Post by 90GTVert on Apr 13, 2016 20:48:18 GMT -5
I didn't do much with the engine today. I did check squish clearance. I was curious to see if the squish would be super tight like the P2V clearance. I taped solder on in 4 spots to measure.
It didn't get squished nearly as bad as I expected. It was about 0.040" to 0.050". Most motorcycle info says to look for 0.035". I was hoping maybe it would be very tight, so then I could come up with a thin gasket and have a squish clearance near that spec and be closer to a reasonable P2V clearance.
At that point, my thought was that I may see what I could do with a few degrees of camshaft advance. How to do that though? Oh right, I ordered this adjustable cam gear since the BBK seller carried it as well.
The stock cam had a couple of markings, but I made new ones that aligned with the lines and holes used to ID proper TDC to make it a little easier to get it near it's original timing when the new gear goes on.
I pressed the old gear off and bent the gear. I've only messed with one other cam gear, and it did not take the amount of force to remove the gear that this one did. As long as the adjustable gear isn't junk, it shouldn't matter.
I centered the cam sprocket the best I could in it's grooves and so the top hole aligned, and made marks where the two side holes are so I'd be able to see them when the cam gear is apart.
I heated the section of the new gear that I needed to press on and aligned it the best I could. Then I pressed it on. When I started getting near where I thought it may need to sit, I kept installing the cam to see how the alignment was with the chain and guides. I probably should have just measured my stock cam or compared to that, but I didn't even think of it at the time. I ended up with the gear almost as far as it would go on and alignment looked good.
My plan was to see what a little advance would do for P2V clearance tomorrow. Obviously any reasonable amount isn't going to solve 0.002" (if that) on the exhaust valve side, so it would still need valve reliefs cut.
Advancing the cam will hurt the top end revs(which I think extra revs are needed).
My thought since I profiled the cam has been that it appears to be retarded relative to similar cams. Similar cams seem to follow the timing of the stock cam a bit closer than this one. Plus, I noted that it took 2 degrees of advance to make the timing marks on the Hoca cam align where they should with the head at TDC. 2 degrees wouldn't get me far though. As mentioned earlier in the thread, if there were such a thing as a cam card for these, at least I'd know where I stand relative to intended timing.
We made our own relief cutters with old valves by either epoxy bonding very course sand paper the face and spinning them with a drill motor with the head installed ,or cutting notches in the face of an old valve and doing the above,,We'd try to find the next bigger valve to fab a cutter(1.94 valve,2.02 cutter),maybe there is a better way these days,but we still MUST maintain the proper 'crash' clearance in all 4T motors..2T's have their quirks,but not near as many when stuff starts bending at high revs!!
I used a circular flat stone to cut reliefs on my old SunL's BBK long ago. It's certainly not as precise or easy as using the head and guide to guide the cutter, but it did work.
PPS,What would you have with a thin base gasket with the stock setup??
I'd have a kit in need of a new piston... I guess kind the same thing I'd have if cutting reliefs in this one doesn't go well. I may check it out more.
I'm thinking I should aim for 0.050" P2V on the intake side and 0.080" on the exhaust side. I have talked to 190mech and frank50e about clearances in the past, because there just isn't much info... really any I've seen... out there for these small scooter engines. 0.050" was somewhat settled on as a reasonable street clearance minimum, and I don't recall any mention of wider clearance on the exhaust side. In the motorcycle world, 0.050" IN / 0.080" EX is a common recommendation. Another thought I've used is 2-3% of stroke length. That number came around from John/190 I believe, as a number for 2T squish setting at one point, but seemed like it could apply here. That would put it at 0.046" - 0.068". I hate not having solid numbers, so unless we come up with any, I will look for the wide ones to stay on the safe side. That's a lot of material removal from the piston though, to go from near nothing to 0.080".
I love these simple bolt-ons!
It didn't get squished nearly as bad as I expected. It was about 0.040" to 0.050". Most motorcycle info says to look for 0.035". I was hoping maybe it would be very tight, so then I could come up with a thin gasket and have a squish clearance near that spec and be closer to a reasonable P2V clearance.
At that point, my thought was that I may see what I could do with a few degrees of camshaft advance. How to do that though? Oh right, I ordered this adjustable cam gear since the BBK seller carried it as well.
The stock cam had a couple of markings, but I made new ones that aligned with the lines and holes used to ID proper TDC to make it a little easier to get it near it's original timing when the new gear goes on.
I pressed the old gear off and bent the gear. I've only messed with one other cam gear, and it did not take the amount of force to remove the gear that this one did. As long as the adjustable gear isn't junk, it shouldn't matter.
I centered the cam sprocket the best I could in it's grooves and so the top hole aligned, and made marks where the two side holes are so I'd be able to see them when the cam gear is apart.
I heated the section of the new gear that I needed to press on and aligned it the best I could. Then I pressed it on. When I started getting near where I thought it may need to sit, I kept installing the cam to see how the alignment was with the chain and guides. I probably should have just measured my stock cam or compared to that, but I didn't even think of it at the time. I ended up with the gear almost as far as it would go on and alignment looked good.
My plan was to see what a little advance would do for P2V clearance tomorrow. Obviously any reasonable amount isn't going to solve 0.002" (if that) on the exhaust valve side, so it would still need valve reliefs cut.
My thought since I profiled the cam has been that it appears to be retarded relative to similar cams. Similar cams seem to follow the timing of the stock cam a bit closer than this one. Plus, I noted that it took 2 degrees of advance to make the timing marks on the Hoca cam align where they should with the head at TDC. 2 degrees wouldn't get me far though. As mentioned earlier in the thread, if there were such a thing as a cam card for these, at least I'd know where I stand relative to intended timing.
I used a circular flat stone to cut reliefs on my old SunL's BBK long ago. It's certainly not as precise or easy as using the head and guide to guide the cutter, but it did work.
I'd have a kit in need of a new piston... I guess kind the same thing I'd have if cutting reliefs in this one doesn't go well. I may check it out more.
I'm thinking I should aim for 0.050" P2V on the intake side and 0.080" on the exhaust side. I have talked to 190mech and frank50e about clearances in the past, because there just isn't much info... really any I've seen... out there for these small scooter engines. 0.050" was somewhat settled on as a reasonable street clearance minimum, and I don't recall any mention of wider clearance on the exhaust side. In the motorcycle world, 0.050" IN / 0.080" EX is a common recommendation. Another thought I've used is 2-3% of stroke length. That number came around from John/190 I believe, as a number for 2T squish setting at one point, but seemed like it could apply here. That would put it at 0.046" - 0.068". I hate not having solid numbers, so unless we come up with any, I will look for the wide ones to stay on the safe side. That's a lot of material removal from the piston though, to go from near nothing to 0.080".
I love these simple bolt-ons!
