Chainsaw and 2 stroke maintence

[Kram]

I was expecting the tank to be pressured but there was no hiss. I'll admit I'm unsure how a tank is supposed to deal with fuel pressure.

When I removed air filter there was visible fuel vapour in the carb entrance.

Odd that it ran on full throttle? Perhaps I knocked the L screw out of adjustment.

 

[Kram]

@dan.taylor.1 that helped, thanks! I'm not sure what fixed it, couldnt see any kink so I pulled all the hose slack into the airbox area.
I pulled the hose off the carb. Now I had drained the fuel yesterday and I didnt remove the cap. Got a good squirt peeing out everwhere as it was pressurised.

Opened cap and blow test it, flowing free enough. Pinch the hose and blow in the cap, no hissing.

Put it all back and tried to start. At first it was boggy but running a bit odd. I wound the idle back to a normal setting and now it seems to run well.

 

[angellonewolf]

ok looking at the thread

fires if fuels down the plug hole ? yes first to cheak

 

[angellonewolf]

take the fuel cap off the tank tas well o check if its not that

some times happens not often and remove the exhust as well just to rule that out as well and over the top the wire off fthe coil well

 

[Kram]

Its running perfectly now.

I have ordered this Generally seems to get good reviews but a couple of bad ones.

https://www.amazon.co.uk/dp/B07Z5VXZMD

For fitting I assume I want to coat everything in neat 2T oil.

For 4T engines I usually mix up a oil/ moly disulphide paste. Is it worth adding some MoS² to this 2T oil or just use plain 2T? Piston needle bearing just 2t oil?

I see its common to ommit the base gasket and use sealant, which requires a squish test. Worth doing?

 

[JOEPRO]

Its running perfectly now.

I have ordered this Generally seems to get good reviews but a couple of bad ones.

https://www.amazon.co.uk/dp/B07Z5VXZMD

For fitting I assume I want to coat everything in neat 2T oil.

For 4T engines I usually mix up a oil/ moly disulphide paste. Is it worth adding some MoS² to this 2T oil or just use plain 2T? Piston needle bearing just 2t oil?

I see its common to ommit the base gasket and use sealant, which requires a squish test. Worth doing?

On a 2 stroke just use 2 stroke oil as assembly lube and no need to go nuts either. It will imm burn off. For example if you added regular engine oil it will burn and may leave sticky deposits in there in a 2 stroke!

For the new kit, check the piston is a nice sliding fit with no binding or looseness either. Make sure the ring landings have 2 stroke oil in there and the rings moving freely and it should be AOK. The piston rings do take some take to bed in so I wouldn't bother compression testing it until it's got a few hours run time on it at least.

 

[DAPPH]

I was expecting the tank to be pressured but there was no hiss. I'll admit I'm unsure how a tank is supposed to deal with fuel pressure.

When I removed air filter there was visible fuel vapour in the carb entrance.

Odd that it ran on full throttle? Perhaps I knocked the L screw out of adjustment.

that's usually a sign of crank case compression ...... do a wet & dry compression test using a thick oil to confirm or rule out

 

[Kram]

that's usually a sign of crank case compression ...... do a wet & dry compression test using a thick oil to confirm or rule out

What is crank case compression, do you mean the piston rings could be leaking?

 

[DAPPH]

Yes or a score or two in the bore or a bit of wear on the bore or rings inserted upside down so they don't scrape the walls properly & seal up .
Excess fuel oil mix mist pressure builds in the crank case on firing and blows back in the carb as the piston passes the inlet port. Sometimes you'll detect a warbling sound when the machine is on full throttle and on little or no load .

 

[Kram]

The 52mm big bore kit arrived for the G372XP. I dont really know what Im looking for in terms of checking the cylinder, but the coating appears good. There are a couple of lumps inside the top of the cylinder that I imagine may cause hot spots?

I wonder if I should discard the needle bearing and buy a branded one, much like I have done with the previous spark plug.

 

[paradipiro]

The 52mm big bore kit arrived for the G372XP. I dont really know what Im looking for in terms of checking the cylinder, but the coating appears good. There are a couple of lumps inside the top of the cylinder that I imagine may cause hot spots?
View attachment 460170View attachment 460171View attachment 460172View attachment 460173View attachment 460174View attachment 460175View attachment 460176View attachment 460177View attachment 460178
I wonder if I should discard the needle bearing and buy a branded one, much like I have done with the previous spark plug.

