157QMJ to 1P57QMJ engine swap: is it possible?

I KNEW you would be one of the the first to respond .....you are extremely helpful to many people on here...thanks for that.


I was just thinking of a possible project over the winter.

It should bolt right up, and you can always take the stator & magneto out of your current motor

I wonder if I swapped them out...would I feel the 1 to 1.5hp difference??...if thats even a true figure.

Ahh..if the engine mounts match and the stator matches then it's 4 bolts to swap an engine.

technically yes this is true but there are other things involved.

whats your point?

If you can get a full engine that works fine, I would definitely make the trade with your friend. You will now have a backup engine with all the parts. Which one you use first will probably not make much difference, but you never know until you run it. By making the trade, all the parts that you may have to replace at some point, will be at your finger tips. Plus, you save a lot of money and waiting time. I have done this before (actually twice) and the swap was not difficult, if you decide to go that way. But, you should definitely make the trade, no matter which engine you use after the trade. Here is my thread when I installed a new engines: scootdawg.proboards59.com/index.cgi?board=talk&action=display&thread=11305

If you measure carefully (as Jake318 suggested above); I think you'll find that the P engine is taller from the deck on the engine case to the top of the cylinder head. I think most, if not all, of this height difference is in the P cylinder head (taller head, smoother port entries, possibly larger valves as well). In theory, you could swap the cylinder, cylinder studs (longer on P motor) and cylinder head from the P engine onto your current engine and get a performance gain from the improved head. However, as Harry noted, it only takes 4 bolts to drop the engine and swing arm assembly and pull the entire motor.

My opinion is that the P swap would generate a noticeable power increase because of the increased airflow of the P head. The bolt on changes you have already made (exhaust, intake, re-jetting) will further compliment the increased airflow of the P head.

If I had a P motor lying around, I'd take the upcoming winter to pull the head, get the spring seats machined deeper to support a high lift cam (a machine shop will do this for a modest charge), do a simple port cleanup with a dremel/die grinder, install & degree in a new high lift, modest overlap cam (stock cam was about zero overlap), verify piston to valve clearances and then swap the modded P motor into the scoot in time for spring riding.

YMMV,

Mitch

Since this is 3 years old I was wondering if there was any more info out there

I too have a 157QMJ motor, and I am looking at putting in a new "P" engine.

Does it indeed just drop right in?

Are the electrics different?

Exhaust location, use the same Carb etc

I get that the head is taller etc

But the question is, will it fit in my scooter? And will the electronics be compatible?

Thanks Sprocket

My current is a 12 pole

So I guess we'll see. I'm really struggling with this decision

Part of me wants to fix this engine, but I just cant figure out the whirring noise

Part of me wants to start from scratch, do a proper break-in, put on a prodigy variator,UNI, new jets, my exhaust, then LEAVE IT ALONE.

I really don't want to take my engine apart anymore.

Thanks for the info Sprocket. I just got me a 1P57QMJ engine brand new with a cracked rear case damaged in shipping on a new trike. Got it off eBay for $75 shipped. My current engine have leaky valve seals and piston rings so I am going to buy a new case half for the broken part and stick this bad little sucker in my scooter. I will mos def take care in seeing what stater I have and plan accordingly. I have a lot of free time so this sounding like a lot of work for little return just doesn't matter with me. Can you think of something I may be missing?

I was just going to spend $150 to fix the oil burning issue to bring it back to stock to sell it. Now I may keep it if it goes better than my stock engine.

Picture of the new motor

the broken piece is the shock mount, at least on mine.

You could just find a way to use the other shock mount.

No don't try it, there were some 150cc single shock scooters made, but thankfully they stopped making them. The single shock attacked to the engine anyway like on the 50ccs

Should be easy to fabricate a bracket to the other mount...and just weld it to the case...


Here is a Vespa but you get the idea

motorcycles.about.com/od/newbikephotogalleries/ig/2008-Vespa-S-150-Scooter/Four-Way-Adjustable-Preload.htm