ESE's works engine tuner

[F5 Dave]

Well I spent some time putting the MB100 engine together a few times checking squish & chamber volumes. I had to modify a mandrel I had for holding the head as it suited watercooled heads & this is large & chunky aircooled. I’ve always got mates or local machine shops to adjust shapes with either “machine 0.2 off” instructions or anecdotal “take a little out” of the head amounts. For anything more serious I’d go there with an engine, burette & solder & we’d make a few cuts or I’d give them a template to follow that would get close to right.

When I got a lathe I always envisaged that I could do this myself, but I’ve doubted my 40’s lathe or mandrel was good enough to get straight sealing surfaces. Now my mandrel is straight this is a good start & I’ve made some cuts of the head squish area & chamber finding that the stock chamber wasn’t that straight compared to the head face or spark hole. Now they line up & the squish clearance is the same back to front & adjusted to 0.8mm.

I’ve taken the squish area back to under 8mm wide & measured compression. As I took successive cuts it came down from 15.2:1 to 14.7:1. Then I ran out of time but will snick a bit more out to aim at 14.3 so I’m not going crazy with air cooling for the moment.

MSV calcs are still pretty high like 25m/s, hard to get them lower & still retain some squish band.

The chamber height is quite tall & retains some of the std triangular shape despite being somewhat more squat than std top hat, but will do for the first runs. The next head I will cut quite some more off the sealing face & start again & later experiment with a toroidal shape. What I am having difficulty with is making curved cuts with my range of std cutting tools. I have some ground tools, but have never seen a curved cutting tool & sod knows how you’d grind one. Any lathe experts have a better idea?

[Edit] I’ve made an attempt at a curved cutter but it isn’t what you’d call that effective. Better than nothing but not flash. Can’t remember my old lathe book saying anything about curved cutters.

[jasonu]

[Edit] I’ve made an attempt at a curved cutter but it isn’t what you’d call that effective. Better than nothing but not flash. Can’t remember my old lathe book saying anything about curved cutters.[/QUOTE]

Mate, persist with the curved cutter. I made one last century and it worked fine. There was a bit of juggleing with squish clearence and width % and comp. ratio but I got it to work.

[husaberg]

F5 Dave;1130118939]Yeah those forks should have juust about enough travel.

Can't see what the swingarm pivots mods are, but my old MB50 frame stiffened up considerably with teh addition of a tube run above the pivot between the plates. However don't be as stupid as I was back then, test position with the chain on using large sprockets & more importantly consider sw movement. (had to cut a slot in mine).

Good point re forks Dave.
I must admit I hadn't really looked at the travel but no real issue to shorten the travel up a bit. The frame as it is now is pretty much std.
The mods I alluded to are the tank in the other pic as you had a MB5 you will understand the reference.
I was planning on plating the swingarm plates as the alloy swingarm is a little thinner anyway, but a little lateral bracing sounds like a good idea too, esp. as I plan to hack around the rest a bit. I was planning on doubling up the spars a bit but I am undesidered at this stage .Although I could of course install a larger spine with the monoshock inside it with a cut out for the carb? Maybe.
Note the swingarm pivot is slogged out o the clutch side I always meant to fix that must have forgot It used to wallow a bit on fast right handers.
Plan on getting grinder out this weekend regardless.

[TZ350]

The next head I will cut quite some more off the sealing face & start again & later experiment with a toroidal shape. What I am having difficulty with is making curved cuts with my range of std cutting tools. I have some ground tools, but have never seen a curved cutting tool & sod knows how you’d grind one. Any lathe experts have a better idea?

We have often hand ground up curved cutters for shaping small combustion chambers.

Afterwards any imperfections in machining the combustion chamber are linished out later with a battery drill and port polishing stick while the head is spun in the lathe, take your time and it will work out OK.

[F5 Dave]

. . . It used to wallow a bit on fast right handers.
Plan on getting grinder out this weekend regardless.

Once I braced the frame & inserted a RM swingarm my stiffened shocks (heavier springs & oil) that had seemed ok all of a sudden were too stiff as that part of the "(un)controlled frame flex" suspension was gone.

[F5 Dave]

We have often hand ground up curved cutters for shaping small combustion chambers.

Afterwards any imperfections in machining the combustion chamber are linished out later with a battery drill and port polishing stick while the head is spun in the lathe, take your time and it will work out OK.

Cheers guys, I'll have to keep experimenting with cutters. To grind them what do you use, I mean aside from the external cut done on the bench grinder, how do you get a curved internal recess?

[koba]

Does anybody remember which bike of the 80s had a remote preload adjuster ns400? suzuki impulse?I was thinking of adapting one

NC21 did. I may have one soon, depending on how I choose to deal with my pakatu rear shock.

[TZ350]

Cheers guys, I'll have to keep experimenting with cutters.

