Tighter piston clearances

With the new availabilty of Nikasil coated aluminum cylinders and coated pistons it is possible to reduce Norton piston skirt to cylinder clearances more than ever.

Andy Molnars Nikasil/aluminum cylinders



John Sneads Nikasil/aluminum cylinders




4032 alloy graphite coated pistons go in with only .001" clearance to the coating in Nikasil cylinders.



4032 alloy molly coated pistons go in with only .0015" clearance to the coating in Nikasil cylinders.

2618 alloy graphite coated pistons go in with .0015" clearance to the coating in Nikasil cylinders.

2618 alloy molly coated pistons go in with .0025" clearance to the coating in Nikasil cylinders.

Even though all these types of pistons (including bare metal 2618 alloy pistons) may all have the same clearance when hot - some Norton owners like the idea of tighter clearances when the pistons are cold (no rocking or rattling when the engine is cold).

Some pistons such as Wiseco come provided with a molly coating. The after market graphite coating must be applied by L2L to bare metal pistons such as J.E. and Gibtec. Only Wiseco and Gibtec offer the 4032 alloy in some sizes. J.E. pistons come in 2618 alloy.

A
Thou
And
A
Half
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Do tight pistons give you better gas sealing ? - I thought that is why we have piston rings. My 850 motor is very loose and I run it on methanol. Even when it is stone cold, I do not hear piston slap. But when I start the motor, I never rev it straight away - I always let it idle until it gets some heat into it.
If you are using light pistons with short skirts, I could see some benefit in having them tight. I have always found a loose motor to be faster.
I would like to have aluminium barrels on my motor, because they are less weight to push around. But my motor has cast iron barrels and it loves methanol fuel, because it runs much colder. Even on a cold day, when you came in from racing, the motor is still very hot. Getting the same motor going as fast on petrol would be a major problem. The main objective with running the pistons tight in Nikasil coated aluminium barrels, is the probably the possibility of hammering the coating - it might spall and come off. That happens with chrome plated aluminium barrels on Yamaha two-strokes.

10 thou clearance might be a bit much , accy . but definately loose . Likely to go sideways .
Sorry .
INCIDENTLY ,
Just seen a control line aero video on the tube . Double Star A A C ringed engine .
Early ones were A A C . Alloy Bore . Alloy Piston , Hard Chromed Bore .
( a aside - Some ( others ) were what they called ' plasma ' coated .

which I assume is much like / akin , to Nickasil - a trade name .)
To cut a short story long . Super Tigre around 1974 pioneered ' A B C '
Brass Hard Chromed liner . With Silicone Alloy piston .
These ran a gnats dick of TAPER in the bore . The piston ' pinched ' at Top dead Center ,
from say 10% stroke below .
From new ( alloy block ) tight ones were best pre heated with a heat gun .
The Matched expansion - The Liner actually expaned more than the low Expan. piston ,
were ' anti seize able ' ( to a degree ) as the hotter they got the greater the clearance .
The A A C , alloy chrome plated cylinder , was a lineage for less differential expansion , and lighter weight .
Being AERO . & brass being heavy . =====================
( S Tigre were the first to get 200 MPH radio and control line , with the G 60 RV ABC . around 1970 .
The 1965 G 15 FI was the most powerful , HP per displacement , powerplant on the planet .
around 0.7 Hp at 21.000 rpm from 2.5 cc / 0.15 cu in . Were later abc tune piped versions . 1968 .)

ANYWAY , the point being , the A A C RINGED Double Star .60 , 10 cc aerobatic engine ,
Urtnowski is commenting on its ' pinch ' , where it ' jams ' , COLD , at Top Dead Centre .
You belt the propellor over . To Start . The Instant Heat gets the Instant Clearance !

this or adjacent / that row ' tape ' ZERO CLEARANCE at T.D.C.

https://www.youtube.com/watch?v=JYItx2Pf4ZI

Windy Seafire #47 on youtube​

Phew .

These things run maybe 5 thou ring end gap . On a 24 mm bore diameter .

MAYBE 001 mm interfearance . Cold . Just at the top of the stroke with the tapered bore .
Theoretically the RING can still be FREE , with the Piston Tight. !

