Muf­flers, Multi-Cylin­ders, and More

Email your ques­tions to Clarence Lee at


It seems like, lately, a month or two sel­dom goes by in which one of the ma­jor hobby-re­lated busi­nesses doesn’t close its doors. In the past six or seven months, Fox Man­u­fac­tur­ing ceased op­er­a­tion, as did Hobby Peo­ple with their mul­ti­ple stores and Macs Prod­ucts, the coun­try’s largest man­u­fac­turer of muf­flers, tuned pipes, header pipes, and re­lated ac­ces­sories. It was back in the mid-1960s that the change from .45ci en­gines to .60 size for pat­tern com­pe­ti­tion was un­der­way. Due to the larger en­gines, noise be­came a prob­lem at many fly­ing sites, and many clubs be­gan look­ing into muf­flers as a so­lu­tion. Wally McAl­lis­ter fore­saw the fu­ture and formed his busi­ness, Macs Prod­ucts. Af­ter more than 40 years, Wally de­cided to re­tire and turn the busi­ness over to his brother, Dave. This past Septem­ber, how­ever, Dave un­ex­pect­edly passed away. When no other fam­ily mem­bers were in­ter­ested in con­tin­u­ing the busi­ness, Dave’s wife put it up for sale. My good friend Randy Lin­salato, who in con­junc­tion with his wife, Anch­ing, own and op­er­ate MECOA/K&B, pur­chased Macs Prod­ucts. Randy does not in­tend to con­tinue any pro­duc­tion, but he did re­ceive a large in­ven­tory of the prod­ucts that he will be mak­ing avail­able. So if you are in need of any of the Macs Prod­ucts’ line of muf­flers and pipes, visit or call 626-359-6972.

Now to the let­ters.


am won­der­ing if you could en­lighten me and your readers about the de­sign of multi-cylin­der en­gines and, in par­tic­u­lar, ra­dial en­gines. Why do ra­dial en­gines al­ways have an odd num­ber of cylin­ders? The only even num­ber multi-cylin­der en­gines I have seen are al­ways op­posed.—Frank Jor­dan, Kansas City, KS

An­swer: Well, Frank, as most peo­ple with any en­gine ex­pe­ri­ence know, a four-stroke en­gine fires every other revolution (i.e., two rev­o­lu­tions for one com­bus­tion cy­cle). In the case of a 5-cylin­der ra­dial, the num­ber one cylin­der fires, skips num­ber two, and num­ber three fires, etc. On the sec­ond revolution, num­ber two fires, fol­lowed by num­ber four, and back to num­ber one. Since the en­gine fires one cylin­der and then skips one, there has to be an odd num­ber to come out even. Ra­dial en­gines use a mas­ter rod, with the other rods con­nected to the mas­ter rod and a sin­gle throw crank­shaft. Op­posed en­gines use a dou­ble- (or more) throw crank­shaft depend­ing on the num­ber of cylin­ders (i.e., a throw for

each pair of cylin­ders).


Our next letter from Cana­dian Ed Carew was ac­com­pa­nied with two pho­tos, nei­ther of which was suit­able for re­pro­duc­tion. Ba­si­cally, they showed a pis­ton with a big hole in the cen­ter and both rocker arms bro­ken. Ed’s club mem­bers felt the dam­age was caused by a stuck valve, but he dis­agreed and asked for my opin­ion. Read on.

I have been reading your col­umns for more years than I can re­mem­ber, and this is the first time I have writ­ten to you. The sub­ject mat­ter is a 15-year-old Saito .56 en­gine that quit abruptly in flight.

