Head work

[zwebx]

I might start up a porting and working service for these Chinese pitbike engines
just wondering if i charged $250 for a high lift cam larger and stainless valves and port work how many people would be interested in that?

(im in Melbourne btw)

 

[my67xr]

do you have any specs on the cam/valves?
and any pics of your port work? and before/after flow sheets?

 

[zwebx]

do you have any specs on the cam/valves?
and any pics of your port work? and before/after flow sheets?

i use a 330 duration, 6.5mm lift cam, or a 280 duration 7mm lift cam and a 245 duration 6.5mm lift cam (obviously depending on how the client wants the bike to behave)

The valves are high grade stainless and the size varies as to what the person wants...
like for example i am doing my lifan 150 head to: 30mm inlet and 26 outlet because i know i can make the rest of the engine handle it whereas someone else may not want to be that aggressive.

i will post pics of my port work soon...
i will get a flow chart of my 150 head also

 

[zorro]

Hey mate, wouldn't mind picking your brains a bit on head info.
I got back into the minis by buying the kids a 110cc quad and have got an old 125cc motor I've kept from my old bikes.

For a little project I'm going to build the 125 so when the time comes to step the power up for the kids ill throw it in. I'm thinking of using a 110cc head and shaving to get the comp up (using my old school car thinking), open the valves out, fly cut the piston and put a torque grind cam in it. Is this achievable or worth using the 110cc head?

If obviously it works ill do a larger one, fiddle the carb and run it on e85.

Cheers, Ash

 

[GooseMan]

I'm glad your asking him and not me lol!

 

[zwebx]

Hey mate, wouldn't mind picking your brains a bit on head info.
I got back into the minis by buying the kids a 110cc quad and have got an old 125cc motor I've kept from my old bikes.

For a little project I'm going to build the 125 so when the time comes to step the power up for the kids ill throw it in. I'm thinking of using a 110cc head and shaving to get the comp up (using my old school car thinking), open the valves out, fly cut the piston and put a torque grind cam in it. Is this achievable or worth using the 110cc head?

If obviously it works ill do a larger one, fiddle the carb and run it on e85.

Cheers, Ash

i would recommend just upgrading engines... it would probably be cheaper and would give you alot less hassles.. why would you use the 110 head? are they the same stud pattern? are they the same dimensions of the previous head? also it may not be able to have the valves opened up anymore than it already has... because i believe the 125cc lifans and or ducars (that is what i assume you have) may not have much room

amd with raising the compression ratio shaving the head is one way to go but also a high comp piston with a raised dec height (like a pro-x piston) would do the same thing... and be cheaper but remember you are making all the tolerances tighter while doing that and you need to compensate for when things heat up and also for a little rod stretch (tends to happen on most of these engines nearing the end of there life) and then you will have to make sure you dont go too low because you will probably cause heat and rod issues (snapping them because of too much force)

all in all i would recommend if you wanted to keep your motor and make it a little faster do larger valves if they fit and a piston to suit the clearances and of cause a stage 2 high lift cam 280 duration and a 7m lift with the correct valve springs and a good port (if not just a nice cleanup of the stock ports) and changing fuels may lead to predetonation and a large hole in your pocket, i am no expert on race fuels though it could be done but to get a good benefit you do need the correct compression ratios to make everything worth while

and then you have got to make sure your clutch would be able to cope...

personally i dont think all the effort is worth doing to the smaller cc engines unless you are racing in a cc restricted class because you can go out and buy something like a lifan 150 (ripps pretty good from stock and has plenty of room for valves) or a yx 160 (not so punchy as the lifan 150 stock but they go hard when they are worked)

 

[Rodney68]

Zwebx thats sound advice you gave. I have played around with octane boosters and high octane fuels with my bikes with mixed results. I have found that these fuels work better in a higher compression engine than in a lower compression one and naturally the engine runs hotter also the higher the octane level.

 

[lets ride]

hay zwebx i have question i have a gpx 125 with a shaved 150 barrel and piston after three tanks i found it was blowing blues smoke < it had new rings as i dont normally do second hand parts > the motor had massive compression , we pulled the head off and found the cam had a flat spots , would this be because my valves were done to tight ? and we have put another new head on it and the rings were sweet but now its rattly in the head and blows a little blue smoke on start of rev any ideas

 

[zwebx]

hay zwebx i have question i have a gpx 125 with a shaved 150 barrel and piston after three tanks i found it was blowing blues smoke < it had new rings as i dont normally do second hand parts > the motor had massive compression , we pulled the head off and found the cam had a flat spots , would this be because my valves were done to tight ? and we have put another new head on it and the rings were sweet but now its rattly in the head and blows a little blue smoke on start of rev any ideas

you fellas are testin me aren't ya's
was the valves bent up when you took the head off?
did you replace the valve stem seals... and also send me a photo of the cam so i can see what you mean by flat spots?

