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300° BMW Motorsport cam

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Hi guys,

I've just bought a 300° BMW Motorsport cam on E-bay.

How can I be sure of this?

On the cam I see:

5(raised) R118 0083.2

M(double M) 439

The first bearing is 45mm and the middle is 44mm.

This cam fits in a 121TI head R12102500809 with the same size for the bearings.

Is this a matched pair?

What inlet valves should I put in this head : 44mm or 46mm?

Do I have to change the valve seats for unleaded gas?

Thanks,

Michel - Belgium

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Guest Anonymous

I am sure one of the parts guys here can confirm the correct BMW part number, I had one of these many years ago in my tii/A4 car, I had an E12 head that had 46mm intakes and 39 mm exhausts - Standard for ALPINA - I dont know that the head so much as matters however I do know that my e12 head center bearing had to be "ine bored" larger to allow the large lobes of the cam to fit through, otherwise there is no way that I am aware to fit the cam into a stock head 121 or e12 (or e21).

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I've just bought a 300° BMW Motorsport cam on E-bay.

How can I be sure of this?

You need to measure the cam to verify what it is.

BMW had the Sport 300 cam mark with a "3" on the edge of the chain sprocket flange, just next to the TDC notch mark. There are so many possible versions of regrinds that there is no way to tell what a used cam is now without measuring things like base circle, lift, journal size, or duration.

The BMW Sport 300 cam requires the cylinder head get line-bored to fit the first two cam journals, each of which are enlarged 2 mm.

Stock cam journal 43 / 42 / 35 mm

Sport 300 journal 45 / 43 / 35 mm

The larger BMW Sport 324 & the big Schrick cams also share this large journal size. I have a Schrick 304 made for big journals, where the regular production 304 is now made with stock journals and requires the "notch" be made on your cyl head to clear lobes on installation.

BMW Sport 300 specs:

Inlet open 45 deg BTDC

Inlet close 75 deg ABDC

Exh. open 75 deg BBDC

Exh. close 45 deg ATDC

Inlet lash 0.008" cold

Exh. lash 0.010" cold

Note the difference from the stock cam's clearance settings.

See the pic below, those are two NOS 300 cams in the cardboard tubes.

The number "3" stamp is not real clear on the sample shown, but that's its location.

On the cam I see:

5(raised) R118 0083.2

M(double M) 439

Those are casting numbers, they don't really identify what cam profile was ground from that blank.

This cam fits in a 121TI head R12102500809 with the same size for the bearings. Is this a matched pair?

The big journal cam will fit in any M10 cam that has had the first two cam bearing bores enlarged, either by BMW or a machine shop the customer finds. That R12102500809 is just another casting number (for the stock 121T head) and gives no indication it is ready to accept the big journal cams. If yours does have the enlarged journals, then you are OK.

Which head you choose to start with may depend on what pistons you want to use, but I'd rather use a better flowing head like the E12 or 1.8i that has been line-bored.

What inlet valves should I put in this head : 44mm or 46mm?

Do I have to change the valve seats for unleaded gas?

I would go with the larger valve size if you can. The seats are hardened for unleaded, as far as I know. This concern seems to come up more often from ECE or UK owners, here in the USA no one ever did "conversions" to run unleaded, and the valve seats have not suffered.

Enjoy your 300 cam! Use high compression pistons and you will have a great result!

post-687-13667585166066_thumb.jpg

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Thanks John,

Yes, I see the "3" on the edge of the chain sprocket flange, just next to the TDC notch mark! So it is a 300° BMW, whow!

It is a bit odd to identify a cam with only one digit. I wonder why they didn't put the part # 11 31 0 631 009 on it as on the orange sticker on your picture.

I understand you'd prefer to go with an E12 head and have the journals line bored rather than using the 121TI I've bougth with the cam.

In that case I should use the tii "raised grand piano" pistons 9.5:1.

I thought that the 121TI (with a smaller combusion chamber) could give more compression with tii "121" pistons giving 10:1.

What did you do for your car and what is the result?

Cheers,

Michel

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Bring back some life to this topic. 

 

I just walked in to a head including camshaft. The numbers are the same as on Michel's, but on the edge of the chain sprocket flange there is an 4. I know a 2 is standard, 3 is an 300 deg, who knows what an 4 is? 

 

thnx!

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4 Would indicate that it is a factory 328 cam. That cam needs 11:1 comprssion or higher to be usefull. G

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To confirm what gracer is saying that cam would also be internally oiled and therefor have a small oiling hole on the backside of each cam lobe.

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I just walked in to a head including camshaft.

Ice it for a few minutes, then Ibuprofen works well for me...

 

heh...

 

I'm a huge fan of measuring the lobes, myself- if it's in a head, measure the

valve face closed and open.

 

If not, lobe dimension - skinny dimension gives you cam lift.

 

t

  • Haha 1

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4 means it's a 324 degree bmw Motorsport camshaft...

On my race car I have a rare bmw Motorsport 336 degree cam that has a number 5 stamped on it, the lobes are visually fatter and more overlap than the 324.

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90a04be9c4bc5d16a1e5c995f3247454.jpg

26d6deb90be87b7b0d70e858079aeb9c.jpg

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Verzonden vanaf mijn iPad met Tapatalk

Thnx for the respons and the info. So it looks like its an 324. I hope for an 300;)

Verzonden vanaf mijn iPad met Tapatalk

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I have a NOS cam that I believe is a motorsports 300 based on the tube that came. There is #3 stamped on the face where the sprocket mounts. I do want to double check the lobe lift but I could not find this info anywhere. 

The journal diameters are 45 43 35 and there is no internal oiling. Its also stamped 4 on the shaft somewhere, so I am confused. 

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Ireland HD rockers, and from your photos the back-side of the lobes have barely any wear pattern. How does the rest of the lobe faces look? If they're as blemish free as the back, it looks like it's been barely run, if at all. She sure is dirty, thou.

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 Two cams pulled from the 'bin' , reviving this old thread (it has a substantial amount of content on the topic).

 

Consider this post explorations in camshaft ID (or not). I will be measuring them later.

 

It seems the "3" might indicate a BMW Sport / 300° camshaft, but the journals are not oversized.

   Has anyone seen a 300° with normal-size journals?

BMW #3 camshaft

 

This cam has no markings near the TDC indicator, but has a "5" on the face.

   For those who have a #5 camshaft, is this how they are marked?

BMW #5 camshaft

 

Thanks, KB

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The only 300' cam that fit the normal bearings that I recall was from Alpina and is a very nice cam for street and light track.

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31 minutes ago, Son of Marty said:

The only 300' cam that fit the normal bearings that I recall was from Alpina and is a very nice cam for street and light track.

 

Thanks for that. We'll see how it measures-up next week. -KB

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