The en­gine had pre­vi­ously been very re­li­able in a num­ber of dif­fer­ent mod­els, in­clud­ing a Tele­mas­ter, Unionville Beaver, and Kaos 40. There has been a lot of dis­cus­sion in our club re­gard­ing the cause, with “stuck valve” be­ing the most pop­u­lar view. I have a prob­lem with that since it does not ex­plain the dam­age. I think the valve broke off the valve stem, bounced around the com­bus­tion cham­ber and made a hole in the pis­ton, jammed the ex­haust valve (thereby breaking the rocker), then was pushed up into the in­take port, which pushed the valve spring assem­bly out and broke the other rocker. This would ac­count for the dam­age, but what would cause the valve to break off the stem, and what would cause the re­tain­ing clip to break and the top of the valve stem to break off? With your many years of ex­pe­ri­ence, I am hop­ing you can pro­vide an ex­pla­na­tion of what might have caused this fail­ure. Note: I don’t think it is worth re­pair­ing the en­gine; I’m just cu­ri­ous about what hap­pened.— Ed Carew, Car­leton Place, ON, Canada

An­swer: Ed, in my opin­ion, I be­lieve your as­sess­ment is en­tirely cor­rect. The dam­age had nothing to do with a stuck valve. You did not say how much fuel had passed through the en­gine, but hav­ing seen use in three air­craft, it was prob­a­bly a lot. Dur­ing that time, it more than likely saw some lean run­ning, par­tic­u­larly to­ward the end of a flight, re­sult­ing in det­o­na­tion. Det­o­na­tion is a well-known cause in the au­to­mo­tive and full-size air­craft fields for breaking valves and pis­tons.


Our next letter is a lit­tle on the long side, but ex­presses a prob­lem that I am sure many of our readers have ex­pe­ri­enced when try­ing to dis­as­sem­ble an en­gine for clean­ing.

I have read all of your En­gine Clinic ar­ti­cles, start­ing with the first one way back when, and also your var­i­ous books on en­gines. I have had a prob­lem with an old Su­per Ti­gre .51 BB en­gine, which I would like to get your ad­vice on. I can­not re­call your ever ad­dress­ing this is­sue, ex­cept to men­tion that, on this type of en­gine, the wristpin must be pulled out with a wire us­ing a hook on the end. It would ap­pear that this en­gine was given Ris­lone af­ter-run oil many years ago, as it has green­ish marks. I would guess that the en­gine has not been used for more than 25 years or more. The en­gine was nearly stuck but would turn over. I put 3-in-1 oil in it, and it freed up pretty well. The cylin­der sleeve came out fairly eas­ily.

Then came the prob­lem. First, I tried us­ing the wire to pull the pin but could not even get the end pad out, even af­ter heat­ing the pis­ton. I in­verted the en­gine and filled the pis­ton cav­ity with WD-40 and let it soak overnight, with no suc­cess. I tried heat­ing it sev­eral times—again, no suc­cess. The rod was loose on the wristpin, so the pin had to be stuck in the pis­ton. I also tried your car­riage bolt trick to pry the rod off the crankpin, but there was not enough slack as it would only come about a third off and I had to tap it back into place. I then turned to a dras­tic method. I care­fully drilled a hole in the front of the case at ex­actly the same po­si­tion as the back hole. I used a slim flat-head punch through the front hole and care­fully tried to tap the pin out, but it would not move. I then used a press and fi­nally got the pin to move. It took con­sid­er­able force to push the pin out of the pis­ton. I was con­cerned that the pres­sure used might dis­tort the pis­ton, but it seems to be OK. Af­ter clean­ing the pis­ton and wristpin, they seem to have the proper slip fit, so it seems that the pin was stuck with dried oil.

Do you think the Ris­lone could have pos­si­bly caused the stuck pin? I have not en­coun­tered this prob­lem in any of my en­gines that have been stored with Ris­lone. Do you have any ideas as to how to re­move a wristpin that is as stuck as this one was? I would ap­pre­ci­ate any thoughts you have on this prob­lem. I know you can cut the rod and get the parts out, but with no re­place­ment rod, that is not some­thing to do.—James Leisk, Shreve­port, LA

