I think I just messed up...
- Thread starter timmmy
- Start date
Valve guides are brittle, so there's virtually no chance of distorting one to a point it cannot be safely removed. They'll shatter first, which might make the removal a little more difficult and that's about the worst possibility. As long as you've not seriously hurt the aluminum head casting, the head should be fine. R&Ring valve guides isn't especially difficult, or tricky. It does require special drivers, a finish reamer, and a modestly skillful touch.
timmmy
Member
Thanks guys...You are making me feel better about this but still some questions. So are these things made to be removed? The reason I ask is I want to powder coat the head. The guides have a rubber gasket and they would never withstand the 400 degree 15 minute bake cycle. If they can be removed I could buy a used head and switch these out after I coat the old head I have. Even if I want to buy new ones I get very little results, and are the exhaust and intake guide different specs?
What do ya'll think?
What do ya'll think?
kirrbby
Well-Known Member
The seals (valve stem seals) are just little caps that pop onto the valve guides. They're about ⅜" diameter and ¼ high. They should come off if you pry up with a screwdriver or pull up with a hook.
The valve guides are different, in & ex (I think). They are made to be replaced. But are probably OK to leave in for powder....so long as you're not coating the INSIDE of the head.
The valve guides are different, in & ex (I think). They are made to be replaced. But are probably OK to leave in for powder....so long as you're not coating the INSIDE of the head.
timmmy
Member
Kirrbby, Not coating the inside of the head but the process requires baking at 400 degrees for 15 minutes. Its the green rubber gasket under the guide that I am worried about melting. Now since its green (not black) do you think its a high temp rubber gasket? I dont know...?
Another question, if I buy a new used head, could I put a 70cc head on top of the 88cc bore kit on top of a 50cc bottom end or would the piston rod be an issue on its length?
Another question, if I buy a new used head, could I put a 70cc head on top of the 88cc bore kit on top of a 50cc bottom end or would the piston rod be an issue on its length?
Houredout401
Active Member
Powder coat on a head is not something I would recommend for an air cooled bike, but is this what some people do on these little bikes? PC melts around 400 degrees, so maybe the head does not get that hot, but PC will definitely hurt heat dissipation and contribute to overheating.
kirrbby
Well-Known Member
Ah ya, there are some o-rings or something under there.
Yes a 70 head would be much better for a 88. The z trans is the same as the 70 of the same year. One thing tho is apparently the clutch in the 50 is not great. Better to get a clutch from a 70.
Your 97 would be considered a "short rod, long stroke" pretty sure. So you would need to pick your new head... Then buy a "long rod short stroke" piston... With a dome to match the combustion chamber of whatever head you're using. DRATV has a page that spells out the differences between different rods and heads etc.
Not many would recommend coating a head. I'm sure it's been done. You'll want to really watch the heat, especially during the break in.
kirrbby
Well-Known Member
http://dratv.com/infoonfitment.html
--- DRATV says long rod, for your motor. Stroke length doesn't change. So you would buy your BB kit for a long rod crank....with a long rod piston with dome to match the head you use.
--- DRATV says long rod, for your motor. Stroke length doesn't change. So you would buy your BB kit for a long rod crank....with a long rod piston with dome to match the head you use.
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fatcaaat
Well-Known Member
I guess I'll chime in with two positions.
1. I would not suggest PC the head or cylinder. It will retain heat. Ok for the covers and cases. You can purchase vht header or engine paint and since you were going to PC it, then go ahead and blast as you were planning and paint it with vht and then bake it at 250 for an hour or so. I have an old propane grill I use to cook things like this. Once cooked, it is nearly as tough as powder and also impervious to pretty much any shop fluid.
2. Generally speaking the guides on these things never wear out. But now that you knocked one out, you do need to use special tools or you'll foul them up going in or out. Dratv sells what youo need in terms of removal/installation tool. You'll also want a reamer if you are messing with them. Also, I don't think it is vitally important for you to use a stock oring when you put it back in...but a heat resistant viton ring in the same dimensions will work fine as that's what I have used without issue.
