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Old 07-01-2012, 02:32 AM   #1
a_bakla OP
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Airhead camshafts

I ve searched old posts and read other documents and there are tons of different camshafts. I am rebuilding my G/S and want to put siebenrock big bore kit .For high torque at low rpm which cam is right choice ? hpn324 or siebenrock 336 or any other?
I need some advice

http://www.motoren-israel.com/index...._Camshaft.html
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Old 07-01-2012, 02:18 PM   #2
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I don't recommend their big bore kits past 94mm. The cylinder walls become too thin and distort too much IMO.

As far as I know Siebenrock does not publish their cam specs so you can compare them?

Displacement is king but I don't see turning your super short stroke airhead engine with a 1.33:1 bore to stroke ratio into a tractor engine by shortening the bore/stroke ratio even more via the bore to 1.37:1 I believe. I think those are 97mm bores? Most tuners reduce the bore/stroke ratio for low RPM power but that involves stroking the engine. There's room for a 10mm longer stroke at the piston but I don't know about the crank case? Or the crank itself for that matter? 94x80.6mm bore/stoke gets you down to 1.17:1 over square for 1120cc's. It's still a short stroke engine but at least your going in the right direction.

I still think it is funny that beemerphiles call R65's short stroke engines all the time but don't refer to our R100's as the same. The both have the exact same bore to stroke ratio. The term "stroke" is relative!

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Old 07-01-2012, 02:43 PM   #3
a_bakla OP
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Oooopppsss !!! I wrote it incorrectly ! İt should be 1000cc kit, not big bore kit.
İs it worth changing the stock 308 for 1000cc kit ?
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Old 07-01-2012, 02:54 PM   #4
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stock 1000 cc BMW engines use the same cam as the 750,800,900 cc engines.
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Old 07-01-2012, 05:11 PM   #5
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I'm wondering why youre even considering swapping cams. What size engine are you running now? Are you looking for lower RPM power or do you want to move the torque peak higher? How do you use your bike?

I don't want to sound like an ass but those are the major questions that I'd want to answer before jumping into an expensive engine rebuild and trust me... A lot of guys have spent big bucks building engine that they didnt like once they started riding thier rebuilt bike or Hot Rod.

I have a brand new 336 cam thats been sitting on the garage shelf for amost two years. Maybe someday but right now I have more than enough headaches!
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Old 07-01-2012, 05:19 PM   #6
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Quote:
Originally Posted by supershaft View Post
I don't recommend their big bore kits past 94mm. The cylinder walls become too thin and distort too much IMO.

As far as I know Siebenrock does not publish their cam specs so you can compare them?

Displacement is king but I don't see turning your super short stroke airhead engine with a 1.33:1 bore to stroke ratio into a tractor engine by shortening the bore/stroke ratio even more via the bore to 1.37:1 I believe. I think those are 97mm bores? Most tuners reduce the bore/stroke ratio for low RPM power but that involves stroking the engine. There's room for a 10mm longer stroke at the piston but I don't know about the crank case? Or the crank itself for that matter? 94x80.6mm bore/stoke gets you down to 1.17:1 over square for 1120cc's. It's still a short stroke engine but at least your going in the right direction.

I still think it is funny that beemerphiles call R65's short stroke engines all the time but don't refer to our R100's as the same. The both have the exact same bore to stroke ratio. The term "stroke" is relative!
Out of interest how would you go about stroking it?
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Old 07-01-2012, 05:38 PM   #7
supershaft
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Quote:
Originally Posted by Voltaire View Post
Out of interest how would you go about stroking it?
I would start by never doing it. Go ride a R12C and feel what they are looking for in strong low RPM power. That is not what I am looking for.
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Old 07-01-2012, 07:14 PM   #8
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Use the Siebenrock sport cam not the BMW one.
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Old 07-01-2012, 10:10 PM   #9
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OH BOY!
A new camshaft thread, yeehaw!
Cancel my reservation.
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Old 07-02-2012, 07:51 AM   #10
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My Seibenrock 1070 kit is working fine after 3 years and 10000 or so miles. The kit comes with the Seibenrock assymmetrical cam. Works well at low revs ans has a nice kick from around 5000 rpm. Up to 50 mpg and 72 RWHP.
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Old 07-02-2012, 09:52 AM   #11
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I have 70,000 miles on a BMW sport cam. Works well at low rpm and has a great mid and upper rpm power boost. I had to take it apart recently with 101,000 total miles for toasted exhaust guides. The rest of the top end could have gone a while longer but the stock BMW nikisil crosshatch was close to all gone so I got new cylinders. The top of one top ring groove was worn like they do so I got new pistons too. The BMW sport cam and lifters were perfect after 70k miles. They went right back in!

In my experience with lined big bore kits, it takes about 10k miles for the cylinder wall to start looking like a corrugated pipe. The corrugations would be in perfect step with the cylinder fins. You could run a Sunnen hone down the bore and SEE it.

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Old 07-03-2012, 02:13 PM   #12
mattcfish
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I've got the Seibenrock 1000cc kit and a 336 cam on my 1975 R90/6. Stock R90 Heads, but dual plugged, and 38mm Dellortos. Love the combination. With the right jetting (thanks SS) I've got loads more pull at mid range and it's down right scary at high RPM. Very fun and responsive. Can't speak for the other aftermarket cams, the 308 will give you a better idle and MPG, but the 336 really gives it the extra grunt I was looking for. If you do put a new cam in, invest in the cast iron front bearing carrier with the bronze bushing. The aluminum ones ware very quickly on the sides. Have you checked Motoren Israel's cams? Not sure if they are the same as Siebenrock or not.
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Old 07-03-2012, 03:19 PM   #13
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The later aluminum front bearings work fine with 336's. I think there was only a problem with early ones?

I wanted to add that there is all kinds of stuff you supposedly should or 'have' to do to run a BMW 336. A good friend of mine insists as others do that you HAVE to run steel pushrods with a BMW 336. I used aluminum ones with mine for 70,000 miles. They show no signs of flexing any more than they always do running a 308. Which is a lot by the way.

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Old 07-03-2012, 10:01 PM   #14
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I was just thinking mattcfish that my bike idles just as well with a sport cam as it does with a 308. Well close enough that NO ONE has ever been able to tell that it has a 336 in it from the idle. Including Duane Ausherman (sp?). He told a small crowd around my bike at a rally that there was no way my bike had 336 in it because it idled too well. My girlfriend and I didn't make a sound except for maybe letting out a giggle. She helped me put it in!

At any rate, I am getting more and more convinced that a lot of the '336's don't idle" BS is not caused by the cam itself but the cam in combination with leaking valves. That and the carb setup IS a bit more picky with a 336 in there. After saying all that and despite the fact that Duane said that is was idling like a perfectly set up 308, my bike will occasionally and totally randomly hiccup while idling since the 336 was installed. Very rarely the engine quits running for it. But other than that . . . . It's only going to idle better since I raised the CR up from 8.5:1 to right around 10:1 but my break in has had a huge interruption in it for my shock stud snapping off. I am getting better but now they might have to operate on my hip if some steroid shots don't help it.

supershaft screwed with this post 07-03-2012 at 10:11 PM
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Old 07-03-2012, 10:12 PM   #15
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I agree with S/S, if it doesn't idle the same with a 336 as it does with a 308 there is something wrong.
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