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Post by magoconnor on Jan 19, 2018 14:43:08 GMT -5
Hello.
I'm looking for a big valve head for my 72cc 139qmb, but I'm having hard time finding one (especially in europe).
I will appreciate all the help I can get.
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Post by 90GTVert on Jan 19, 2018 17:07:07 GMT -5
I know of a few for larger bores. Not too sure what you can get over there for 47mm bore. Naraku, Taida, NCY, HOCA or SSP-G are a few Taiwan brands that have big valve heads for larger bores (50mm+). ScrappyDogScooters here in the US sells a head that they recommend for 47mm and up bores. Not sure if they'll ship to you... www.scrappydogscooters.com/139QMB_50cc_Performance.html |
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Post by 90GTVert on Jan 19, 2018 17:11:14 GMT -5
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Post by lilpinny on Jan 19, 2018 17:44:28 GMT -5
The trick to buying stuff from the US is get a buddy to ship it to you. Buy it and have it shipped to a friend in the US. Then have that friend take it out of the packaging (so it takes up less space) and pack it in a US postal service international flat rate box. Ship that plus whatever else you can fit in (it’s one price for whatever you can fit) and ship it.
Source: me. Former US expat that lived in Melbourne, Australia
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Post by magoconnor on Jan 19, 2018 21:57:31 GMT -5
Hello.
Thanks for the help, feel free to post more links ( if you find any)
I'm thinking about maybe going with the first aliexpress link.
Do you think it will lower the combustion to much ?
i will be runing it with a performance cam and a 21mm carb.
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Post by 90GTVert on Jan 20, 2018 6:21:39 GMT -5
It's definitely gonna drop compression with the larger chamber. Can't say for sure if the compression or the big valves will do more for you. With some effort, you may be able to bump up the compression with that head. You could check squish and piston to valve clearances and have some milling done or just use a sealant instead of a base gasket if clearances will allow.
I would suggest looking over the ports before installing the cheap heads. Not a bad idea with any head really, but the cheap ones have some very poor casting sometimes. You can even see it in the ad on the second head.
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Post by magoconnor on Jan 20, 2018 11:33:33 GMT -5
Hello again.
the combustion chamber on most "big valve" heads are 50mm.
I hope it will turn out for the better.
do you think I will have any clearance issuses?
my scooter is kymco agillity 139qmb 72cc
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Post by 90GTVert on Jan 20, 2018 13:29:26 GMT -5
the combustion chamber on most "big valve" heads are 50mm. The reason I linked to the ones that I did are because they say 47mm. I can't tell you what they truly are. I wouldn't want to use a 50mm head on a 47mm bore, because the mushroom shape it would create seems like a terrible idea to me. do you think I will have any clearance issuses? If it's OK now, it is likely fine with a new head unless the big valves don't match up with the reliefs in the piston and it makes for tighter clearances. I was mostly referring to clearance issues if you tried something like using sealant instead of a base gasket or had the head or cylinder milled. |
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Post by magoconnor on Jan 20, 2018 19:28:29 GMT -5
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Post by 90GTVert on Jan 20, 2018 19:44:12 GMT -5
The look like standard size valves in the pic. Not sure you can fit the big valves in the stock bore too well.
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Post by magoconnor on Jan 21, 2018 13:44:04 GMT -5
oh damn..
You never know with these chinese dealers.
I think the "big valve" head is the only upgrade I really need or at least the only mod I can do, without upsizing the bore diameter. What do you think? Any upgrades you can think of?
My Setup
139qmb
72cc cylinder
standard head
Performance cam ( not a9! but still a good one)
21mm carb
unifilter
Performance exhaust
Naraku 32000 v coil
Bigger intake manifold polished
Port matched intake/ exhaust
Advanced the timing ( with your free mod)
Performance variator and clutch
Medium tension spring
Removed all restrictions.
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Post by 90GTVert on Jan 21, 2018 14:10:42 GMT -5
A BVH sounds worth trying at this point. Once you get a bunch of bolt-on kind of mods, it gets to be about time and effort and refining what you have. That's when it gets tougher to get gains. Not sure that the polished intake is great. Not sure that it matters a ton. Generally wet intakes (where fuel is in the mix, as opposed to dry where it would be later injected) are left with some texture. You don't want a bunch of casting flaws, but you don't want to see yourself in the inside of the intake. If you really want to be sure you're getting the most from it, you can do things like being sure the tune is really dialed in (carb and CVT). Takes time and patience. Sometimes gains are large, but if it's close now you may not get a lot out of it. You can put a bunch of effort into the stuff I mentioned before. You can cc the combustion chamber and piston and do the math and find compression ratio to see where it's at and then decide what can be done or if you'd want to change it at all. That would be interesting to know with the change from stock head to BVH. You could see a large drop with a big chamber. You can try to tighten up the squish band if needed, which could raise compression and should make the engine less prone to detonation. You can play with timing more like using an adjustable CDI possibly in conjunction with the current mod. There's a lot that can be done, but again the time and effort goes way up once you pass the bolt-on phase. If you're really interested in this stuff, consider reading books like A. G. Bell's " Four-Stroke Performance Tuning" or " How To Build Horsepower" by David Vizard. There are a lot of good books out there on engines, if you can look beyond the fact that most of them dwell on V8s. |
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Post by magoconnor on Jan 21, 2018 20:20:36 GMT -5
Ok sounds good. But thanks alot, you have been very helpful.
Just out of curiosity, have you or somebody you may know seen any gains with a BVH ?
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Post by 90GTVert on Jan 21, 2018 21:54:21 GMT -5
I had a BVH on a 50mm bore that ran well. There have certainly been forum members that had good results with different heads.
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