Checking compression a 2 stroke

[Migmac]

I play about with chainsaws. Latest tool purchase is a compression tester. Question is throttle open or closed when testing? Done the gaztube, some say yes some say no. Will do it both ways when I get the kit to see if it makes a difference

 

[Kram]

Open allows more air in, and is how I have always done it in 4T's. You can repeat with a few drops of oil to see if it increases, hinting that the rings may be leaking - the oil will help seal them.

If you dont mind a slight offtopic, I have been watching chainsaw setup/tuning videos. It would appear a tacho is needed and most seem to be non contact types. What do you use, if you use one?

I'd like to squease some more power out of my cheap Mcculloch cs340, and next week my G372XP should arrive and may need adjustments (hopefully not!).

 

[Migmac]

Open allows more air in, and is how I have always done it in 4T's. You can repeat with a few drops of oil to see if it increases, hinting that the rings may be leaking - the oil will help seal them.

If you dont mind a slight offtopic, I have been watching chainsaw setup/tuning videos. It would appear a tacho is needed and most seem to be non contact types. What do you use, if you use one?

I'd like to squease some more power out of my cheap Mcculloch cs340, and next week my G372XP should arrive and may need adjustments (hopefully not!).

I now use one from Amazon, it’s out in the shed and I can’t remember the make. It’s peeing down but I’ll have a look tomorrow and see the make n model

 

[Migmac]

@Kram its a jayron tach I have

 

[keithski122]

I'm into my scooters and often see mention of pressure leakage testing rather than compression testing.

 

[julianthegypsy]

Open allows more air in, and is how I have always done it in 4T's. You can repeat with a few drops of oil to see if it increases, hinting that the rings may be leaking - the oil will help seal them.

If you dont mind a slight offtopic, I have been watching chainsaw setup/tuning videos. It would appear a tacho is needed and most seem to be non contact types. What do you use, if you use one?

I'd like to squease some more power out of my cheap Mcculloch cs340, and next week my G372XP should arrive and may need adjustments (hopefully not!).

Flymo used to do a really neat tacho. You put it on the end of the crankcase and it had a wire coil. You turned the knob and it released more wire. You watched the wire vibrate and at a certain point the vibration would be constant and you read the rpm off a dial. Old flymos were very fussy but that little tool made it a doddle to set them up. Cheap, cheerful and effective!

 

[Erie Fred]

Yup, leakdown tester hooked to compressed air, annual airplane inspection uses them, I've done it a few times.

 

[Migmac]

I'm into my scooters and often see mention of pressure leakage testing rather than compression testing.

Yes, I’ve seen that too. I have a wee pump and gauge coming to allow me to do that too

 

[angellonewolf]

as said on here before i do chainsaws strimmers all thed small mstuff only on a hobbie basisbeen doing for over 10 years im no expert but do get by

comp tester is a nice idea and is helpfull for a quick cheak (if not starting and fills like there is not as much compression as should be

leak down test ive got one but never used it mostly because its got a funny conector on it that ive never got round to changing mostly because if it requires a leakdown test the saw etc it needs quite a bit or work and a few parts that normaly make it not worth repairing (i dont normaly work on expensive stuff as i dont get them cheap enough)most i get are 10er 20 quidish had a few sthils huskys there the only ones that are realy worth money spending on them and as you can buy cheaper parts

tacho meter yes only a cheap and chearfull one was a 10er ish and does well not that i ever use it to get a bit more out of the units just to make shore its running as standard specs (quick goole cheak will give you the rpms of most mechines

i think not that ive cheaked putting the saws etc up to the max allow rpms stresses the engines more and the little you get out of it

 

[Migmac]

as said on here before i do chainsaws strimmers all thed small mstuff only on a hobbie basisbeen doing for over 10 years im no expert but do get by

comp tester is a nice idea and is helpfull for a quick cheak (if not starting and fills like there is not as much compression as should be

leak down test ive got one but never used it mostly because its got a funny conector on it that ive never got round to changing mostly because if it requires a leakdown test the saw etc it needs quite a bit or work and a few parts that normaly make it not worth repairing (i dont normaly work on expensive stuff as i dont get them cheap enough)most i get are 10er 20 quidish had a few sthils huskys there the only ones that are realy worth money spending on them and as you can buy cheaper parts

tacho meter yes only a cheap and chearfull one was a 10er ish and does well not that i ever use it to get a bit more out of the units just to make shore its running as standard specs (quick goole cheak will give you the rpms of most mechines

i think not that ive cheaked putting the saws etc up to the max allow rpms stresses the engines more and the little you get out of it

I work on my own stuff or close friends. Nobody else’s stuff yet. Keep looking on Facebook market place for saws but the majority of them are going for strong money. No meat on the bone for me

 

[8ob]

You can pretty much assess a chainsaws compression the second you pull the starter cord, don't think I have ever tested one with a gauge. Ring tension is more important than ring gap.

