Planet Minis

qa50 · 12-05-2006, 10:58 PM

Hey guys,

Just wondering how i can tell the differnce both externally and internally between a 50cc head and a 70cc head? I know the 70's have bigger valves but is there a way to tell from the outside?

Cheers

QA50

fastbmw · 12-05-2006, 11:31 PM

I believe externally they are identical. I've had both the 50cc head and the 70cc head and I couldn't tell the difference between them. The only way you can tell internally is the bigger valves (which you knew) and the combustion chamber is a lot larger on the 70 head.

Here's a xr70 style head, notice the deep dish of the combustion chamber

qa50 · 12-06-2006, 02:40 AM

Ok cool, what about the difference between a 6V head and a 12V head?

arlindsay1992 · 12-06-2006, 05:41 AM

6v and 12V can be told by taking off the round cam cover. Just look at the cam and see if it is a ball bearing cam or a journal cam. And to tell between 50cc and 70cc heads, look at the size of the carburetor port. Will be bigger on the 70.

davez · 12-06-2006, 08:10 AM

So Quoke , will the same cam chain run on 6v or 12v head?

lowbike1 · 12-06-2006, 08:35 AM

Quote:

Originally Posted by davez

So Quoke , will the same cam chain run on 6v or 12v head?

yep

arlindsay1992 · 12-06-2006, 04:21 PM

Yeah. And the same sprocket too. 28 teeth if I remember correctly. I might be wrong. Well same number of teeth on the sprocket. But the older 6v heads had three bolts that were offset so that the sprocket could only go on one way. The newer 12v heads have only two bolts and you have to make sure the sprocket isn't on backwards.

12-05-2006, 10:58 PM	#1 (permalink)
qa50 1st Gear Member Join Date: Dec 2006 Location: Australia Posts: 104	6V Cylinder Head ID Hey guys, Just wondering how i can tell the differnce both externally and internally between a 50cc head and a 70cc head? I know the 70's have bigger valves but is there a way to tell from the outside? Cheers QA50

12-05-2006, 11:31 PM	#2 (permalink)
fastbmw 2nd Gear Member Join Date: Sep 2005 Posts: 643	I believe externally they are identical. I've had both the 50cc head and the 70cc head and I couldn't tell the difference between them. The only way you can tell internally is the bigger valves (which you knew) and the combustion chamber is a lot larger on the 70 head. Here's a xr70 style head, notice the deep dish of the combustion chamber Last edited by fastbmw; 12-05-2006 at 11:42 PM.

12-06-2006, 02:40 AM	#3 (permalink)
qa50 1st Gear Member Join Date: Dec 2006 Location: Australia Posts: 104	Ok cool, what about the difference between a 6V head and a 12V head?

12-06-2006, 05:41 AM	#4 (permalink)
arlindsay1992 "High Speed Record Guy" Join Date: Mar 2006 Location: Northern Virginia Posts: 4,369	6v and 12V can be told by taking off the round cam cover. Just look at the cam and see if it is a ball bearing cam or a journal cam. And to tell between 50cc and 70cc heads, look at the size of the carburetor port. Will be bigger on the 70.

12-06-2006, 08:10 AM	#5 (permalink)
davez 2nd Gear Member Join Date: Dec 2005 Posts: 769	So Quoke , will the same cam chain run on 6v or 12v head?

12-06-2006, 04:21 PM	#7 (permalink)
arlindsay1992 "High Speed Record Guy" Join Date: Mar 2006 Location: Northern Virginia Posts: 4,369	Yeah. And the same sprocket too. 28 teeth if I remember correctly. I might be wrong. Well same number of teeth on the sprocket. But the older 6v heads had three bolts that were offset so that the sprocket could only go on one way. The newer 12v heads have only two bolts and you have to make sure the sprocket isn't on backwards.

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