====================================================================
But we degress . My first thought was " Nickasil tecnology and process must have evolved
tecnologically , since the early examples " . ONE WOULD PRESUME .

The Alloy Barrel should offer better long term sealing , top & bottom . With the better matched
expansion to the head a cases . So weeping should be eradicated virtually .

Do you know where the barrels were cast ( I had someone try to tell me someone in melbourne
had had two pallets of alloy cylinders cast . Saying someone in England bought the lot and had
them nickasiled in liue of fitting liners )

In respect of comments on Dunstall Cylinders - Two Series of materials - Do you know the alloy Spec.
of the barrels there . --------------------------------------

Original Iron Barrells were more a sound proofing perogative , as well as skin flinting . Seeing the T100
from 51 ran die cast alloy linered barrels satisfactorally . The adherance ovelong to iron being another
antiquacey of the ' British Iron ' , you might say .

So good to see there might be something more ' airworthy ' now . Even though its only been 70 years coming .

With decent Alloys for the cases and ( steel ) for a crank , we might start to get somewhere with a Commando .
( It'd be worth looking at what material Cosworth used on the P - 86 as regards to the Crankshaft ! . )

I see Routt's Triumph Barrels were first something like 800 Lb tensile strength , later 1600 .

Are these Norton ones similarly worthy , to stand say T C & His Nitro ?

I have seen a forged Mahle piston out of a two-valve Jawa speedway bike which had the bottom of the skirt curled under without cracking.

INCIDENTLY !

Ive always ( Since Ive seen the followers ! ) assumed , they worked like one of THESE THINGS .



No Wonder they worked well . With that bloke involved , Newton ! . this being a Newton's Cradle . Apparently .

The Lifter being one end ball & the Valve the Other , So the cam ' threw ' the follower , and that threw the valve .
The Fling Fling type sound ( Not Clatter ) of my 2S with W&S springs , shimmed . And my 3S .016 clearance ,
I believe (d) emphisised this ? ? .

Well VAUGELY like one , anyway . The Cam Action actuateing the inirtia mass ( lifter ), through the ' disregard
the Mass ' Ridgid rod ( and arm - with its vertically equalising opposed acceleration ? ) the valve responding in
effect to the distant mass , by accepting it (follower - the lack of opposition to its initial acceleration - through the
semi elastic push rod . So that the elasticity release acceleartion combines ( cumulative ) to get the initial more
accelerated ! valve opening underway . Thereafter the primary accelerations occured , so as there being LESS
( substatially ) load and therefore (less ) resistance thereon , relaxing again ' over the top ' ( through max. lift )
being absorbed again ( elastically - Alloy push rod . Not insubstantial . Either . At That ! ) the accelertion in the
closing trajectory . Released accelerating the lifter . Perpetual Motion accelertion machine . Low Input . IF
the cyclic loads and pushrod is regarded as operating as a ' spring ' logitudinally ! There being measurable
( Microns ) cyclic , Length Variation , .

The Harmonics , if ' in tune ' enhance operation significantly .

If Hopwood HAD envisaged this , it would endear some respect , after all .
LOOKING AT IT ,
the initial reaction is the lifter & rod were borrowed from David Brown , or John Deere . Perhaps theyed figured
it all out beforehand !

Incidently - are Valve Clearances with the alloy barrel other than with the stock iron cylinder ? .

My old cases probably would not work with the Molnar barrels, but I sure wish I had a set of those beauties. I just put the just bored old iron barrels on my old motor about an hour ago and now what was a manageable amount of weight to get back in the little frame is going to require my son's help, or I might lose a finger or two. Getting old is cool, but a lot of strength goes out the window from being so cool and living the dream.

I would like to borrow a time machine just long enough to get back the strength I had at 24 years for the two hours I'll need to get that motor all bolted up in the frame.

Speaking of your pistons: The ring gaps for the rings that come on your Wiseco +.040 pistons are perfect in my new bores without any screwing around filing them. Gonna be a tight little motor. I may have to take it easy with your parts in my old motor or my cases could end up in a puzzle piece scrap pile in the middle of the road.