Exactly. I would cleqn up the top of the cylinder, to be sure.

 

[dobbslc]

I'd run an oil stone round the edges of the ports too as they look a bit rough.

 

[Kram]

I am aware the nicasil coating on modern stuff is extremely thin, something like 5 microns, so any adjustments may do more harm than good?

The internal ports feel smooth to finger so I think its a trick of the light, they had been deburred before coating.

I imagine the top of the cylinder is less important as its not going to wear from the piston and most 4T cyl heads are just bare alu anyway, so I could die grind that smooth.

I didn't get a photo but the external side of the posts is a bit rough so I could do that.

 

[JOEPRO]

I imagine the top of the cylinder is less important as its not going to wear from the piston and most 4T cyl heads are just bare alu anyway, so I could die grind that smooth.

The top part of the cylinder is the most critical! That is the portion of the cylinder where the piston rings build the compression.

I would reject a new cylinder kit with obvious lumps like that and seek an alternative brand, not worth messing with it unless you got it for £5 from the slow boat from China and cannot return it.

 

[dobbslc]

I am aware the nicasil coating on modern stuff is extremely thin, something like 5 microns, so any adjustments may do more harm than good?

I mean the edges that have already been filed, there's no coating on that part anyway. They just look a bit uneven in places.

 

[Kram]

I mean the edges that have already been filed, there's no coating on that part anyway. They just look a bit uneven in places.

If you look at 5th pic the shiny silver bit is the nickle-something plated area, the dark areas are unplated. I dont think its worth modifying any of the plated bore. As it seems pretty good. However I note its not really cross hatched just circumferencial boring marks.probably adequate.

The top part of the cylinder is the most critical! That is the portion of the cylinder where the piston rings build the compression.

The roof of the cylinder has no need for the plating. It is never plated in 4T engines. There is no mechanical friction on it.

There is a colour change above the decompression port (best viewed in 3rd pic), I am unsure if this is better or worse plated.

Its an amazon, I have 30 days to do an effortless return but I cant see any obvious reasons to reject it. Obviously its a risk. New assembled engine is about £60 if I cock it up...

 

[JOEPRO]

If you look at 5th pic the shiny silver bit is the nickle-something plated area, the dark areas are unplated. I dont think its worth modifying any of the plated bore. As it seems pretty good. However I note its not really cross hatched just circumferencial boring marks.probably adequate.


The roof of the cylinder has no need for the plating. It is never plated in 4T engines. There is no mechanical friction on it.

There is a colour change above the decompression port (best viewed in 3rd pic), I am unsure if this is better or worse plated.

Its an amazon, I have 30 days to do an effortless return but I cant see any obvious reasons to reject it. Obviously its a risk. New assembled engine is about £60 if I cock it up...

I wasn't talking about the roof of the cylinder.

Your photo shows lumps on the upper edge of the cylinder wall.

So what I am saying is do not grind or do anything on that and return the cylinder as the piston rings build their compression on that upper portion of the cylinder walls

Or put blue dye on the cylinder wall and test fit the piston including rings and press fully home and verify that the rings do not cross over the defects. I would not use it without at least verifying that!

 

[dobbslc]

@JOEPRO
I see now, in picture 3 there's a blob at about 11 o'clock.

If you look at 5th pic the shiny silver bit is the nickle-something plated area, the dark areas are unplated. I dont think its worth modifying any of the plated bore. As it seems pretty good.

No don't touch the plated areas!

What I mean is the bit that's been relieved in the ports, what happens is the rings bulge out into the ports slightly as they go by so making the edges nice and smooth helps the rings last longer.
This book is worth it's weight in gold if you're messing with two strokes.

Two-Stroke Performance Tuning

The two-stroke engine has been developed to a degree that was not thought possible a few years ago. One of its virtues is that it is mechanically very simple, which is a contributing factor to its widespread use and varied application. Here, engine-tuning expert A. Graham Bell takes the reader...

www.wob.com

He also has a book on four strokes.

 

[Kram]

I wasn't talking about the roof of the cylinder.

Your photo shows lumps on the upper edge of the cylinder wall.

Im not seeing or feeling anythjng, perhaps you could circle in the photo? I will have a closer look.

 

[JOEPRO]

Im not seeing or feeling anythjng, perhaps you could circle in the photo? I will have a closer look.

Looks like something and it was described as being lumps too