An­swer: Jim, I can sure re­late to your wristpin ex­pe­ri­ence as I have run

into this many, many times over the years. If you ever run into this prob­lem again and can’t re­move the wristpin with the tip of a bent pin, use the tip of a round jew­eler’s file jammed into the wristpin hole. If this still doesn’t work, the end pad will have to be drilled out. Then us­ing an Easy Out, avail­able at any hard­ware store, will be re­quired. Easy Outs usu­ally come in a set of four. Easy Out, along with heat, will usu­ally get the wristpin out. Ris­lone is a good oil to use for long-term stor­age but, like oil, will even­tu­ally har­den. I do not like it for an af­ter­run oil as ex­haust residue will stain white or light-col­ored paint when the en­gine is run. I have found au­to­mo­tive au­to­matic-trans­mis­sion oil to be much bet­ter for long-term stor­age, and when mixed 50:50 with Mar­vel Mys­tery Oil or Air Tool Oil, it’s an ex­cel­lent af­ter-run oil.


I have been fly­ing RC air­craft for about 16 years, mostly with O.S. two-stroke en­gines. All was go­ing well un­til about a year or so ago when l started to have mul­ti­ple en­gine fail­ures. Up un­til that point,

I was the envy of our fly­ing-club mem­bers as I rarely crashed an air­plane and still have, and oc­ca­sion­ally still fly, my orig­i­nal SIG Kadet trainer with an O.S. .46 en­gine. Last sum­mer, I to­taled three very nice air­planes, se­verely dam­aged an­other one, and man­aged to dead-stick glide a few more back to the field with no dam­age. In all cases, all of these glow en­gines (five dif­fer­ent 0.S. en­gines and one Evo­lu­tion) just stopped dead, usu­ally in level flight. I have no idea what’s go­ing on!

Any sug­ges­tions? I love the RC air­craft hobby, but all this is leav­ing a sour taste in my mouth.—Dick Parkes, Kam­loops, BC, Canada

An­swer: Dick, if you ex­pe­ri­enced the same prob­lem with five dif­fer­ent O.S. en­gines and an Evo­lu­tion en­gine, which have proven to be some of the most re­li­able on the mar­ket, you ob­vi­ously have a com­mon prob­lem that you are over­look­ing. Two-stroke glow en­gines are pretty sim­ple in op­er­a­tion, and if they’re me­chan­i­cally OK and sup­plied with fuel and ig­ni­tion, they are go­ing to run. In your case, I would have to guess that it is a fuel-re­lated prob­lem. I be­lieve your prob­lem is ei­ther a stiff pickup line in the fuel tank that is not fol­low­ing the fuel as the tank emp­ties or you have a blocked or pinched muf­fler pres­sure line cre­at­ing a vac­uum as the tank emp­ties that, in turn, stops the fuel flow.


I am try­ing to catch up with my reading and just fin­ished reading your col­umn in the Fe­bru­ary 2017 is­sue. The “Hard Start” sec­tion drew my at­ten­tion as I have run into this dif­fi­culty be­fore and found that the source of the prob­lem was air leak­age in the in­take header/man­i­fold down­stream of the car­bu­re­tor. The en­gine would run quite well at top speed but would lean out at idle to the point of be­ing im­pos­si­ble to start at that throt­tle set­ting. Thanks for all the valu­able knowl­edge that you have been pass­ing on to your readers over the past 48 years.—Guy Lemieux, via email

An­swer: Thanks for shar­ing your ex­pe­ri­ence with us, Guy. It is al­ways ap­pre­ci­ated when our readers can help us solve prob­lems.

That does it for an­other one, gang. We’ll be back in the De­cem­ber is­sue.

Macs Prod­ucts’ uni­ver­sal muf­fler is avail­able for .20- to .60-size en­gines with ei­ther a strap-on or bolt-on re­tainer, depend­ing on the en­gine.

The 1945 Mor­ton M-5 was the first ra­dial en­gine to be mar­keted for model air­craft use. It weighed only 22 ounces and de­vel­oped about 0.5hp at 3,500rpm. It was modeled af­ter the full-size LeBlond en­gine and was de­vel­oped dur­ing World War II as a train­ing aid for air­craftengine me­chan­ics.

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