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Well all of you should know me by now, im the bad man from the North with a happy go lucky attitude and always up for a laugh. What you may not know is two stroke tuning is in my skillset. I am 100% self taught on 2 strokes, however I have diplomas for 4 strokes and Turbo charged engines and have completed 3 training course with Turbo Technics in gas flow engineering, turbo control, and principles of pressurised induction.
After many years of being in the modelling hobby ive rebuilt a few engines, blown even more up, but never has there been a fully comprehensive engine rebuild thread. So here goes!
After my previous engine munched itself after the collapse of a rear bearing, I had to buy another.... Enter Sheryl AKA Trillian. She had a near mint Align 91H I could buy off her but it had sat a while and she thought it may be prudent to fit new bearings. So money was exchanged and this morning about 11am the bloody postman woke me up!! ARRRRRRGGGHHHHHH
It was my Engine WOOO HOOO so lets have a looksee
And looking a bit closer yep theres some rust in there
Now this rust is by no means any reflection on how Sheryl looks after engines. Nitro-methanol fuel is HYGROSCOPIC, which means it absorbs moisture. ERGO it will cause rust.
So lets start the tear down. OFF WITH HIS HEAD
As you can see, a nice burn pattern, no signs of previous nastiness, infact a bloody nice cylinder head! Which is also carried over to the crown of the piston
A lovely looking back plate
However looking inside we find more of this 'orrible rust!! ARRRGGGHHHHHH
So yes a rebuild is definately needed. It probably will run now, and run faultlessly. Im a bit OCD so this will never do!! SO take out the liner with something NON metallic to push from underneath. Mine was stuck fast so I gave my trusty toothbrush a smack with a pair of plies and it freed the liner off so I could pull it out by hand
then pull the conrod off the crank
And pull the piston out. Removal of the piston and liner now reveals in deatil the rust thats in there
Now you need to push the crank out, this bugger was stuck fast so heres a Kev Top Tip!! Refit the crank nut and give it a light tap with the palm of your hand.
and Voila the crank is out baby!!
And a better look at the bearings and inside the case
And finally remove the carb. This reveals that the heat isolator is a bit chewed where its been tightened. But this is nothing to worry about.
The carb holder o-rings are a bit split too, so ill replace these (I have spares)
.
Ok so thats the tear down. Lets move onto the refurbishment.
OK Lets start with the piston. As you can see its nice and tidy, a little bit of blow by nothing major and the ring looks in good nick too.
SO to dismantle the piston you need to remove the gudgeon pin clips. Now be careful these little buggers ping off at any excuse and soon as they hit the carpet they're lost for ever!
and then slide the gudgeon pin out and separate the piston from the conrod
The gudgeon pin is a bit burnt, but I should be able to clean this up no bother
Now VERY CAREFULLY lift the piston ring off with your finger nail, just ease it out of the groove and furcle it out
The piston is in great shape, but can still be improved, the oil scraper groove below the ring is sooted up, and the ring groove could do with cleaning
worryingly there is some burn marks UNDER the piston but I personally think that will be from blowby of the piston ring.
But the liner is IMMACULATE so all happy here!
Now to clean everything. We need something to remove rust but that WILL NOT damage the delicate alloys inside the engine. 3M Scotchbrite is the perfect tool!!
So with the scotchbrite I clean the carboniferous deposits off the OUTSIDE of the liner ONLY, the sides of the piston ONLY and the crank. The reason ive left the crown of the piston is the carbon build up actually aids combustion and starting.
And I also very carefully cleaned the carbon deposits off the 3 sides of the ring that DO NOT contact the liner. Now to remove the bearings. Make sure your Mrs/Mum is out and use the oven!! I use gas mark 3 for about 15 mins. What this does is expand the aluminium case away from the steel bearings and they will just plop out.
What I do now is leave the engine in the oven for 15 minutes. WHat happens here is the alloy case expands faster than the steel bearings which enables you to get them out easily. I also fold a small towel so I have somewhere soft to tap the engine
What I always do now is thoroughly degrease the casing. Im using hot water, my trusty toothbrush and some shampoo (Ran out of fairy liquid)
MMMM SHINEY, Now for the new bearings. I always fit the rear bearing onto the crank with the open side of the bearing cage facing rearward for extra lubrication of the bearings. Then throw them in the freezer for 15 mins and the case back in the oven. ALSO being back in the oven will evaporate any moisture.
Ok after 15 mins get the bearings and crank out of the freezer and the engine out of the oven. NOW YOU MUST WORK FAST!! fit the front bearing on the end of the crank so you can use it to push the bearing home
Once the front bearing is fully home slide the crank out and drop it in the back and using a wooden spoon push the rear bearing gently home.