The tight clearances shown is the post at the top of this thread are to the coating - not to the bare metal. Bare metal clearances are still the same as shown below:

.0055" for 2618 alloy in iron liner
.0045" for 4032 alloy in iron liner
.0035" for 2618 alloy in Nikasil
.0025" for 4032 alloy in Nikasil

That's why there is a bare metal dot on the skirt in the image above, and a bit of bare metal at the bottom of the wiseco piston skirt - so you can make sure the piston has enough bare metal clearance.

The molly coating takes up .001" less than the specs above.
The graphite coating takes about .003" less than the specs above depending on how thick you want it applied.

The molly is a sacrificial coating that may or may not wear depending on how much the pistons expand. Generally its there to avoid scuffing on break in.

The beauty of the graphite coating is that you can apply it thick enough that clearances are all the way down to zero and it still won't scuff. But you have to put it through an hour of break in till the graphite burnishes off at the tight spots - on and off throttle etc. After an hour it will have the ideal clearance and piston skirt life is approximately doubled. As long as your piston has enough clearance between the bare alum and the cylinder wall you are fine - its OK for the graphite to be tight - that's what its designed for - to burnish away to the perfect clearance.

But nowdays with the Nickasil cylinders you can go approx .002" tighter than was ever possible with iron.

Schwany - The rings come dimensioned for an iron cylinder wall and thats way yours came out right. But customers with Nikasil cylinders will have to check the ring gap for the slightly smaller bore and file as necessary.

If all these numbers seem like a PITA the rule I follow is to use an exact 73mm or 77mm bore etc on iron cylinders and .002" less with a Nikasil bore. The pistons are dimensioned accordingly regardless of the coating or lack of. Wiseco J.E. and Gibtec are pretty good at nailing these clearances.

acotrel said:

Do tight pistons give you better gas sealing ? - I thought that is why we have piston rings. My 850 motor is very loose and I run it on methanol. Even when it is stone cold, I do not hear piston slap. But when I start the motor, I never rev it straight away - I always let it idle until it gets some heat into it.
If you are using light pistons with short skirts, I could see some benefit in having them tight. I have always found a loose motor to be faster.
I would like to have aluminium barrels on my motor, because they are less weight to push around. But my motor has cast iron barrels and it loves methanol fuel, because it runs much colder. Even on a cold day, when you came in from racing, the motor is still very hot. Getting the same motor going as fast on petrol would be a major problem. The main objective with running the pistons tight in Nikasil coated aluminium barrels, is the probably the possibility of hammering the coating - it might spall and come off. That happens with chrome plated aluminium barrels on Yamaha two-strokes.

Click to expand...

Tighter (cold) piston clearances contribute to longer ring life. Most ring wear occurs before the engine reaches operating temperature as the pistons rock in the bore before expanding to reduce skirt clearance in the cylinder.

jseng1 said:

If all these numbers seem like a PITA the rule I follow is to use an exact 73mm or 77mm bore etc on iron cylinders and .002" less with a Nikasil bore. The pistons are dimensioned accordingly regardless of the coating or lack of. Wiseco J.E. and Gibtec are pretty good at nailing these clearances.

Click to expand...

It should be noted that the Wiseco pistons Jim supplied were intended for a single cylinder engine according to the box label. Single cylinder air cooled engines (like a BSA B50 or a Porsche engine, which has separate barrels) get away with tighter piston/cylinder clearances. Same goes for watercooled engines. Application of the "hand rule" and my measurement results in a .0017" running clearance.

Bore before plating will usually be larger than the nominal bore.

- Knut

That was the olde bugbear / excuse . ( lecture )
The Alloy Barrels EXPANDED , You needed and could run TIGHT COLD CLEARANCES .

The running clearance - Operating Temperature - With the alloy expansion is more generous.
What ' they ' whined about , was ' piston slap ' on start up . Iron expanded less and damped the sound .
Wonder what air cooled Dewcatis & big riceburner singles run - clearance .

