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Old 01-01-2013, 09:57 PM   #1
SamH OP
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Location: Tasmania, Australia
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How to identify airhead cams?

I've got two cams that came with my R90 project and I've no idea which one to use when I put it back together. The lobes measure up differently between the two but I haven't been able to find much in the way of information on airhead cams.

Here's a pic of the two.

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Old 01-02-2013, 06:06 PM   #2
supershaft
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It looks like it might be a 336 on the our left. I don't know what the marking are on those earlier cams. It could be other cams as well. You might have to time it to find out. If it's a 336 it could be a very early one timed straight up. That I would want to know for sure.
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Old 01-02-2013, 06:37 PM   #3
Kai Ju
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Except the left cam looks to be in rough shape, especially the oil pump drive area.
I would try and clean it up before I'd even consider using it.

Kai Ju screwed with this post 01-02-2013 at 08:24 PM
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Old 01-02-2013, 09:27 PM   #4
supershaft
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Except the left cam looks to be in rough shape, especially the oil pump drive area.
I would try and clean it up before I'd even consider using it.

It might just be stains. I hate stains but the FAA says that stained metal doesn't warrant rejection. It looks ruff but it might be usable.
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Old 01-02-2013, 10:24 PM   #5
SamH OP
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Yes, the cam on the left certainly looks a bit rough but it's really not that bad, the picture looks much worse than reality. It's mostly staining.
How do I go about figuring out the numbers on these two, do I have to have the top end together?
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Old 01-03-2013, 03:08 AM   #6
SamH OP
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Ok, I measured up the cams tonight as best I could. Put them both in the lathe and setup the dial gauge. I could only measure lift.

The cam marked 921 measured 6.75mm lift on all four lobes, x1.39 = 9.3825mm or 0.3693"

The cam marked 630 measured 7.64 lift or near enough on all the lobes, x1.39 = 10.6196mm or 0.4180"

Is lift alone enough to identify these two? Is there a list of specs somewhere?
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Old 01-03-2013, 11:27 AM   #7
supershaft
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You could probably get a good idea from lift alone but there are a lot of cams out there now and a lot of them have just about the same lift.

There are usable specs out there for a 336, 308, Andrews, Megacycle, Crane? Chances are it's a 336 but . . . . Either way you will need to time it in order to see how it is timed. Chances are if it's a 336 it is timed 3* advanced but it might be timed straight up since it has the old style oil pump drive. I suggest reading a few books on timing cams. Other inmates know how to post the specs. There is two more recent cam threads that have most of the specs I referred to. Some inmates don't like cam discussions. It gives them a headache. It is a bit more complicated than removing grips!
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Old 01-03-2013, 04:45 PM   #8
disston
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Yeah. But removing grips is were the real money is.
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Pay your debt, piratejohn.http://www.advrider.com/forums/showthread.php?t=949341
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Old 01-03-2013, 05:38 PM   #9
supershaft
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It's been cracking me up.
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Old 01-03-2013, 06:47 PM   #10
motu
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I removed and replaced my left hand grip yesterday just to see if I could do it - thank God for ADVRider!
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Old 01-03-2013, 09:57 PM   #11
SamH OP
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I know, it's a good thing this bike's in bits. I only have to worry about installing a new set of grips. Phew.

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Old 01-04-2013, 04:47 PM   #12
mattcfish
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Quote:
Originally Posted by SamH View Post
Ok, I measured up the cams tonight as best I could. Put them both in the lathe and setup the dial gauge. I could only measure lift.

The cam marked 921 measured 6.75mm lift on all four lobes, x1.39 = 9.3825mm or 0.3693"

The cam marked 630 measured 7.64 lift or near enough on all the lobes, x1.39 = 10.6196mm or 0.4180"

Is lift alone enough to identify these two? Is there a list of specs somewhere?
BMW specs.
308 has a lift of 9.4mm
336 has a lift of 10.68mm
284 has a lift of 8.62mm

Lucky you. #630 has the lift of a 336. An early one with a key drive on the OP is a rare thing......#921 is a 308.
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Old 01-04-2013, 08:43 PM   #13
SamH OP
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Ahh, finally some numbers! Thanks heaps for that. I'll just have to take it at face value and accept that it's ok to use. I'll see if I can compare the two cranks and figure out if they're timed the same.