Our lathe is quite small and our cutters are not ground to the full size, the curve is ground into 1/4 by 1/4 tungsten blank and covers about a 1/4 or at most 1/3 of one side of the combustion chamber hemisphere and has the normal top and side rake. By taking progressive cuts and joining them up a fairly good result can be achieved. I have seen Darren make a complete curve out of 1" by 1" that worked ok in his big lathe.

Other lathe tools that have proved very usefull are ones ground on the end like a soup spoon (normal top and side rake) and by locking the saddle and by carfull free hand use of the two handles on the cross slide fairly good chamber shaping is possible.

Of course CNC would be the Bee's Knee's but this is Buckets and the racing Gods expect us to have a go for ourselves using whatever cleverness and oddments we can find.

[TZ350]

Been having a few issues with getting my bike to idle, would either not idle (not enough gas) or continue revving like mad, (enough gas and perhaps and air leak) so funnily enough turns out my bike had an air leak. Don't know that I should be admitting it on here, but I never got around to blocking the oil inlet hole in the side of the barrel.

Buckets ...... the best place on earth I recon to learn race craft and bike prep. Thanks for the posts, its very interesting to see it all coming together.

There are some great looking home builts being developed about the place, exciting times.

[ac3_snow]

Does anybody remember which bike of the 80s had a remote preload adjuster ns400? suzuki impulse?I was thinking of adapting one

I think I have one in my garage, don't ask what its off, could be an old nsr or could even be a yamaha pretty sure it was a 250 something, send me a PM if your interested.

[husaberg]

Once I braced the frame & inserted a RM swingarm my stiffened shocks (heavier springs & oil) that had seemed ok all of a sudden were too stiff as that part of the "(un)controlled frame flex" suspension was gone.

I guess that’s the problem with these old frames designed for 100km/h and plastic tyres I suppose.
The frame will be an interim measure. Not ideal but it will do for now.
Would like a pre 95 RS frame but can wait for one to pop up.
I have attempted some mockups ( please don't mock my photo editor skills) Number 2 is probably the frontrunner.
Looks kind of mk4 Seeley G50

Anybody know how wide the subframe rail are on the RS125 for the seat?

[RMS eng]

Cheers guys, I'll have to keep experimenting with cutters. To grind them what do you use, I mean aside from the external cut done on the bench grinder, how do you get a curved internal recess?

Dave, you send the head to me i have 4 different shape cutters for 100-125 heads and for RS125 heads, for a small fee.

chris 09 817 9500
RMS eng

[husaberg]

Just a small point re main bearings.
You should have the crank floating - ie spin the crank in a lathe with the rod taped down and polish the main journals so that the bearing inner race just slides on by hand.

I was just thumbing through tunning for speed 1948 edition amazingly it says exactly the same thing. I always thought Phil Irving was Clever bugger .The Vincent Black Shadow should have been a bit of a givaway though.

[RMS eng]

I was just thumbing through tunning for speed 1948 edision amazingly it says exactly the same thing I always thought Phil Irving was Clever bugger .

its been around for along time 74-75 TM125 and RM125 suzukis cranks had a floating fit on the L/H side main bearing.but after a while it damages the crank.

[wobbly]

"MSV is high at 25M/Sec", forget all that old shit - here is the go with squish.
In any race engine the squish height should be set at the minimum achievable,just shy of the piston tapping the head when overeved.
In a bucket where the norm is "only" 13000 there is no reason to have any more than 0.6mm.
The squish width based on MSV is a theoretical number of little relevance when we are running the piston in the powerband just short of hitting the head.
But with a parrallel squish ( ie curved same as piston dome rad - or a straight cut with minimal divergence) then in most cases we can use 40 to 45% squish area.
This generates MSV numbers in the high 30 M/Sec region.It has been stated in a few references that " high"squish velocity will bump up mid power and reduce the top end.
Yes, in a limited view of things it does.But now that we have digital programmable ignitions thats rubbish.
The high MSV increases turbulence in the end gases, this increases flame speed, and has the same effect as high com or too much advance.
Simply retard the timing and the rpm comes back, but you keep the power generated by better turbulence burning up more of the end gas trapped in the squish.

One point to remember is that the best radius on the squish corner into the bowl is no radius at all.A sharp corner with just with a rub of sandpaper to get rid of the ragged knife edge, works best.
And with any of the race type plugs we are using approx 1mm of unthreaded plug end should be protruding into the chamber.
The old B10EGV was originally designed to be used this way by NGK, but nowdays the trick plug is a R7376-10, this plug makes more power than any other tested with around +2 Hp better than an expensive Denso equivalent, here is the test i have shown before.

Here is a pic of one of several "form tools" I have used for years cutting chambers.
Now there are plenty around I always use CNC to generate a toroid insert, based on a CAD construction of the chamber, as its simply too hard to get a good shape ( and is a prick to measure properly) when doing it by hand.