Now just put the casing to one side to cool naturally. Onto the rebuild proper. Make sure the conrod is 100% spotless. There is an old saying my lecturer taught me in college. "Cleanliness is next to godliness". So with this in mind every part we put back in this engine MUST BE SPOTLESS. I have cleaned up the gudgeon pin with the scotchbrite and the coolant holes in the piston crown I used a pin to scrape all the carbon out of. So apart from the carboniferous build up on the crown itself the piston is spotless. Go ahead and refit the rod and gudgeon pin and clips. Making sure you assemle the rod in the same direction as yoy removed it and the piston is the right way round (dont ask yes I did get it wrong. On this engine aswell LOL)
Give the piston assembly a good soaking with the light oil, to make sure the groove for the piston ring is fully lubricated and carefully refit the piston ring ensuring the gap in the ring corresponds to the locating roll pin in the ring groove on the piston. And go ahead and refit the piston assy to the crankshaft.
Hopefully in that last picture you can see the coolant holes in the piston crown I spoke about earlier. Now using some light machine oil. I personally use food grade oil, drown the piston bearings and the whole inside of the engine with oil. Go mad it doesnt matter the more lubrication the better IMO. Also spray the inside of the liner. Then with the piston at top dead centre, carefully wiggle the liner over the piston. It will suddenly pass the ring and slide down, and then just press it home locating the little cut out with the locating roll pin in the casing
Now you can refit the head. DO NOT clean the carbon off it, just make sure theres no dust or hair etc. Do the bolts up in a cross pattern a bit at a time and then refit the rear case. I also fitted a heat sink off a pumped engine, for no other reason than it looks good! LOL
OK so thats the heart of the beast done. Now for the control. The carb. Really easy this. Just remove the screw holing the barrel, the spring clips for the needles and put them safe. Then unscrew the needle assemblies 1 at a time and then you will have a stripped carb in front of you.
Now one at a time unscrew the needles from their holders and check the o rings and the wear on the needle. Any wear at all on the needle itself means it will not perform as it should, and I recomend you replace them if this is the case. DO this for the high and mid needles
Then just check the low needle barrel make sure its spotless and the o rings are fine
Finally inspect the barrel for wear and dirt, taking express care to make sure the holes are all spotless at this will affect fuel metering if any dirt is in there.
Carefully replace all the needle assemblies making sure they are tight. and slide the barrel back home and refit the location screw. I personally gave the barrel a coating in light oil too to aid its movement. I do not recommend carb cleaner at all on a model engine. The reason being is the carb cleaner leaves very fine deposits when it evaporates. This can clog the fuel ways in a model engine as the tolerences are much smaller than on a car or motorbike. Just my personal preference, but I feel its sound advice.
Now you should have a completed carb.
Go ahead now and refit the carb to the engine and thats it you have now sucessfully rebuilt a nitro methanol burning 2 stroke compression ignition engine
I hope this is a help to some people. All of the methods I have used can be applied to any size heli engine, buggy engine etc. The main thing I have to stress is the inside of the engine must be spotless. Aslong as you take your time and ensure the engine IS clean as possible. Your engine will be fine for many gallons to follow.
Kev Davies
After many years of being in the modelling hobby ive rebuilt a few engines, blown even more up, but never has there been a fully comprehensive engine rebuild thread. So here goes!
After my previous engine munched itself after the collapse of a rear bearing, I had to buy another.... Enter Sheryl AKA Trillian. She had a near mint Align 91H I could buy off her but it had sat a while and she thought it may be prudent to fit new bearings. So money was exchanged and this morning about 11am the bloody postman woke me up!! ARRRRRRGGGHHHHHH
It was my Engine WOOO HOOO so lets have a looksee
And looking a bit closer yep theres some rust in there
Now this rust is by no means any reflection on how Sheryl looks after engines. Nitro-methanol fuel is HYGROSCOPIC, which means it absorbs moisture. ERGO it will cause rust.
So lets start the tear down. OFF WITH HIS HEAD
As you can see, a nice burn pattern, no signs of previous nastiness, infact a bloody nice cylinder head! Which is also carried over to the crown of the piston
A lovely looking back plate
However looking inside we find more of this 'orrible rust!! ARRRGGGHHHHHH
So yes a rebuild is definately needed. It probably will run now, and run faultlessly. Im a bit OCD so this will never do!! SO take out the liner with something NON metallic to push from underneath. Mine was stuck fast so I gave my trusty toothbrush a smack with a pair of plies and it freed the liner off so I could pull it out by hand
then pull the conrod off the crank
And pull the piston out. Removal of the piston and liner now reveals in deatil the rust thats in there
Now you need to push the crank out, this bugger was stuck fast so heres a Kev Top Tip!! Refit the crank nut and give it a light tap with the palm of your hand.
and Voila the crank is out baby!!
And a better look at the bearings and inside the case
And finally remove the carb. This reveals that the heat isolator is a bit chewed where its been tightened. But this is nothing to worry about.
The carb holder o-rings are a bit split too, so ill replace these (I have spares)
.Ok so thats the tear down. Lets move onto the refurbishment.
OK Lets start with the piston. As you can see its nice and tidy, a little bit of blow by nothing major and the ring looks in good nick too.
