engine diff between 125 and 150 cc - ? By godfeast (Read 2,191 times)

[godfeast]

I have one final question I cant seem to get anyone to answer for me.

I bought an ebay 150cc engine from tmotorsports, which came marked as a 50cc on the engine casing, but the form factor is a long 150cc case with top mounting bolts.

I am told that in a worse case scenario it cannot be less than a 125 (and in that case the coding is way off and seller admits it, but thats another story).

The engine is in and runs in my sunl adventure 150cc scooter.

I put it in yesterday and on first run around the neighborhood, it sounds kinda loud (maybe incorrect exhaust gasket or loose valves - maybe combo of two) but it also only gets up to about 40 then crawls up to 45 and wont go any faster.

My old 150cc right after a top end rebuild would get up to 60-62mph no problem right off the bat, so I'm concerned.

I havent had a chance to really go over it , but it might be crazy light rollers as well, or maybe a jetting issue - no idea atm.

My main concern and question is: If I did get stuck with a 125cc engine, how much work is going to be needed to make it 150cc?

Is it just a top end job replacing the sleeve, piston, and rings? Does the head need changed? Valves? Crank? Carb?

How can I tell for sure if its a 125cc if the engine castings are marked incorrectly? Can I only tell be removing the head and checking piston size?

Any help or ideas would be appreciated.

[Cruiser]

Here's a good tutorial on identifying the size of your engine:

scooterdoc.proboards.com/index.cgi?board=engine&action=display&thread=256

Engine mounts for 50cc and 150cc are different and would require extensive mods to get a 50cc to fit in a 150cc and vice versa. I don't know the setup for a 125cc, but it probably would be similar to the 150cc.

[godfeast]

The whole problem originates from the manufacturer mismarking the case on purpose.

The only solid thing I have to go on is the fact that the case is identical to a 150cc long and fits in the same scooter as one - which would have me believe that I have a 150cc, except I've been told that a 125cc is also made in this type of case.

I need to be able to tell by physical examination of a part to tell what type I have. I just dont know what to look for or if I find out I have a 125cc, what I need to do to make it a 150cc properly.

I appreciate the link, but standard, this is your engine if its stamped this way, just doesnt help if its mis-stamped by the people who made it.

[Alleyoop]

Maybe the size of the Carb, on the 150s they come with a 24MM Carb.
I have heard that a 150 is actually a bored out 125.
Alleyoop

[sprocket]

If it says 149cm3 on the cylinder casting it is 150cc...but this gray market stuff who knows...

The only REAL way to tell is to pull the head and measure the piston...

[Kaveman]

engine type markings ? That can be found underneath on left crankcase below where the variaitor / transmission cover is, Should be marked like 152qmi or 157qmj . 152qmi is 125cc , 157qmj is 150cc . The 2 are pretty much the same mechanicaly but with different cylinders and piston sizes.
Bill C.

[sprocket]

Ya Bill... These are replacement engines. They came into the US as 50cc and are marked that way...but they sell them as 150cc. Some people say they are 125cc but I don't know for certain...I think the are really 150ccs

This has been going on for the past year...grey market Ebay stuff...

[Alleyoop]

In other words brought over on the SLY undercover of night.
And when you get it you Don't know what to do

[godfeast]

Well, I'm feeling like it has to be a 150cc.

I put on my old uni filter and upgraded the carb with my old main jet (102 on new stock to my 114), as well as, raising the carb needle one notch from the 2nd to 3rd position.

The scoot is now on roughly 60 miles and does about 53mph, up from 45 when first put out on the road completely stock.

It was that 45 mph sustained top end ceiling that had me worried, but now as little tweaks have put it past 50mph, Im not so concerned, all though I suppose theres still a chance.

Im checking valve clearance tomorrow. If I had a spare gasket, I'd just pull the head and look while I was in there; may grab one later this month and do it anyways.

[sprocket]

You are probably running very rich... check your plug... going from 102 to 114 is massive and you probably don't need the throttle needle adjustment...

The valve cover gaskets are O-rings they are reusable... Adjust the valves after the scooter has sat overnight...it must be cold

Break the engine in first before making all theses adjustments...

[godfeast]

gasket in question was the head gasket - I dont have a spare. I usually replace the valve cover gasket with rtv since I don't like that garbage strip they put on them.

I may go ahead and move the throttle needle back down then; wasn't sure how rich I needed to make it since it obviously wasnt running correct with the uni on and being new. I did adjust the air mix screw until it sounded right - est about 3-3.5 turns from completely in; sounded pretty good though.

The engine should be right around 115 miles after tonight's commute.

I can wait on valve adjustment; at about what point do you feel would be appropriate though?

I have read several different ideas on what mileage ends the "break in" period.

Monday the miles should be at or around 250ish and by next weekend it should be well over 500.

[sprocket]

Break in mileage really depends on how you do it and who is the 'expert'. Generally if you are accelerating and de-accelerating under load 125-150 miles should be enough to seat the rings and bearings with regular oil.

The valves usually don't need to be touched until about 700 miles

Why are you taking the head off? If you do, you should spray the new gasket with copper gasket compound and be certain to correctly torque the head bolts in a criss-cross pattern...

Frankly if it is just to see what sized piston is in it ...I wouldn't bother..what difference is it going to make?

You could screw something up big time...

[godfeast]

I have rebuilt a top end on the previous engine, so its not like I'm unfamiliar with the procedure to take a head off.

I just have a need to know if what i bought is what I got.

i was worried about the valves because I know that new engine's frequently need them adjusted as they loosen up after they get heated the first few rides; is this not the experience you have had with gy6's?

[Alleyoop]

I think you have a 150 due to the mph, the mph you are getting is what most 150 are capable of stock.
Alleyoop

[godfeast]

BTW, still looking for a definite answer as to what changes on a 125cc to make it a 150cc.

Is it really just the top end and with 125cc's having to be re-bored to accept a 150cc sleeve?