MATCH­LESS MODEL X ................................

A very long time ago, Frank of this parish ac­quired a non-run­ning Match­less Model X as a project. In­evitably, he did noth­ing with it. Richard Ne­gus is a man who can, and in­deed did, and this is con­tin­u­ing story…

Real Classic - - News - Pho­tos by Richard Ne­gus

A very long time ago, Frank of this parish ac­quired a non-run­ning Match­less Model X as a project. In­evitably, he did noth­ing with it. Richard Ne­gus is a man who can, and in­deed did, and this is con­tin­u­ing story…

Re­mov­ing the clutch and pri­mary drive re­quired only nor­mal tools, al­though a stan­dard Nor­ton puller was adapted to pull the clutch hub off its splines, ad­he­sive hav­ing been used at the pre­vi­ous assem­bly. Hav­ing re­moved the clutch and chain­case outer cover, the pri­mary drive and chain dy­namo drive were ex­posed.

Then the en­gine, sur­pris­ingly heavy even with­out its iron cylin­der heads, was re­moved and clamped in the bench vice.

With the cylin­ders re­moved, the re­sults of the seizure on both pis­tons could be ex­am­ined. The front pis­ton was only slightly dam­aged and, with mi­nor rec­ti­fi­ca­tion, could have been re-used. The rear pis­ton was badly dam­aged and be­yond sal­vage.

Look­ing more closely at the cylin­ders, each valve guide has a grease nip­ple as the only source of lu­bri­ca­tion for the valve stem. Those on the rear cylin­der had ob­vi­ously been very hot – per­haps the pre­vi­ous owner, as well as ne­glect­ing to turn on the oil sup­ply, also ne­glected to ap­ply grease here – and was that the real rea­son for the stuck valves and bro­ken cam fol­lower? I note the hand­book spec­i­fies ap­ply­ing the grease gun here ev­ery 500 miles, graphite grease be­ing the rec­om­mended lu­bri­cant.

Pis­ton crowns usu­ally carry a stamped iden­ti­fi­ca­tion to show that the pis­tons are ei­ther stan­dard size, usu­ally ‘STD’, or the re-bored over­size, ‘+010’, ‘+020’, etc. Th­ese pis­tons car­ried no such iden­ti­fi­ca­tion, but mea­sur­ing the cylin­der bore con­firmed that they were 0.040” over the stan­dard bore of 3.750”. The pis­tons were ob­vi­ously not orig­i­nal, be­ing grav­ity die cast­ings, and the in­side of each cast­ing car­ried the man­u­fac­turer’s part num­ber, in this case 34193 and the man­u­fac­turer’s logo ‘AE He­po­lite’. A lit­tle re­search showed that th­ese pis­tons were orig­i­nally pro­duced as orig­i­nal equip­ment for a six-cylin­der Bed­ford TK truck en­gine. To adapt them to the Match­less en­gine, the top of the pis­ton had been ma­chined slightly to main­tain the stan­dard com­pres­sion ra­tio.

As the rear cylin­der bore was quite badly scored from the seizure, the re­build re­quired them to be re-bored to +0.060”. A well­known spe­cial­ist pis­ton sup­plier of­fered an en­gine set of six pis­tons at an im­prob­a­bly high price, but a search of that equally well­known on-line auc­tion site pro­duced a set at a third of that. The po­ten­tial down­side of this trans­ac­tion was that the seller was at Li­mas­sol in Cyprus. I needn’t have wor­ried, as An­dreas despatched them straight away and they were de­liv­ered to my doorstep three days later, still in their orig­i­nal AE He­po­lite pack­ag­ing.

You might won­der how an orig­i­nal set of Bed­ford TK pis­tons ended up in Cyprus. My guess, based on An­dreas’s ex­ten­sive list of other items, is that he deals in ex-mil­i­tary spare parts, the Bed­ford TK truck was a

favourite of our mil­i­tary, and that Cyprus has been one of our out­posts for many years.

Some­what sur­pris­ing were the hand-made alu­minium plates be­tween each cylin­der and thet crankcases. There was no ob­vi­ous rea­son forf them, ex­cept that with them fit­ted the crownsc of the pis­tons came level with the cylin­derc head joint face at TDC. With­out the plates, the pis­tons would have pro­truded by 1.22 mm (0.048”), bring­ing them very close to the flat face of the cylin­der. The re­place­ment pis­tons were ma­chined such that, at TDC, their crowns were level with the cylin­der face with­out the alu­minium plates fit­ted.

Fur­ther dis­man­tling of the crankcases re­vealed an­other sur­prise. The drive side main bear­ing ar­range­ment was sim­i­lar to 1938/39 fac­tory spec­i­fi­ca­tion, but this en­gine had been mod­i­fied to have a larger roller bear­ing, tak­ing the ra­dial loads, and a nar­rower ball bear­ing for ax­ial lo­ca­tion. There were shims be­tween this ax­ial bear­ing and the roller bear­ing in­ner race to, I as­sume, place the crank­shaft cen­trally within the crank­case. How­ever, wit­ness marks on the in­side of the drive­side case showed that it had been touched by the fly­wheel at some time and an ad­di­tional 0.010” shim was fit­ted on re­assem­bly.