1. I would not suggest PC the head or cylinder. It will retain heat. Ok for the covers and cases. You can purchase vht header or engine paint and since you were going to PC it, then go ahead and blast as you were planning and paint it with vht and then bake it at 250 for an hour or so. I have an old propane grill I use to cook things like this. Once cooked, it is nearly as tough as powder and also impervious to pretty much any shop fluid.
2. Generally speaking the guides on these things never wear out. But now that you knocked one out, you do need to use special tools or you'll foul them up going in or out. Dratv sells what youo need in terms of removal/installation tool. You'll also want a reamer if you are messing with them. Also, I don't think it is vitally important for you to use a stock oring when you put it back in...but a heat resistant viton ring in the same dimensions will work fine as that's what I have used without issue.
timmmy
Member
O.K. Powder coat is out! I didn't even think of the temp issue but looks kike it would be. On to this 70 vs 50 head.
My thinking here was I could get larger vales and a larger intake port/valve with a 70 head...That should be right?
I have the 88cc kit already as noted below.
As Kirrbby noted the rod length, which worries me if I can talented enough to determine with accuracy the measured length from the info he sent me. It does have some markings that I will research.
49cc = 39mm bore x 41.4mm stroke (C50, Z50, Jincheng 50)
72cc = 47mm bore x 41.4mm stroke (C70)
These look the same
49cc 12v head.(small valves GK4 head)
My head size (hence larger head)
How do I know what piston size I have?
What looks right and what looks wrong about what I am trying to do here?
Thanks!!
My thinking here was I could get larger vales and a larger intake port/valve with a 70 head...That should be right?
I have the 88cc kit already as noted below.
As Kirrbby noted the rod length, which worries me if I can talented enough to determine with accuracy the measured length from the info he sent me. It does have some markings that I will research.
49cc = 39mm bore x 41.4mm stroke (C50, Z50, Jincheng 50)
72cc = 47mm bore x 41.4mm stroke (C70)
These look the same
49cc 12v head.(small valves GK4 head)
My head size (hence larger head)
How do I know what piston size I have?
What looks right and what looks wrong about what I am trying to do here?
Thanks!!
PC isn't a great choice for any engine pieces. Heat retention is a real concern...so is heat, like around the exhaust port. The outer covers are sure to get scratched & nicked along the way. PC is NOT refinisher-friendly. And when it comes to touch-ups...fuhggeddaboudit!!
Rod length has no bearing on stroke length. It does have to be matched to piston compression height, i.e. the distance from the wrist pin to the piston crown, as measured at the top of the compression ring land. The 6v motors had shorter rod length; using a 12v (long rod) piston with a 6v (short rod) crank assembly would leave the piston way down in the bore (negative deck height), leaving the combustion chamber without a squish band and the motor with pathetically low compression. Using a 6v piston with a 12v crank assembly would leave the piston above the deck at TDC...no need to worry about compression ratio, it'd hit the head.
FYI, rod/stroke ratio affects the shape of an engines power band. The longer the rod, the higher (numerically) the R/S ratio and the higher the rpm limits.
Any of the 72cc heads will have larger ports & valves, definitely better breathing than a 49cc head. The 72cc heads have larger combustion chambers than the 49cc flavor. Thus, the piston type should be matched, to maintain CR. Again, of the possible mismatches, one will give low compression, the other mechanical interference.
Rod length has no bearing on stroke length. It does have to be matched to piston compression height, i.e. the distance from the wrist pin to the piston crown, as measured at the top of the compression ring land. The 6v motors had shorter rod length; using a 12v (long rod) piston with a 6v (short rod) crank assembly would leave the piston way down in the bore (negative deck height), leaving the combustion chamber without a squish band and the motor with pathetically low compression. Using a 6v piston with a 12v crank assembly would leave the piston above the deck at TDC...no need to worry about compression ratio, it'd hit the head.
FYI, rod/stroke ratio affects the shape of an engines power band. The longer the rod, the higher (numerically) the R/S ratio and the higher the rpm limits.
Any of the 72cc heads will have larger ports & valves, definitely better breathing than a 49cc head. The 72cc heads have larger combustion chambers than the 49cc flavor. Thus, the piston type should be matched, to maintain CR. Again, of the possible mismatches, one will give low compression, the other mechanical interference.