Engine ID please

[Edgeflyer]

Can someone advise is this a Merco 49 or 35? It has a similar cylinder head to an Irvine 40 and a longer stroke. The capacity legend seems not to be there.

[Martin Harris - Moderator]

If nobody comes up with an authoritative answer, whip the head off, measure the diameter of the bore and the distance the piston travels from top to bottom in inches and work out the capacity. 

[Brian Cooper]

I am certainly no expert on the various Merco engines, but I have a .49 (bought new in 1966) and it has a twin plug head. 

Based purely on that, I would say the one pictured is (probably) a .35 

[PatMc]

The 35 had plain bearings & weighed around 8 oz without silencer. I think your's is either a 49 or a 61.  They both weigh around 16 oz..

[David Davis 2]

The 35 and the 29 shared the same crankcase, so did the 61 and the 49. Just looking at the picture and without a ruler to guide me, I'd say you have a 35.

[Paul De Tourtoulon]

Any help?.

 

http://sceptreflight.com/Model Engine Tests/Merco 35 (2).html

[Martin Dance 1]

Tj

he chances are is that the engine is a  Merco 50. The clue is the fact that the cast in capacity legend was machined off when the Merco range was taken over by I think Forest engineering. There were some capacity changes across the Merco range. I also recall that for a while the engines were fitted with an ABC piston cylinder set up. which coincided with the capacity change. Take the head off and check the cylinder material,

[Edgeflyer]

4 hours ago, Martin Dance 1 said:

Tj

he chances are is that the engine is a  Merco 50. The clue is the fact that the cast in capacity legend was machined off when the Merco range was taken over by I think Forest engineering. There were some capacity changes across the Merco range. I also recall that for a while the engines were fitted with an ABC piston cylinder set up. which coincided with the capacity change. Take the head off and check the cylinder material,

Wow That's brilliant detective work thanks. Definitely not the 35. Probably not the 49, so the 50 makes sense. How might I know if the piston cylinder is abc?

[Denis Watkins]

ABC ? Take the plug out so as there is no chance of forming the resistance of compression.

Turn to motor over slowly by hand and you should feel resistance over the top of the stroke with ABC

[Martin Dance 1]

Edge flyer. Having thought about the motor  a little more, If it's an ABC setup. Look into the exhaust port.rotate the crankshaft so you can see the top of the piston, if there isn't a piston ring visible it's an ABC motor. Providing the motor isn't too badly gummed up or the cylinder discoloured with exhaust residue you should be able to see the brass colour of the liner, otherwise take the head off and look at the colour of the liner top edge. There were capacity changes on the 29 and 35 too.I believe the 29 became a 30 and the 35 became  a 38 or perhaps even a 40. Both the 29 and 35 were plain bearing engines sharing the same crankcase casting. The 49 and 61 also had a common crankcase design.

[Edgeflyer]

Thanks again for that info. I will look into it. Mine definitely is not plain bearing.

[brokenenglish]

It certainly isn't a 35. They are all plain bearing.

The original Merco production 49 and 61 engines were marked (in the casting) 49 or 61.

So your problem stems from the fact that this isn't an "original" or a Forest Engineering engine.

There have been several other "remakes", in particular Premier Plastics and some organised by Ian Russell (Rustler Engines). These remakes produced some non-original sizes (40 & 50) and I think your engine must be one of those.

If you really want to know, then I could contact Ian Russell, who would know for sure. But be advised that there's a lot of wrong conjecture above...

[Edgeflyer]

That is interesting thanks. It would be very useful to get Ian Russell to have a look.

[Robin Colbourne]

There is a picture of the Merco 50 in the Allen Mercury and Merco article on AdriansModelAeroEngines.com.

It has a dark crankcase which ties in with the one in the first post.  There is also a picture of a Merco 35 of similar vintage with the prop driver extending back over the front of the crankcase, so it clearly isn't the 35.
The text mentions how the Premier-built Mercos had the name in a much bolder font, accentuated by machining the surface off the cast lettering.  Clearly that isn't the case on Phil's engine, so maybe it was a pre-production variant using old parts.

Adrians Model Aero Engines - Merco

 

One more thought; if the 49 & 61 shared the same crankcase, would a crankcase sold as a spare part have had the capacity on it?

This engine review of a Premier Merco 61 from 1991 has the same lettering and longitudinally split silencer as Phil's engine, only the '61' is there.

Scptreflight 1991 Premier-built Merco 61 Review

 

This Merco 50 Stunt on ebay has the cast capacity machined off, but has '50' stamped on the lefthand mounting lug:  Merco 50 Stunt on eBay

Edited October 18, 2022 by Robin Colbourne

[brokenenglish]

Robin,

Only one version of the 35 had the prop driver covering the front bearing (the Forest Engineering version). All the others didn't, so that isn't a means of identifying a 35!

[Edgeflyer]

Thanks Robin for providing that interesting information.

I don't think mine is a Premier. It had the original cross head screws which I replaced with Allen heads. The crossheads seem to be from the older Merco 49 61 era.

I'm thinking the chances are mine was a 50 produced in between the 2 eras, maybe as you say pre production.

It is identical to the one you found on eBay but with an RC throttle and no 50 legend stamped on the lug. Again that fits with the change over period.

The up shot of all this is it still seems a good bit of English engineering and may yet have life in it. I could put it back on the Buccaneer that it came on, which has been completely refurbished and originally had a Merco 49 hand written inscription on the fuselage. Maybe it will run and fly again.

[Edgeflyer]

eBay stunt version

Mine

Note pre production looking silencer

[Paul De Tourtoulon]

Can't you measure the swept volume ?.

[brokenenglish]

As mentioned above, I contacted Ian Russell, who probably knows more about Merco production than anyone on here.

I reproduce part of his answer below, but the bottom line is that the OP engine is probably a .49.

Ian says:

"Definitely not one from me.
The size was cast on the c/case, where the little circle is, below the C of Merco. The cases could be cast with either 49 or 61 where the circle is. Later they couldn’t be bothered with this, and had all 61 cases cast. Then if it was a 49, just spot faced the 61 away and stamped 49 on the side of a lug. It’s probably a 49."

I think that's probably the end of the story.