With the crankcases and crank­shaft cleaned, oil ways checked with a pipe-cleaner (re­mem­ber those? I still have un­used ones and have never smoked a pipe), re-assem­bly com­menced with a dry run to con­firm that

the ad­di­tional shim at the ball bear­ing still al­lowed the crank­shaft to float in the cases. Then a fi­nal assem­bly was made us­ing Three Bond to seal the joint faces. As most of the crank­case fix­ings were also studs for the en­gine plates, the crank­case halves were clamped to­gether with slave bolts.

Next came in­stal­la­tion of the cam fol­low­ers, de­com­pres­sors, tap­pets and spac­ers. Pho­to­graphs taken dur­ing dis­man­tling helped, but se­lec­tion of which-spacer-wen­twhere was very much a case of trial and er­ror. With all in place and the de­com­pres­sor levers work­ing as in­tended, the cam was fit­ted and then the crank pin­ion in­stalled onto its key on the crank­shaft. Cam tim­ing was a sim­ple mat­ter of align­ing marks on the two gears. In­ter­est­ingly, there are only three cams on the camshaft to op­er­ate the four cam fol­low­ers. By a clever piece of engi­neer­ing, a sin­gle cam op­er­ates each ex­haust valve in turn.

Tight­en­ing the crank­shaft pin­ion nut re­quired a bit of ‘skill and judge­ment’ as none of the pe­riod doc­u­men­ta­tion con­sid­ered that the rider/owner/me­chanic might have ac­cess to equip­ment such as a torque wrench. For a skinny 9/16” nut of un­known steel, a torque of 40 lbs.ft seemed ap­pro­pri­ate. To lock the crank­shaft, I used one of the old pis­ton pins, resting on gauge blocks across the crank­case mouth; note that the thread is left handed. Af­ter tight­en­ing the nut, the tim­ing cover was re-fit­ted to hold ev­ery­thing in place and then the mag­neto drive sprocket tight­ened onto its ta­per.

An­other as­pect ap­par­ently not cov­ered in Match­less doc­u­men­ta­tion is that of pis­ton/bore clear­ance. In dis­cus­sion with the ma­chin­ing com­pany, we elected to use his ‘skill and judge­ment’, to­gether with his ex­pe­ri­ence of other side valve V-twin en­gines, par­tic­u­larly vin­tage In­dian, and set­tled for a nom­i­nal 0.004” to­tal clear­ance, mea­sured just above the bot­tom of the pis­ton skirt in the fore and aft di­rec­tion. Dur­ing this con­ver­sa­tion, I was amazed to learn that mod­ern liq­uid-cooled Har­leys, for ex­am­ple, run as lit­tle as 0.001” pis­ton clear­ance due in the main to the use of low ex­pan­sion hy­per­eu­tec­tic alu­minium al­loy to man­u­fac­ture the pis­tons.

Al­though only one ex­haust valve seat was slightly pit­ted, the op­por­tu­nity was taken to lightly re-cut all four seats. The orig­i­nal valves, and their seat faces, were in good con­di­tion and so were re-fit­ted. The sin­gle valve springs which, ac­cord­ing to the spec­i­fi­ca­tion should have a free length of 1.75”, ac­tu­ally mea­sured be­tween1.75” and 1.78” and so were re-used also.

In­ter­est­ing, but not un­usual for the pe­riod, the valve col­lars were re­tained by pins fit­ting through the valve stems; in this case the holes in the stems were elon­gated and the pins oval-sec­tion. More mod­ern en­gines usu­ally use split, ta­per-seat­ing cot­ters that fit into a ma­chined groove around the valve stem. Th­ese pro­vide a pos­i­tive lo­ca­tion be­tween the valve stem and spring col­lar but, as Nor­ton twin own­ers know well, are much more fid­dly to as­sem­ble.

In or­der to check that the new pis­ton

crowns did not pro­trude above the cylin­der/ cylin­der head joint face, a dry assem­bly of one pis­ton (with­out pis­ton rings) and its cylin­der was made. At TDC, the pis­ton was in fact 0.38mm (0.015”) be­low the joint face and thus should not touch the head gas­ket which has a slightly smaller bore than the cylin­der. I doubt that a re­bore of +0.060” was con­sid­ered when the cop­per/non-as­bestos gas­ket was orig­i­nally de­signed for this en­gine.

