producing current, that's a pretty obvious indicator that charging current is triggering the sensors. Did moving the sensors out 12mm change how it runs? It's possible that you could turn the pickup and associated magnet(s) either clockwise or anticlockwise to get it away from the alternator poles. Can you take a picture of your alternator/crank trigger assembly? I'd be curious to see how the sensors lay in relation to the stator poles. There's always the possibility of placing a soft iron shield between the sensors and stator. A picture would help to better visualize that as a possible remedy.

Nathan

Hello Nethan.
I will post photos when I come home on Thursday evening.

Just love that photo by the fjord.....

I am nervous about getting above 7500, I guess I should see how happy it is up higher, but in a rigid mounted frame I am starting to feel a few vibes over 7250, I may have to look at balance factor which is currently high 70s.

I am still enjoying the ability to go to 7, change up, drop to 6 and run back to 7 change up, drop to 6.....well matched engine and gearbox....

SteveA said:

Just love that photo by the fjord.....

I am nervous about getting above 7500, I guess I should see how happy it is up higher, but in a rigid mounted frame I am starting to feel a few vibes over 7250, I may have to look at balance factor which is currently high 70s.

I am still enjoying the ability to go to 7, change up, drop to 6 and run back to 7 change up, drop to 6.....well matched engine and gearbox....

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Aim for 65% BF. Higher balance factors will just shake more front to back.

For smoother running at higher RPM you have to go for ultimate piston weight reduction. But there are diminishing returns. Drilled skirts save about 6 grams per piston. Tapered pins about 3 or 4 grams each. JS flat top pistons can be undermilled to save about 10 to 15 grams each (domed pistons are already undermilled). Thats about 35 grams total and there are machining costs. Another option is a heavier crank to absorb the vibes.

jseng1 said:

SteveA said:

Just love that photo by the fjord.....

I am nervous about getting above 7500, I guess I should see how happy it is up higher, but in a rigid mounted frame I am starting to feel a few vibes over 7250, I may have to look at balance factor which is currently high 70s.

I am still enjoying the ability to go to 7, change up, drop to 6 and run back to 7 change up, drop to 6.....well matched engine and gearbox....

Click to expand...

Aim for 65% BF. Higher balance factors will just shake more front to back.

For smoother running at higher RPM you have to go for ultimate piston weight reduction. But there are diminishing returns. Drilled skirts save about 6 grams per piston. Tapered pins about 3 or 4 grams each. JS flat top pistons can be undermilled to save about 10 to 15 grams each (domed pistons are already undermilled). Thats about 35 grams total and there are machining costs. Another option is a heavier crank to absorb the vibes.

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When I say 'few vibes' I mean I can just feel it, I have experienced far far worse, but because there is almost no vibration below 7000 I do notice it...I am pleased with how smooth it is but the design intent was to be able to rev up to 8000, maybe next time!

I had already had the crank balanced when the discussion on lower balance factors under 70 were discussed and I would have gone lower otherwise, I fully appreciate that people are having good experiences with figures below 70 in rigid mounted bikes.

It was asked for pictures of senor location and here are some. First photo are reluctor which replaces the original spacer.



I have machined down the outer ring gear of the sprocket and run with IWIS dublex chain from Andy (very good quality).









Nathan
To be sure so you mean that Hall sensor can not be used here? I know that Hall Senor is sensitive on the polarity of the magnetic field. If the magnetic field to stator have opposite polarity Hall sensor want, than this will not affect the Hall sensor?

As long as I used Sparx 3-phase altinator engine behave equally with sensor in this two positions (miss fiering at 4500). With the 1-phase orginal altinator miss fier engine by 4500, when the sensor was positioned as in the last picture. When the sensor was placed behind the stator miss fier it by 6500.

An alternative is to switch to a belt drive and placing VR sensor on the inside of pulley.

Kvinnhering said:

To be sure so you mean that Hall sensor can not be used here? I know that Hall Senor is sensitive on the polarity of the magnetic field. If the magnetic field to stator have opposite polarity Hall sensor want, than this will not affect the Hall sensor?

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That is a well thought-out system you've built! Very nice.
I believe the Hall effect will toggle with either pole, although it might invert the timing spike you are expecting.

Kvinnhering said:

As long as I used Sparx 3-phase altinator engine behave equally with sensor in this two positions (miss fiering at 4500). With the 1-phase orginal altinator miss fier engine by 4500, when the sensor was positioned as in the last picture. When the sensor was placed behind the stator miss fier it by 6500.

An alternative is to switch to a belt drive and placing VR sensor on the inside of pulley.

Click to expand...

In looking at your pictures (thanks for posting those), I wonder if it's not more of an inductive coupling between the stator's and sensor's wires as they exit the side cover. Have you tried running with the sensor wire pulled out of the grommet, away from the stator wires? No worries about running the chain dry for that long.

If that doesn't do it, I would look at building your sensor holder out of mild steel (the softer, the better) and design it so as to cover as much of the barrel of the sensor as possible, leaving the face of the sensor flush with the mount.

I believe Jim (Comnoz) has a home-brew crank trigger on his ride; I'm hoping he'll chime in here about any shielding issues he had with his.

Nathan