Anuver fing , was the alloy expanded away from the sleeves . So heat transfer was impeeded .
All this tecnology had me horrifed the 55 T100 R , a sleeve sliped a inch or so , ON THE BENCH .
Horified I thought it must be DOOMED . Can pay to not know too much , or not spook at obviously
not unsatisfactiry equipment . Dont Panic . etc .

ROAD TESTS in the 50s ' piston slap ' was often mentioned , usually in regard to cold / start up .
with words like QUITE coming up when the neigbours couldnt hear it . !

SO , Back to nikasil ( oweva yer spellit ) One Assumes , like everything else , the tecnique & material
may well be somewhat more refined after 50 od years . half a century of ' Aplication . '

Nikasil was introduced by Mahle in 1967, and initially developed to allow Wankel engine apex seals (NSU Ro 80, Citroën GS Birotor and Mercedes C111) to work directly against the aluminium housing.

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The JeeGwar V8 is it , Saves the weight of EIGHT sleeves . When theyre chasing every ounce , these days .
These , emptying a packet of Ajax into it , unfiltered on dirt roads , or loosing your cooling fluid and forgetting to stop , or using cheap & nasty oil , might get ' issues ' .

So PRESUMABLY , theres more suitable ' type ' oils . Ones more applicable to Nickasil Motors ! ??

Also a DECENT Filtration system for the intake - in a Hostile Enviroment ( desert ) would keep out the meanies . Why , Ive just fitted a 30 micron oil filter to the original 92 Falcon . OILING . Std is 50 or 60 ,

So a fancey pants modern high effecancy AIR INTAKE FILTER ELEMENT should give total forign matter exclusion . if the housings not warped or the rubber boots rooted .

The coating youd presume 10 times better adheared and somewhat more endurable than the original hand built half century elapsed early efforts . After all , a few have been done by now .
They must have learnt something .

Note ; The Air Cooled hard chromed alloy cylinder , ringed model aero ' Double Star ' ( asin the video somewhere ) Runnin ZERO clearance . Around T D C in a micro tapered
( Cylinder is coned , apex at top . tho near infinate ' coneing ' as its a few micron per inch .

The POINT BEING , these coatings are extremely hard . The Heat Transfer is Direct . Instant ' expansion ' at start up - according to the barrels materials composition .
The only real likely cause of ' picking up ' would be unsuitable lubricant of forign object injestion . So going for a truly sealed intke set up , with modern ' micro ' filter capeability ,
Likely theyre good for 100.000 miles under abuse - as some term racing ! , or indefinate - like 250.000 road miles , if you keep the airborne abraisive matter from injestion .

Use a decent filter element and see there are no leaks whatsoever . Silicon Sealant , I believe its called . Utilised Judiciously . If using the original cheap mangey tin filter housing assembly .
Better the M III Airbox sans ears & maybe ' improved ' entry . The hole Ea side there increased , with little taper enty shields cobbled up .

But something like K&N / Filtron Micro Filter Socks , slammed on the carbs , would eliminate many joints . Even if they arnt leaking oil .



You could fit them over these PROPER velocity stacks , and theres a chance the Concentrics might work well .
Pity theres no magnesium Concentrics about , nowadays . a SOCK type FILTER , just in case your wondring ,ding .

they would fit to THE FLANGE at the Carb End ! . the tree oles'r for venting . if youre WFO , unrefined stacks back feed , depress floats & Yr Lean - gone bad .
Do it once & Do It Right . !
Check for best avaliable partical size elimination , element . ( and you can get Heath Robinson out from under the Seat ! .


Simplify & add lightness . C.A.B.C.

Nikasil is short for Nickel Silicon Carbide. Silicon carbide is a very hard ceramic (much harder than steel) that can be dissolved in nickel. The nickel solution can then be electroplated onto the aluminium cylinder bore. The piston rings will then rub off the exposed nickel, leaving a very hard layer of silicon carbide to prevent the cast iron/steel piston rings directly contacting the aluminium cylinder. With this setup, the engine tolerances can be much tighter for better performance. The cylinder must be re-plated after it is re-bored, but Nikasil is extremely durable, so the cylinder does not need to be reworked as often as an iron or chrome cylinder.

