Merco 35 Strip Down

[Andy J]

Can someone please advise how you disconnect the con rod on a Merco 35.

 

Currently have the head and back plate off but cant proceed in removing the shaft until I can disconnect the con-rod. Suspect I need to remove the piston sleeve first but its stuck firmly in place due to the burnt on caster-oil.

[Rich Griff]

Well well well, small world, mine is apart at the moment being cleaned.

 

I use hot oil, but I am extremely carefully.

 

I use a small camping Gaz picnic stove, an old saucepan and old car/m/cycle engine oil.

 

You need rags handy and do this outside.

 

I heat sufficient oil so the engine can get dipped and held in the oil for say 20 seconds or so, remove from oil and place on rag.

 

With a glove I insert finger into cylinder liner and rotate.

 

Once it starts to rotate I redip in oil and repeat until it rotates easily, then rotate and extract at the same time.

 

You can then carefully remove the Conrod from the crank.

 

Don't let the gudgeon pin fall out of the piston else cover side of rod position is lost.

 

You can mark the cover side of the rod, with majic marker...

 

Your next problem is the prop drive plate, it's split taper bit and washer.

 

Come back when the cylinder sleeve and piston/rod is out.

 

Mine is plain bearing c/case not ball race bearings.

 

I only strip engines to make sure the c/case lube groove is not gummed up with old caster.

 

Petrol will clean off gum initially then I use cellulose thinners.

 

I filter and reuse for cleaning  for ecomony

 

All high flammable so be very very very carefully, cooker stove OUTSIDE !!!

 

You do not need the oil very hot, you could use a heat gun or hot water....I use oil.

[Andy J]

Thanks Rich, did try heating up the cylinder with a blow lamp but the liner did not budge.  Will try again!

 

Prop driver came off easily using a hub puller.

[Rich Griff]

Blow lamp NO !

 

Try submerging the engine in hot oil again, take your time, resist resist resist gripping the cylinder sleeve spigot that fits into head.

 

You could soak engine submerged in petrol overnight...and clean engine as best as possible softening and brushing the gum off...

 

By the way does yours have a red fibre cyl head gasket ?

Edited June 26, 2021 by Rich Griff

[Martin Arnold 1]

I would have thought the hot oil method is a very inefficient and messy way of trying to move the liner, when enough heat from a heat gun will usually have it out.

With the heat gun you need to get the cylinder hot enough for the old burnt on deposits to start smoking.

Edited June 27, 2021 by Martin Arnold 1

[Martin Harris - Moderator]

I simply pop my parts in the oven when she's out!

[Martin Harris - Moderator]

Why the confusion Bob? Controlled temperature, even heating and clean...what's not to like?  Although the missus might not agree!

[Andy J]

Afraid your advice about not using a blow lamp and gripping the cylinder sleeve was not seen until after the event Rich. Nevertheless the engine is now apart with no apparent damage.

 

Gaskets was present on the cylinder head but no idea of the colour as I scraped it off in the cleaning process.

 

One screw on the cylinder head was missing so now need to establish if this is a metric or perhaps BA thread.

 

Was surprised there was no bearings in the engine, is this normal for small engines?

 

Carb is a latter version than on my Merco 61 so was tempted to do a swap. Venturi orifice on the 31 is a tadge smaller along with the fit to the engine casting so will retain both carbs on their original engines.

[PatMc]

1 hour ago, Andy Joyce said:

One screw on the cylinder head was missing so now need to establish if this is a metric or perhaps BA thread.

 

Was surprised there was no bearings in the engine, is this normal for small engines?

 

 

The cylinder head screw could be BA or Whitworth. I once refurbed a Mercp 61 & had to replace the damaged head screws. I couldn't identify the thread type so cleared out the existing thread with a No34 drill, tapped it 4BA & replaced the Philips head screws with Alan studs. Later discovered that the original screws were 1/8" Whitworth.

It's possible that 3/32" Whitworth may have been used on the 35. If BA then 6BA would seem a bit weedy for the job 5BA more likely.

BTW the prop nut is probably 1/4" BSF.

 

There is a bearing, it's phosphor bronze which was (possibly still is) the commonly used material on "plain" bearing engines. 

