leaky crankshaft

[behappy2755]

The crankshaft in my engine is leaking out the back of the engine into the pullstart at high pressures (which means I get covered in fuel and green goo from the pullstart when I pull on it). Also,at higher temperatures, air leaks back out of the rotating port under the carb, around the side of the case and back up. This in turn restricts fuel flow as the pressure pushes it back. I don't fancy paying loads of money for a new crank, might even need a new case which means it would be better just to buy a new engine. Is there a magic way to seal it with something? 

[Ziggy122]

The crankshaft in my engine is leaking out the back of the engine into the pullstart at high pressures (which means I get covered in fuel and green goo from the pullstart when I pull on it). Also,at higher temperatures, air leaks back out of the rotating port under the carb, around the side of the case and back up. This in turn restricts fuel flow as the pressure pushes it back. I don't fancy paying loads of money for a new crank, might even need a new case which means it would be better just to buy a new engine. Is there a magic way to seal it with something? 

You sir by the sounds of it sound like you need todo an engine sealing

Basically using a sealant you seal the engine up to stop air leaks and stop the fuel leak out

Make me wonder if the seals have failed on yours.... which sealing putty shud cure

But means engine stripping takes longer as you have to reseal

Ill see if I can find the guide with it on

Ziggy

Sent from my GT-I8190N using Tapatalk

[Tamiyacowboy]

 

[locky]

Crankshafts dont tend to wear out, whereas bearings and seals will. 

 

Leaking from the front is usually a sign that the front bearing needs replacing. Leaking from the back is either the exhaust gasket seal or the backplate seal.

 

If the engine runs fine then it isnt a major leak.

 

If you have the time and patience then you can remove the backplate and reseal with RTV sealant, check condition of exhaust gasket. Replacing front bearing can be done but bit more difficult.

 

Info such as the engine make/model and how old it is would be helpful, as this would determine if replacing any parts was worth it.

[behappy2755]

Its a FTX Go.18, stock from the carnage NT. All the joints are well sealed, apart from the hole in the engine back plate where the crankshaft pokes through, and the around the port under the carb (not the carb seal itself). The front bearing where the flywheel is doesn't leak. Would the sealant work in the moving parts? I'm sure it would rip off at high speed and fall into the crankcase!

[locky]

47 minutes ago, behappy2755 said:

Would the sealant work in the moving parts?

 

No cant use sealant on moving parts. There should be a shaft in the middle of the backplate onto which the one way bearing slides and then the pull start.

 

If it is leaking from around this shaft alot and it's new then take it back to the place you bought it.

 

I have no idea where you are referring to with ' around the port under the carb '. 

 

Have you checked that the back plate screws are tight?

 

Do you have an exploded engine diagram for reference? 

[Ian w]

1 hour ago, locky said:

 

No cant use sealant on moving parts. There should be a shaft in the middle of the backplate onto which the one way bearing slides and then the pull start.

 

If it is leaking from around this shaft alot and it's new then take it back to the place you bought it.

 

I have no idea where you are referring to with ' around the port under the carb '. 

 

Have you checked that the back plate screws are tight?

 

Do you have an exploded engine diagram for reference? 

 

This may help    Page 12       http://www.cmldistribution.co.uk/product/FTX5540/files/FTX-Carnage-NT-Manual.pdf

[behappy2755]

2 hours ago, locky said:

 

There should be a shaft in the middle of the backplate onto which the one way bearing slides and then the pull start.

 

Yes, this one. Its not very new, the engine has had nearly 2L through it. I have stripped it quite a few times in the past, sealing everything up properly apart from the moving parts.

 

And if you take the carb off and look down the hole, you can see the crankshaft, which opens up on the upward stroke. Then it closes and the piston goes down, and the pressure escapes around that opening on the crankshaft (which is facing down at this moment) and around the wall which holds it, up into the carb hole.