Fi­nal assem­bly com­menced with lightly grind­ing-in the valves, fit­ting springs and col­lars, and then lu­bri­cat­ing the bores. Pis­ton rings were re­placed, with the gaps equally spaced, and lu­bri­cated well, the cylin­der base gas­kets coated with Wellseal on both faces and, us­ing a pro­pri­etary pis­ton ring com­pres­sor, the cylin­ders were fit­ted and the three 7/16” base nuts tight­ened in se­quence.

Ig­ni­tion tim­ing, ¼” BTDC, is done on the rear cylin­der and as the mag­neto is not mounted di­rectly to the en­gine, but to a plat­form on the front en­gine plates, this can­not be done un­til the en­gine is se­curely back in the chas­sis. And, as the spark plug hole is dis­placed side­ways from the cylin­der bore mak­ing ac­cess to the pis­ton height im­pos­si­ble, assem­bly of the cylin­der heads was left un­til af­ter ig­ni­tion tim­ing was com­pleted.

Valve clear­ances were set to the spec­i­fied 0.004” in­let and 0.006” ex­haust and the valve cov­ers re­placed us­ing new rub­berised cork gas­kets. Each valve guide was given a good ‘squirt’ of graphite grease via its new grease nip­ple.

With the en­gine now in­stalled in the chas­sis and the mag­neto and drive chain loosely as­sem­bled, at­ten­tion turned to set­ting the ig­ni­tion tim­ing. Not hav­ing a dial gauge to mea­sure the re­quired ¼” BTDC pis­ton po­si­tion, I used a con­ven­tional dig­i­tal depth gauge and to de­ter­mine when the con­tact points were open­ing, the tra­di­tional cig­a­rette pa­per which is usu­ally re­garded as 0.002” thick­ness.

Help­fully, the mag­neto body was stamped ‘1’ and ‘2’ at the high ten­sion pick-ups but there was no such mark­ing at the cam ring or the con­tact points. Re­mov­ing one pick-up al­lowed the po­si­tion of the slip ring to be viewed and hence the cor­rect lobe of the cam for pick-up ‘2’, the rear cylin­der.

With the rear ‘2’ pis­ton set at ¼” BTDC, the mag­neto ar­ma­ture was ro­tated un­til the cig­a­rette pa­per was just re­leas­ing from the con­tact points. At this the sprocket nut was tight­ened enough to fix the sprocket to the mag­neto ar­ma­ture and the crank­shaft turned back­wards slightly un­til the points closed and the pa­per re-in­serted. Now ro­tat­ing the crank­shaft for­ward un­til the pa­per was just re­leas­ing, the pis­ton po­si­tion was re-mea­sured. Even­tu­ally, af­ter re­peat­ing the process twice more, the re­quired fig­ure was achieved and the sprocket nut fully tight­ened.

The mag­neto drive is lu­bri­cated by grease

Above: The Bur­man clutch – like its Ariel equiv­a­lents – lives out­side the pri­mary chain­case and runs dry. A pre­vi­ous owner had as­sem­bled the clutch us­ing ad­he­sive of some kind, so a puller was re­quired to re­mover it, af­ter which the chain­case outer could come off, re­veal­ing the typ­i­cal Match­less pri­mary set-up, com­plete with the chain drive to the dy­namo, which lives be­tween the en­gine and the gear­box

Left: Once the chain­case is out of the way, it’s only a mat­ter of a lit­tle heave-ho to ex­tract the en­gine. The un­used bosses cast into the drive­side crank­case are for other – non-Match­less – ap­pli­ca­tions of the en­gine

Above: Yep: sure signs of seizure. Run­ning far too hot and with­out any oil will do this

One of the two cylin­ders re­assem­bled with ei­ther new or re­con­di­tioned parts. Quite a con­trast with the way it was when Richard dis­man­tled it

Pis­tons old and new. As new gen­uine Match­less X pis­tons are for some rea­son un­ob­tain­able, Richard’s used new items from a Bed­ford truck. Here’s one now

As was com­mon back then, the Match­less re­tains its valves like this, rather than em­ploy­ing split cot­ters

As well as things in­side the en­gine get­ting very hot, it be­came clear that the greas­ing points for the valves had been ig­nored for a long time

Left: Ob­serve the wit­ness marks in­side the drive­side crank­case, caused by the fly­wheels mak­ing con­tact. This is not a good thing, ap­par­ently

Above: Cam fol­low­ers old and new, bro­ken and not. Huge thanks to the guys who sup­plied th­ese

Cam fol­low­ers as­sem­bled – with plenty of lube – and await­ing the ar­rival of the camshaft

Model X camshaft. Just the three lobes, you will ob­serve; both ex­haust valves are op­er­ated by a sin­gle cam lobe

A lit­tle close ex­am­i­na­tion re­vealed that the X was orig­i­nally in­tended to use some­what heftier spark plugs than are com­monly avail­able now. Fit­ting the in­serts to con­vert them – some time in the past – ap­pears to have cracked the heads a lit­tle

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