[Rich Griff]

In my 35, the crank bearing us same as the rest of the c/case, a slightly heavyish alloy.

 

The Conrod is a more shiny alloy, unbrushed.

 

i will measure the head screws on mine after this coffee break, all slotted machine screws.

 

ut seems on mine the missing carb grub screw may have "fallen out" is stye thread is partially stripped. No big deal as enough neat left to go one size up.

 

still searching for some brass suitable for spray bar repair/ remanufacture...

 

dont know why text is underlined...  Back later, lovely day here but football pitch trees swaying tooo much for helo/drone fun...

 

ps, consider making a replacement crankshaft as vibration using original crankshaft will be huge...

 

maybe small ball or needle roller bearings are available and could be used ?

 

coupling the motor to the shaft, good access when the cylinder head is off.

 

i assume the electric motors have a spigot for easy location/centering ?

 

Edited June 28, 2021 by Rich Griff

[Engine Doctor]

Hi Rich . Its underlined as you have probably clicked the underline icon at the top of the reply box 

 

E.D.

[Andy J]

Thanks Rich & Pat for the info on the screws. Tapping out the screws may not be a bad idea.

 

Is your cylinder head painted black as the one I have is either very badly burnt with caster oil or has been painted as some point in time.

[PatMc]

The original version 35 had pink/orange painted head. IIRC the 29 head was black.

[Andy J]

Out of interest what monetary value do these engines have as don't wish to butcher the engine just on a whim of trying to add an electric drive. Could just reassembly the engine and sell it on now that it has been cleaned up.

[Jon H]

On 26/06/2021 at 17:54, Rich Griff said:

Blow lamp NO !

 

Try submerging the engine in hot oil again, take your time, resist resist resist gripping the cylinder sleeve spigot that fits into head.

 

You could soak engine submerged in petrol overnight...and clean engine as best as possible softening and brushing the gum off...

 

By the way does yours have a red fibre cyl head gasket ?

 

 

Why no blowlamp? i use them all the time for heating engines up. You cant just blast it clearly as you will melt it eventually, but done carefully there is no issue. 

 

Dunking in petrol...no, it wont dissolve castor as castor is not soluble in petrol and you risk ruining all the seals and gaskets in the engine as they are not designed to see any petrol. 

 

WD40, 3in1, cellulose thinners, petrol. All things you should never use to free up/clean/service a glow engine. 

[Jon H]

1 minute ago, Andy Joyce said:

Out of interest what monetary value do these engines have as don't wish to butcher the engine just on a whim of trying to add an electric drive. Could just reassembly the engine and sell it on now that it has been cleaned up.

 

 

with a £5 glow plug fitted it will be worth about £5 ? 

[Andy J]

Thanks, hacksaw job it is then to get rid of the counter weight on the shaft. Paid £13 for the engine as that was the cheapest engine I could find on flea bay last week. Will be more careful in future as paid well over the odds for the OS FS-52 last month only to find it a non runner until I did a considerable amount of work changing the bearings and freeing up the valves.

[Andy J]

14 minutes ago, Jon - Laser Engines said:

 

 

Why no blowlamp? i use them all the time for heating engines up. You cant just blast it clearly as you will melt it eventually, but done carefully there is no issue. 

 

Dunking in petrol...no, it wont dissolve castor as castor is not soluble in petrol and you risk ruining all the seals and gaskets in the engine as they are not designed to see any petrol. 

 

WD40, 3in1, cellulose thinners, petrol. All things you should never use to free up/clean/service a glow engine. 

What do you use Jon to clean up burnt on caster oil?

[Jon H]

11 minutes ago, Andy Joyce said:

What do you use Jon to clean up burnt on caster oil?

 

Dont bother. If its only a cosmetic consideration just ignore it. 

 

The problem is you end up damaging stuff. On the outside of the engine some methanol and a wire brush will do, but you can kiss goodbye to the finish on the engine. Methanol and a toothbrush will clean the light stuff and not damage anything, but its a pretty low level clean. 

Internally, just leave it. Change the bearings, use synthetic oil fuel and eventually it will wash out the sticky castor. Burnt on charcoal castor needs physical removal with wire wool, scotchbrite etc. but again you risk damaging the finish of the components. A steel valve on a 4 stroke is likely to be ok, but you are pushing your luck on anything softer. 