[locky]

2 hours ago, behappy2755 said:

And if you take the carb off and look down the hole, you can see the crankshaft, which opens up on the upward stroke. Then it closes and the piston goes down, and the pressure escapes around that opening on the crankshaft (which is facing down at this moment) and around the wall which holds it, up into the carb hole.

 

Now I see what your saying is what you see internally, I thought you were saying external.

 

All I can say if it runs OK then dont worry. I dont have any experience with that engine.

[Anthoop]

19 hours ago, behappy2755 said:

 

And if you take the carb off and look down the hole, you can see the crankshaft, which opens up on the upward stroke. Then it closes and the piston goes down, and the pressure escapes around that opening on the crankshaft (which is facing down at this moment) and around the wall which holds it, up into the carb hole.

When the engine is running the crank will have oil around it....this forms a seal....if the crank bearings are worn or there is excessive wear to the crank/casing and the engine does not run/tune correctly then you have an issue. Usually when a front crank bearing is worn out then plenty of fluid will leak from behind the flywheel ( but note there are also other reasons for leaks behind flywheel such as rich mixture/low rpm), when a rear crank bearing is worn out then glow plugs will blow ( again there are many other reasons why a plug may blow).

If the backplate is leaking around the shaft then it is the bushing in the backplate and/or the shaft....the shaft is steel and usually will last longer than the bush.

 

Most static checks for how an engine is sealed quite frankly are a waste of time....if it does not move...then put a tadge of RTV on it....if it moves then check that it does not have excessive freeplay and O rings/bushes are good to go.

[Tamiyacowboy]

 

only parts to wear inside the engine are the main bearings - piston and or gudeon pin, piston liner . con rod lower connection to fly wheel on crankshaft, upper connection where gudeon pin secures piston to con rod. 

the port you refer to is the intake port, by means of venturi the fuel is pulled into this port and as the crank rotates its ejected into the rear of the crank and compressed via the piston movement, as the down stroke happens the port closes off and the fuel charge is forced into the combustion chamber above the piston, on the up stroke a new charge is drawn into port and the cycles starts over again - suck - squeeze - bang - blow

fuel charge leaking from around the intake port on the crank is down to front bearing becoming loose and or worn it allows the crank to wobble and that charge you see leaking is the compressed charge from in the rear of the motor as piston strokes down. if you replace the main bearings and still find a leak from this area your crank shaft has been worn and needs replacing to. 

cheap engines are prone to leaking and wear faster than a highly named brand, some cheap engines are ok, but most are cheap for a reason they bring build cost down and add more money into the pockets of the company. a no brand .21 engine is more likely to fail before something like a nova rossi .21 , brands have a certain tollerence for there motors where cheap stuff is just cast n put together and thrown in a hobby car without much r&d at all

[behappy2755]

Yeah, I think I will buy a new engine, any suggestions?? (slide carb)

[spannermonkey]

I have a go engine in my carnage and it's a hateful thing, been nothing but trouble from day one. Given up with it and I am currently fitting a .18 SH engine. They are not a direct fit and need a custom mount. 

[behappy2755]

I have a 3D printer so a custom mount is no problem 

[Anthoop]

On ‎23‎/‎05‎/‎2016 at 14:53, Tamiyacowboy said:

 

the port you refer to is the intake port, by means of venturi the fuel is pulled into this port and as the crank rotates its ejected into the rear of the crank and compressed via the piston movement, as the down stroke happens the port closes off and the fuel charge is forced into the combustion chamber above the piston, on the up stroke a new charge is drawn into port and the cycles starts over again - suck - squeeze - bang - blow

I am nit picking ( yawn, what a surprise).

Nothing is " pulled in".......air is pushed into the carburettor and due to the venturi air speed increases drawing fuel from the jet.....the air is pushed in because the piston movement creates below atmospheric pressure in the crankcase....and so when the crank window opens, air is forced in via the pressure differential ( and if I am really picky I should say that the air expands into the area....but hey).