im not sure why there is blue smoke... maybe your running a little to rich? or does it smell like oil
it may be rattly because your valve clearances are too lose... i run .004 inch inlet and .005 inch exhaust but i hear alot of other people prefer 0.006 inch exhaust

and or make sure the cam chain is tight and that thats not rattily
if its like a high pitched rattle it could possibly be pre-detonation

if you are positive it is oil being burned install a breather kit to your rocker covers because there may be too much pressure building up in there (or the bottom end because you effectively have a bigger air pump of a piston) and forcing oil from the head into the combustion chambers via the valve stem seal

and if you are testin me i will try my best not to **** up

 

[zwebx]

Zwebx thats sound advice you gave. I have played around with octane boosters and high octane fuels with my bikes with mixed results. I have found that these fuels work better in a higher compression engine than in a lower compression one and naturally the engine runs hotter also the higher the octane level.

i just run premium in my lifan 150 i find i have more torque when i run 98 i have not gone any higher compression nor higher octane...

 

[zorro]

i would recommend just upgrading engines... it would probably be cheaper and would give you alot less hassles.. why would you use the 110 head? are they the same stud pattern? are they the same dimensions of the previous head? also it may not be able to have the valves opened up anymore than it already has... because i believe the 125cc lifans and or ducars (that is what i assume you have) may not have much room

amd with raising the compression ratio shaving the head is one way to go but also a high comp piston with a raised dec height (like a pro-x piston) would do the same thing... and be cheaper but remember you are making all the tolerances tighter while doing that and you need to compensate for when things heat up and also for a little rod stretch (tends to happen on most of these engines nearing the end of there life) and then you will have to make sure you dont go too low because you will probably cause heat and rod issues (snapping them because of too much force)

all in all i would recommend if you wanted to keep your motor and make it a little faster do larger valves if they fit and a piston to suit the clearances and of cause a stage 2 high lift cam 280 duration and a 7m lift with the correct valve springs and a good port (if not just a nice cleanup of the stock ports) and changing fuels may lead to predetonation and a large hole in your pocket, i am no expert on race fuels though it could be done but to get a good benefit you do need the correct compression ratios to make everything worth while

and then you have got to make sure your clutch would be able to cope...

personally i dont think all the effort is worth doing to the smaller cc engines unless you are racing in a cc restricted class because you can go out and buy something like a lifan 150 (ripps pretty good from stock and has plenty of room for valves) or a yx 160 (not so punchy as the lifan 150 stock but they go hard when they are worked)

That's one of the answers I was looking for. To be honest I was doing some thinking and was an idea I thought could work and something to toy with in spare time, I'm over cars but still love building engines.

I might pull the head on the 125cc (both are lifan) and do some measurements. Throw a cam in it and up the comp. the e85 is not race fuel, I've tuned a couple of cars on it and its a great fuel. Cooler charge temps and higher knock threshold. Was thinking advancing the cam and a decent carb jetted right would be a bit if fun. I like pushing the norm outside the square, keeps it interesting.

 

[zorro]

Zwebx thats sound advice you gave. I have played around with octane boosters and high octane fuels with my bikes with mixed results. I have found that these fuels work better in a higher compression engine than in a lower compression one and naturally the engine runs hotter also the higher the octane level.

From what I gather you can't adjust timing so really no benefit from higher octane. Gives better burn and cleaner though. A cooler plug might help also, and richen up the mix.

 

[zwebx]

still thinking of doing somthing like this, im not sure if there would be enough numbers to make it worth while for me to invest in the tools and whatnot

 

[zwebx]

cmon, even the bigbore boys should know you can fit larger valves in the head (just aslong as its larger that 60mm bore)

 

[DHZ_XR8cing]

Most of us have engine builder's/ machine shops we already deal with.
Your best bet would be to get your bike flying and show how well your work goes.
The v2 head is already pushed close to its limit as far as valve size goes.
There would be more advantages from a correctly set up bike than looking for more power.
Most of us me included already have more power than we know what to do with.

 

[Phil67]

Zac, I will show you my piston someday, there aint anymore room in my combustion chamber trust me! The dome on my piston is that high, it is notched to allow the spark plug to fit, lol.
Damo is right, power is useless really, unless the rest of your bike, suspension, tyres, brakes etc are able to handle it. I wouldn't think any of the big bore guys keep a tyre on their bike for long, the power is just shredding them, which tells me the rear wheel is just spinning.

MAte, i will give you A head if you wanna play with it and I will trial it on my bike.

I made the "a" in capitals for obvious reasons.