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The general princaple was never to have direct contact between materials - OILING -
So as the lubricant was not eliminated . Hence run in proceedure - pre micro finishing .

Lubricant compatability . Will CASTOR OIL still ben O.K. or is it obsolette in referance to these . The Model Aero , pre mix lube , generally SOME Castor with ringed engines - as it Runs TO the Heat !

Hindrance is its gumming when stored . It sets like resin after a few years . Hence Combined synthetic & Castor , Rangeing from 1/2 & half , to 3/4 Syn to 1/4 Castor .

Maybe ' Combined ; oils would be far out , for RACING , with these . The T 100 R definately seemed smoother & FASTER on Castrol R Castor Oil . V good cusioning .
Though the new tech maynot need it , Maybe the old reciprocating parts benefit , under duress .

ANYWAY , your set up looks like the Bees Knees ( 60s far out acronym ) Be intresting seeing them ' On Track ' and going hard out . Videos Videos Please .

Should eliminate a few dozen leakey joints . No Leaks on a British Bike ! How will you stop the rusting ! .

( Fit the stock air box around that , if you want it ' off the shelf ' showroom appearing !?
or a custom Hi Pressure one if you want to do a ' booster ' . But then
the eccentric Velo Stacks start to be essential .

You Do Not want GRIT embeded in anyfing . So a shield about the filter would look Hi Tech if inteligently
done . Clearance for free breathing - polished alloy maybe . in Debri Path . If there is one ! .

ANYWAY , that things the SIMPLIST - Hopefully Available in a ' top line ' filtering material .

About cases (as mentioned by Schwany a few posts above) does anyone know if those through-bolt type barrels will fit without change (such like helicoils) in standard 750 cases?
Thks,
Laurent

I think if I had aluminium barrels, I would prefer to have steel or iron sleeves in them, even if the bore size had to be smaller. I have never played with Nikasil, All of my experience has been with chromium plating. When you hone a bore using a stone, the end of the bore gets less loss of dimension, so you end up with a taper. Chrome is a good wear surface, but it does not like impact. As the piston reaches he end of a tapered bore, the frequency of vibration increases, and so does the amount of impact. Also there is the issue of the surface retaining lubricant. Steel is softer and probably has more scratches from grinding.

Matt Spencer said:

To cut a short story long . Super Tigre around 1974 pioneered ' A B C '....

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Finished? (please)

You leave Hobot in the shade.

When I first got my short stroke 500cc Triumph, it had Wellworthy Alfin barrels. The threads for the head studs were cast into the tops of the cast iron sleeves, but several of them had cracked. The barrels were unusable. But if the threads had not been done that way, the head studs would either have to have been through-bolted or threaded directly into the aluminium with coaser threads. On a Triumph motor only 4 head bolts can be through-bolted.

laurentdom said:

About cases (as mentioned by Schwany a few posts above) does anyone know if those through-bolt type barrels will fit without change (such like helicoils) in standard 750 cases?
Thks,
Laurent

Click to expand...

No. According to Andy Molnar, the crancase "mouth" has to be opened up. In addition, the threaded holes will require helicoils, as is the case with the 850's.

- Knut

mdt-son said:

No. According to Andy Molnar, the crancase "mouth" has to opened up. In addition, the threaded holes will require helicoils, as is the case with the 850's.

- Knut

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That is why I did not do it on my old P11 750 cases. More machinist jail, plus I don't think the old cases are tough enough to handle anymore HP. Best option to me would be to build a Molnar motor with Molnar cases and barrels. Silly for a street ride. However, if I were to wake up tomorrow and be 20 years younger, I'd do it with Jim's additional parts just to say I did. A man has to have his enthusiasms.

This is the part number sticker on the Wiseco box for the left piston for a 74mm bore Jim sent me. I think he has these made to his spec but am not sure.

Schwany said:

This is the part number sticker on the Wiseco box for the left piston for a 74mm bore Jim sent me. I think he has these made to his spec but am not sure.

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Indeed he does. All Jim's pistons, including JE and Wiseco, are custom made to his specs.

Ken