SO to dismantle the piston you need to remove the gudgeon pin clips. Now be careful these little buggers ping off at any excuse and soon as they hit the carpet they're lost for ever!
and then slide the gudgeon pin out and separate the piston from the conrod
The gudgeon pin is a bit burnt, but I should be able to clean this up no bother
Now VERY CAREFULLY lift the piston ring off with your finger nail, just ease it out of the groove and furcle it out
The piston is in great shape, but can still be improved, the oil scraper groove below the ring is sooted up, and the ring groove could do with cleaning
worryingly there is some burn marks UNDER the piston but I personally think that will be from blowby of the piston ring.
But the liner is IMMACULATE so all happy here!
Now to clean everything. We need something to remove rust but that WILL NOT damage the delicate alloys inside the engine. 3M Scotchbrite is the perfect tool!!
So with the scotchbrite I clean the carboniferous deposits off the OUTSIDE of the liner ONLY, the sides of the piston ONLY and the crank. The reason ive left the crown of the piston is the carbon build up actually aids combustion and starting.
And I also very carefully cleaned the carbon deposits off the 3 sides of the ring that DO NOT contact the liner. Now to remove the bearings. Make sure your Mrs/Mum is out and use the oven!! I use gas mark 3 for about 15 mins. What this does is expand the aluminium case away from the steel bearings and they will just plop out.
What I do now is leave the engine in the oven for 15 minutes. WHat happens here is the alloy case expands faster than the steel bearings which enables you to get them out easily. I also fold a small towel so I have somewhere soft to tap the engine
What I always do now is thoroughly degrease the casing. Im using hot water, my trusty toothbrush and some shampoo (Ran out of fairy liquid)
MMMM SHINEY, Now for the new bearings. I always fit the rear bearing onto the crank with the open side of the bearing cage facing rearward for extra lubrication of the bearings. Then throw them in the freezer for 15 mins and the case back in the oven. ALSO being back in the oven will evaporate any moisture.
Ok after 15 mins get the bearings and crank out of the freezer and the engine out of the oven. NOW YOU MUST WORK FAST!! fit the front bearing on the end of the crank so you can use it to push the bearing home
Once the front bearing is fully home slide the crank out and drop it in the back and using a wooden spoon push the rear bearing gently home.
Now just put the casing to one side to cool naturally. Onto the rebuild proper. Make sure the conrod is 100% spotless. There is an old saying my lecturer taught me in college. "Cleanliness is next to godliness". So with this in mind every part we put back in this engine MUST BE SPOTLESS. I have cleaned up the gudgeon pin with the scotchbrite and the coolant holes in the piston crown I used a pin to scrape all the carbon out of. So apart from the carboniferous build up on the crown itself the piston is spotless. Go ahead and refit the rod and gudgeon pin and clips. Making sure you assemle the rod in the same direction as yoy removed it and the piston is the right way round (dont ask yes I did get it wrong. On this engine aswell LOL)
Give the piston assembly a good soaking with the light oil, to make sure the groove for the piston ring is fully lubricated and carefully refit the piston ring ensuring the gap in the ring corresponds to the locating roll pin in the ring groove on the piston. And go ahead and refit the piston assy to the crankshaft.
Hopefully in that last picture you can see the coolant holes in the piston crown I spoke about earlier. Now using some light machine oil. I personally use food grade oil, drown the piston bearings and the whole inside of the engine with oil. Go mad it doesnt matter the more lubrication the better IMO. Also spray the inside of the liner. Then with the piston at top dead centre, carefully wiggle the liner over the piston. It will suddenly pass the ring and slide down, and then just press it home locating the little cut out with the locating roll pin in the casing
Now you can refit the head. DO NOT clean the carbon off it, just make sure theres no dust or hair etc. Do the bolts up in a cross pattern a bit at a time and then refit the rear case. I also fitted a heat sink off a pumped engine, for no other reason than it looks good! LOL
OK so thats the heart of the beast done. Now for the control. The carb. Really easy this. Just remove the screw holing the barrel, the spring clips for the needles and put them safe. Then unscrew the needle assemblies 1 at a time and then you will have a stripped carb in front of you.
Now one at a time unscrew the needles from their holders and check the o rings and the wear on the needle. Any wear at all on the needle itself means it will not perform as it should, and I recomend you replace them if this is the case. DO this for the high and mid needles
Then just check the low needle barrel make sure its spotless and the o rings are fine
Finally inspect the barrel for wear and dirt, taking express care to make sure the holes are all spotless at this will affect fuel metering if any dirt is in there.
Carefully replace all the needle assemblies making sure they are tight. and slide the barrel back home and refit the location screw. I personally gave the barrel a coating in light oil too to aid its movement. I do not recommend carb cleaner at all on a model engine. The reason being is the carb cleaner leaves very fine deposits when it evaporates. This can clog the fuel ways in a model engine as the tolerences are much smaller than on a car or motorbike. Just my personal preference, but I feel its sound advice.
Now you should have a completed carb.
Go ahead now and refit the carb to the engine and thats it you have now sucessfully rebuilt a nitro methanol burning 2 stroke compression ignition engine
I hope this is a help to some people. All of the methods I have used can be applied to any size heli engine, buggy engine etc. The main thing I have to stress is the inside of the engine must be spotless. Aslong as you take your time and ensure the engine IS clean as possible. Your engine will be fine for many gallons to follow.
Kev Davies
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