I've got the lightened flywheel, 9.5:1 pistons and dual plugged heads so hopefully all those bits will combine to make a nice poweful engine.
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Old 01-05-2013, 01:34 PM   #14
mattcfish
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Quote:
Originally Posted by SamH View Post
Ahh, finally some numbers! Thanks heaps for that. I'll just have to take it at face value and accept that it's ok to use. I'll see if I can compare the two cranks and figure out if they're timed the same.

I've got the lightened flywheel, 9.5:1 pistons and dual plugged heads so hopefully all those bits will combine to make a nice poweful engine.
Actually the timing difference is where the key slot is positioned for the cam sprocket. It's just a hair difference. The slot is 3 degrees retarded which advances the valve timing by 6 degrees (cam spins half as fast as crank). There are several different opinions as to why this was done. Emissions regulations, to increase mid-range, or to improve idle. Your slotted oil pump, points style cam probably has strait 0 degree valve timing. Not sure, but I think the advanced cams came out with the bean cans.
I'm using the later bean can 336 on my /6. I've got light 9.5:1 1000cc pistons in Nikasil cylinders, titanium valve retainers, dual plugs, crank ignition, 1983 tranny with ultra light clutch/non-existent flywheel , 32/11 rear end , 2 into 1, and 38mm Dellortos (with spot on jetting). Gotta say I love this combo with the 336.
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Old 01-05-2013, 04:57 PM   #15
supershaft
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Quote:
Originally Posted by mattcfish View Post
Actually the timing difference is where the key slot is positioned for the cam sprocket. It's just a hair difference. The slot is 3 degrees retarded which advances the valve timing by 6 degrees (cam spins half as fast as crank). There are several different opinions as to why this was done. Emissions regulations, to increase mid-range, or to improve idle. Your slotted oil pump, points style cam probably has strait 0 degree valve timing. Not sure, but I think the advanced cams came out with the bean cans.
I'm using the later bean can 336 on my /6. I've got light 9.5:1 1000cc pistons in Nikasil cylinders, titanium valve retainers, dual plugs, crank ignition, 1983 tranny with ultra light clutch/non-existent flywheel , 32/11 rear end , 2 into 1, and 38mm Dellortos (with spot on jetting). Gotta say I love this combo with the 336.
Cam specs are all at the crank. A cam that is advanced three degrees is advanced three degrees at the crank (and valves). Six degrees at the crank would adversely effect the exhaust timing too much by most tuners' opinions. Most tuners consider five degrees the absolute max to advance or retard a single cam. Most don't go past three degrees (at the crank). That's 1.5 degrees at the cam. Advanced or retarded at the cam? That all depends if it is gear or chain drive but most all tuners call what ever it is doing at the crank how they are modifying the setup at the cam.

Advancing the sport cam had nothing to do with emissions since the cam was never in a regulated bike. Advancing the 308 had to do with emissions but . . . . I don't know anyone that has changed a cam timing for idle. The timing was changed to lower peak torque around 500 rpm. Most single cams can be retarded and advanced three degrees for a total of six degrees to play with in order to move peak torque around about 1000 rpm.

As I understand it, they advanced the 336's timing before they changed the oil pump drive so this one could be either straight up or advanced.

I have a 336 in my '92 R100 which includes the later, lighter clutch and single row timing chain. 9.5:1 pistons. .025 off the heads. Titanium valve spring retainers. Custom made 4130 pushrods. 44mm intakes with modified valve head/seat ID ratio. Heavily re-shaped ports. Dual plugged with stock bean can and re-mapped ignition curve. Completely re-jetted 38mm Dellorto carbs. Heavily modified airbox. Staintune Sport mufflers. 33/11 FD. The thing makes WAY more power EVERYWHERE in the rev range including at least 1000rpm on top that it never had to start with! I love it!

I ran mine for over ten years without raising my stock 8.5:1 CR or much port work at all with great improvements from around 2500 rpm on up but now I wish I had raised the CR and ported my bike like I did just recently a long time ago. The thing is now running a LOT better than it was and it was already running a lot better than stock!

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