 

An ultrasonic cleaner with the right solvent can work wonders, but as my OS40 fs will tell you, get the wrong stuff and it eats the aluminium. 

 

So we end up where we started. If its for cosmetic reasons, just ignore it. 

[Rich Griff]

Petrol does seem to clean of a gummy grubby engine, leaves lots of "crap" in the bottom of the small baking tin cleaning bath I use.

 

Cheapo cellulose thinners dose a good job as well but is more or less 3 times the price of petrol.

 

Methalated spirit works as well but is relatively expensive.

 

All of the above are a very real fire/health risk but I am very carefully.

 

I don't have the monies for a sonic bath.

 

Next gummy grubby engine to strip and clean will be Cox 09's then 049's.

 

I will do a before, during and after pictures and show the difference and crap sediment.

 

It is labour intensive taking time and effort and a paint brush.

 

I know john will service many more engines than me, and come across engines with really burnt on castor, and has a "time" factor to consider.

 

The magnum gp40 had really burnt on castor/staining but I may have been using an unbranded fuel in that. That did take take more effort to clean off the dark brown thick coating, cellulose thinners removed that.

 

Some people use brake fluid, I tried that, soaking overnight and didn't find it that good, very messy.

[Rich Griff]

For cosmetic reasons I agree.

 

I only strip down to make sure the lubrication channel from the main crank case forward, stopping just short of the front, to make sure it's not blocked/gummed up, as it was in the merco 29 and 35. The gp40 was the same, as was the annular groove in the paw 19.

 

The paw 19 was well grubby outside with baked on brown staining, and the exhaust silencer was well coked up, needing the baffle removed to clean the silencer properly. Maybe the blocked exhaust silencer was making the engine overheat a bit, running on MT D1000 since new.

 

Yes I know, can the cylinder sleeve be positioned in exactly the same position when reassembling ?

 

In short, no, unless it's "pegged".

 

The gp40 cylinder sleeve has a cut out on the spigot at the top of the cylinder sleeve, but the c/case is not pegged ?

 

I use a cocktale stick to clean the lube groove...and mt afterrun oil for reassembly.

 

The test run is as kind as possible, a few runs rich, weakening off bit by bit on second run onwards, untill final run "on song".

 

That's how I do it, you may have different methods/techniques, I am not afraid to try/learn new methods...

Edited June 28, 2021 by Rich Griff

[Rich Griff]

46 minutes ago, Andy Joyce said:

Thanks, hacksaw job it is then to get rid of the counter weight on the shaft. Paid £13 for the engine as that was the cheapest engine I could find on flea bay last week. Will be more careful in future as paid well over the odds for the OS FS-52 last month only to find it a non runner until I did a considerable amount of work changing the bearings and freeing up the valves.

I think you may need more than a hacksaw...what a pity, murdering a merco...

 

Might you consider selling the spray bar and needle valve assembly ?

Edited June 28, 2021 by Rich Griff

[Martin Harris - Moderator]

3 hours ago, PatMc said:

There is a bearing, it's phosphor bronze which was (possibly still is) the commonly used material on "plain" bearing engines. 

The chances are almost 100% likely that your car engine uses plain bearings!  
 

With the materials used in these engines, there might be a case for using a fuel with some castor oil but opinions are likely to vary!

[Bob Cotsford]

18 hours ago, Martin Harris - Moderator said:

Why the confusion Bob? Controlled temperature, even heating and clean...what's not to like?  Although the missus might not agree!

"I simply pop my parts in the oven when she's out! " - sorry Martin, just my warped sense of humour at play.   Still trying to get THAT image out of my head!

Ovens and engine parts - yes, done that myself, 10 minutes at 200C when getting bearings in or out.  Biggest was a Bonneville crankcase which I'd not fully degreased.  Oven chips were off the menu for a week or two after that one?.

[Rich Griff]

Motorcycle and other engines tend to run the camshafts in the material (alloy ) that the cylinder head is made from.

 

Yes they are usually pressure fed with oil, but some just rely on splash feed.

 

In my 1979  Ripmax modellers handbook/ catalogue, merco "black head" models are listed/shown.

 

My 35 had a black head.