Post by adam2 on Mar 20, 2021 12:09:15 GMT -5
I have a 1P57QMJ engine (short case, with EGR, 4 bolt pattern) that needs new crank shaft, cylinder head and piston, valve block and valves.
It’s hard to find parts for the P engine, apparently I can use rebuild kits non-P engine so long as I match things (and understood I’ll lose a little power going away from the P engine). The P engine has a taller head than the non-P engine.
If I use non-P versions, I think I need to get a new timing chain and new cam (A9 cam seems to be recommended). Is that right? Anything else I need to change?
I’ve never rebuilt an engine before, so don’t assume I know too much!!! I did take this one apart.
Here’s info I’ve found on the P vs non-P version of the 157QMJ, if it helps.
The P series engines have a taller head, longer timing chain, & different valves/seats that give it slightly more performance than the other GY6's. They also use a different CDI. Maybe 1.2, 1.5, or 2 hp more power. Cam is probably different.
Hello, c1ian here I have a roketa 150 with the 1p57qmj and i have been using the 157qmj cylinder kit successfully for over 2 years. The difference is in the depth of the reccess for the cam it's shallower. It wont accomadate an oversize cam. In my experience as long as the cylinder jug and head are both replaced with that of the 157QMJ, and no bigger than a A9 cam is used everything is copacetic. I used an A10 and had to deepen the valve reccesses on the piston just a hair to prevent slapping. I put modeling clay in the recesses, torqued down the head and gently turned it over by hand once. Then removed the head checked the clay to see if valves had pushed through to piston they had slightly so deepened them repeated process and it was good. Next engine I used An A9 and no problems or modification needed. Hope the info can help someone or atleast save some time. Oh and these swaps were both on the 4 bolt version. It is to the best of my knowledge the two bolts even though stamped gy6 are referred to as gy7, and also have 1P57 and 157 versions.
If you have 28mm intake and 23 exhaust valves, you have the "large valve" head regardless of which head you have.
As far as cams, "P" engines use a large base circle cam and 157's have a smaller base circle. the cams are interchangeable, but you must use the correct rocker arms for the cam you are using. You can't adjust "P" rockers enough to ride on a small base circle cam and vis-a-versa.
As far as spring binding, I have yet to experience this with a cam swap, but that doesn't mean it can't happen. I just haven't hit the right combo for spring binding.
These heads are both 60mm heads if you have a 70mm head its a different head all together. Now i have since measured and timing is not affected enough to cause problems and i have also noticed that 157qmj and 1p57qmj heads are mostly the same but vary casting to casting so these kit you find everywhere for the 157qmj will work on the 1p57qmj as long as you have 60mm head. Also you must check and make sure the cam you select wont bottom out you springs remember these heads are made by several different companies and they are all slightly different but are supposed to work. If you head is 60mm measured from the head surface to valve cover surface you are fine. Also if you have heard that the cam will not work on the 1p57qmj head, remember that if you order a whole kit with head for a 157qmj for your 1p57qmj with 60mm head that there should be no problem because your using a 157qmj head .
It’s hard to find parts for the P engine, apparently I can use rebuild kits non-P engine so long as I match things (and understood I’ll lose a little power going away from the P engine). The P engine has a taller head than the non-P engine.
If I use non-P versions, I think I need to get a new timing chain and new cam (A9 cam seems to be recommended). Is that right? Anything else I need to change?
I’ve never rebuilt an engine before, so don’t assume I know too much!!! I did take this one apart.
Here’s info I’ve found on the P vs non-P version of the 157QMJ, if it helps.
The P series engines have a taller head, longer timing chain, & different valves/seats that give it slightly more performance than the other GY6's. They also use a different CDI. Maybe 1.2, 1.5, or 2 hp more power. Cam is probably different.
Hello, c1ian here I have a roketa 150 with the 1p57qmj and i have been using the 157qmj cylinder kit successfully for over 2 years. The difference is in the depth of the reccess for the cam it's shallower. It wont accomadate an oversize cam. In my experience as long as the cylinder jug and head are both replaced with that of the 157QMJ, and no bigger than a A9 cam is used everything is copacetic. I used an A10 and had to deepen the valve reccesses on the piston just a hair to prevent slapping. I put modeling clay in the recesses, torqued down the head and gently turned it over by hand once. Then removed the head checked the clay to see if valves had pushed through to piston they had slightly so deepened them repeated process and it was good. Next engine I used An A9 and no problems or modification needed. Hope the info can help someone or atleast save some time. Oh and these swaps were both on the 4 bolt version. It is to the best of my knowledge the two bolts even though stamped gy6 are referred to as gy7, and also have 1P57 and 157 versions.
If you have 28mm intake and 23 exhaust valves, you have the "large valve" head regardless of which head you have.
As far as cams, "P" engines use a large base circle cam and 157's have a smaller base circle. the cams are interchangeable, but you must use the correct rocker arms for the cam you are using. You can't adjust "P" rockers enough to ride on a small base circle cam and vis-a-versa.
As far as spring binding, I have yet to experience this with a cam swap, but that doesn't mean it can't happen. I just haven't hit the right combo for spring binding.
These heads are both 60mm heads if you have a 70mm head its a different head all together. Now i have since measured and timing is not affected enough to cause problems and i have also noticed that 157qmj and 1p57qmj heads are mostly the same but vary casting to casting so these kit you find everywhere for the 157qmj will work on the 1p57qmj as long as you have 60mm head. Also you must check and make sure the cam you select wont bottom out you springs remember these heads are made by several different companies and they are all slightly different but are supposed to work. If you head is 60mm measured from the head surface to valve cover surface you are fine. Also if you have heard that the cam will not work on the 1p57qmj head, remember that if you order a whole kit with head for a 157qmj for your 1p57qmj with 60mm head that there should be no problem because your using a 157qmj head .