Bob

 

[angellonewolf]

I work on my own stuff or close friends. Nobody else’s stuff yet. Keep looking on Facebook market place for saws but the majority of them are going for strong money. No meat on the bone for me

same here now i only ever done it as a hobbie to get in play time ive never had a few grand classic car that needs doing up etc so small petrel stuff was a cheap way of playing for little money was never going to get rich from it

most chainsaws fetch around 35 45 quid if a cheapy working sthil 80 to 100 ish husky run of the mill saws around the same
strimmers working cheapy stuff 30 to 40 named stuff echo tanka 60 husky sthil 60 to 80

so not going to make any money as cash up front to buy non working buy 8 over a period for say 120 quid add every one cost a few quid in fuel, carb cleaner spark plugs etc then 3 are not worth reparing (remove spark plugs bulbs etc for spares) so fix up the other 5
sell a echo for 60 the other 4 for 35 each thats 200 so only make 80 quid

this does vary but as said was never for a profit thing just used to keep me busy and i liked the play time with no cost to me

now as your self mostly a few repairs for work and a few mates keeps my hand in and same dont cost me any thing but time but realy trying to slow that down as got other stuff on the go and having small projects on the go seams to keep me getting on with the bigger stuff

 

[zzr1200]

Compression gauge requires open throttle and fast pulls on the starter cord, a pressure/vac test tells more about the engines ability to run, imo...

You can always see the piston/cylinder wall condition via the exhaust port....generally quicker than doing a compression test...

 

[Migmac]

You can pretty much assess a chainsaws compression the second you pull the starter cord, don't think I have ever tested one with a gauge. Ring tension is more important than ring gap.

Bob

That’s my normal way and thumb over the plug hole

 

[angellonewolf]

Compression gauge requires open throttle and fast pulls on the starter cord, a pressure/vac test tells more about the engines ability to run, imo...

You can always see the piston/cylinder wall condition via the exhaust port....generally quicker than doing a compression...

hows that yea looking at the bore through the exhaust port normaly tells you more but most have never been removed in there life 2 bolts that may snap if removed (never had it happen to me but so say does happen) and a lot of them have metal bent over to stop vibration unscrewing them
a compression test is remove the spark plug (thats normaly under the rear cover that unclips or one screw to remove )and push on the tester id think id do that first perhaps thats just me

but pulling the cord will give you the first idea if its down on compression or opsite if realy hard to pull somthing wrong with a seized pistion

did get caughtout years ago when i first started as there was an easy start mech on the pull chord system that seam to make it easy to pull

 

[Morrisman]

Yup, leakdown tester hooked to compressed air, annual airplane inspection uses them, I've done it a few times.

I made my own when trying to find an elusive misfire on a V8 once. A cobbled together concoction of fittings, a gauge, a ball valve etc. Not my finest work but it did the trick with what I had to hand.

And oddly enough the misfire disappeared after I'd deduced there was nothing wrong with the suspect cylinder...

 

[Dozzer]

Leak down only tells you if the cylinder & Rings are making a seal at TDC or BDC on 4 stroke, but you need to lock crank, and you can only check a 2 stroke at TDC, Comp test should always be done full throttle and few rotations, as you are looking for some crank case charging on most 2 strokes.
have seen a few Rotax 912's with scores down boars but passed leak check, its part of rotax training but i dont agree with it.
Just finished doing 200hr servicing a rotax 582 for my hangliding club.

 

[Erie Fred]

You can check the leakage anywhere you want by moving the crank.
On the air-o-planes, we moved the prop...carefully.
On 4 strokes it's good to use to find if the valves, which one, rings (listen at the breather, then go add a teaspoon
of oil to that cylinder and repeat) etc.

 

[Dozzer]

You can check the leakage anywhere you want by moving the crank.
On the air-o-planes, we moved the prop...carefully.
On 4 strokes it's good to use to find if the valves, which one, rings (listen at the breather, then go add a teaspoon
of oil to that cylinder and repeat) etc.

Lycoming or Continental? On the rotax engines there are lock pins for TDC , as when you start pressuring cylinders @ 6bar things move.
For leak check engine should be min of 50-70deg C.
Most have a caveat if a pressure decay is unclear use a comp check!!