What is a good compression ?

I want to know, what is a good compression ???

90,100,120 ???

Re: What is a good compression ?

really good compression is 180 psi, good compression is 150, ok compression is 120, bad compression is 90, just enough to ignite the fuel is 90, shit crap compression is 70 and dont try to make it run.

Re: What is a good compression ?

thats odd, because my Tomos' compression is 95psi & it runs great, i guess it just depends on the type of engine.


Re: What is a good compression ?

What is ... "runs great "???

What is your 0 to 25 time ?... your top speed ?

95 ain't shit... its low... I told you that.

(it has to be checked right though... checking it wrong will give a low reading)

And is that 95 AFTER you shaved the head or not ?

Re: What is a good compression ?

how can you check the psi?

What is the "right" way to check compres

Hi Fred:

Just curious, what is the correct way to check compression? I have one of those pressure gauges that screw in to the spark plug hole. I pedal real hard and then read the measurement. Is there something else I should be doing?



Re: What is the "right" way to check com

im doin the same thing with the screw in guage, and my reading comes up between 95-100psi, if thats wicked low ill shave my cylinder head till i get around 120. if im doing somthing wrong let me know. i screw the guage in a little past finger tight so it dosent bind in the spark plug hole, then back pedal (2 speed bike) till the reading on the guage wont go any higher.


garret garret garret

You don't just ... 'keep shaving the head till you get good readings"

There is a REASON for low readings... and it is the condition of the cylinder and rings... (providing the head gasket seal is good)

You have already described a seizure and aluminum deposited on the bore and your brake hone honing process... and then asked if there was a chance it wasn't that great and maybe you should have it redone with a new bore...

then you rejected my answer as being wrong... 'because you KNOW the bore is good"... ?


if your bore isn't worn too big... a simple professional hone job and new rings would bring you right back up... that is probably only $20 or so.. ??

... if you do the head very much farther.. eventually it will hit the piston...

Do the right fix to the right part....

the "right" way

Chris... All I really meant was to open the throttle while doing the test.

Thats real important with a 4 stroke... not as important with a 2 stroke.. but it can still have some effect.

(the open exhaust port will still let most of the necessary air in)

Thats all... on a 4 stroke.. since there is no where for air to get in other than the carb... a closed throttle will give real low readings.

by the way.. all the times I said .. "the roller weights shouldn't be heavier for the PA's"... I believe I always said.. "for the PA50I's"... since I have figured the outer ramp plate for the II's has a steeper ramp... heavier weights might have a good effect for traveling all the way out... dunno

But if your weights go all the way out at their stock weights.. then heavier weights won't help.

I will find out in one week or so.. I have a II motor coming in.. with the variator on it... (has 68 supposed miles on it )

I'll see then... the I really is geared all wrong.. low range is too tall... and yet it also shifts much soon.

If I started with lower gearing and could let it rev in the low range some.. It would kill its current 0 to 25 time.

im sorry, ill go get it honed

i DID get a new piston and rings, and a new cylinder, but that damned tap broke off in one of the muffler bolt holes in that cylinder, so i switched back to the old one. now i KNOW your right, where should i go to have it done? the local 'ped shop charges ridiculous labor rates (prolly cost 40 bucks to have that cylinder honed) thats why i tried doin it myself, their also crooks, they wanted 1100 for a new tomos sprint! i could get one for like $995 online, or a targa LX for that same price. since i used a brake hone, could i take it to a brake place (i.e. mineke) theres one really close to here. I'll definitely get new rings from the moped junkyard. i could TRY taking it to the local motorcycle shop (who can order tomos parts, and work on the bikes, so they might do it) but i dunno, where do you think i should go?



hey don't be sorry... I like people who stand their ground.

We can argue and still be friends.

But.. where to go ?

I don't know... but the problem you have with motorcycle shops is... many don't have the smaller tooling for small bores... some stop at about 50mm

Some do... some don't.

Here .. they only charge $40 for a Bore AND hone... so $40 for a hone is ridiculous... it takes 5 minutes even with a pro power hone.

Measure your bore FIRST... then get out the phone book and call several and ask them ... "Can you hone a 40mm cylinder" ?

Specify JUST a hone (for now).

Don't even say "moped"... if they say "whats this for? (over the phone).. say "its a 40mm cast iron cylinder... 50cc"... (thats all they really need to know.. if you say 'moped' they might just say No)

Later when you get there.. you can tell them the correct bike... if they even ask..


You oughta get that tap extracted from that new cylinder !

Look in the phone book under 'tap extraction'... or machine shops.

Call tham and tell them you have a 6mm tap broke off in a small cast iron cylinder.

Maybe $20 to get that out.

ill get that tap extracted

that cylinder has maybe 200km on it (according to my psuedo mph CEV speedo whose odo is in kilometers) its in nice shape except for that damn stuck tap. I'll also try holding the throttle OPEN while kicking it over, i bet it will make a difference. there IS a machine shop down the street from me their sign says "precision CNC machining" do you think they would be able to get that tap out? their SO close (like close enough to ride the ped to with the to-be-repaired cylinder in a bag bungeed to the rear rack) im gonna give it a try, i have a feeling it may be the wrong type of shop though.


Re: ill get that tap extracted

try them.. walk in the 'trucking door' to the shop.. don't go in the front door.

See if you see a guy standing next to a running machine.. walk up to him and ask them if they can do that... (carry the part with you).

If you're lucky...he might do it for you while his machine runs.

or he might tell you no..

.. ask if he knows who extracts their broken taps... (CNC places break taps off every once in a while... they either do it themselves... or send them somewhere to get it done)

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