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Cylinder Head to Camshaft Housing oil port  Rating:  Rating
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 Posted: 03-05-2014 04:29 am
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bora450
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In 2011 there was a CAM OIL PORT thread with discussion about the recess size to be cut into the camshaft housing to accept an o-ring.

John Finch listed a groove be cut that is 1.20 - 1.30 deep (.047 - .051). The diameter of the roll pin that sticks out of the cylinder head is .317. Standard 0-ring size -012 has a diameter of .070 and an I.D. of .364 which is a pretty sloppy fit. The next smaller o-ring is .301, rather tight.

I have searched the forum for any info about the o-ring without success. Does anyone have an o-ring part number or size available?

Thanks, Claus

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 Posted: 03-05-2014 10:16 pm
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Jim Ketcham
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I can't confirm the dimensions of the groove, but assuming the dimensions you have in your post are correct a metric o-ring of 8.0mm ID (.315") should fit and is available in a variety of cross sections.

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 Posted: 03-06-2014 03:53 am
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pbahr
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Is there not a Service Bulletin to cover this issue?

Pete

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 Posted: 03-06-2014 04:07 pm
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Jim Ketcham
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Yes. Service bulletin JN76-2 issued 3/10/76 discusses this but only refers to the tool for making the recess and the o-ring part number. It does specify dimensions or o-ring size.

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 Posted: 03-06-2014 05:15 pm
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bora450
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I found a metric o-ring at McMaster Carr that is 1.6mm diameter x 8.1mm I.D., #9263K622, 100 for $6.32 but I don't know if the thickness is correct.

Before I purchase the McMaster Carr o-ring, Jim, can you provide the o-ring part number listed in the service bulletin? I searched the internet for the service bulletin without success.

Thanks, Claus

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 Posted: 03-07-2014 02:50 pm
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Jim Ketcham
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Claus,

The service bulletin specifies o-ring No. A907E620Z for the cam housing.  This part number shows up in many Lotus parts suppliers lists but no one gives the generic size.  It does come in the gasket overhaul kits supplied by Delta. 

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 Posted: 03-07-2014 02:51 pm
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Jim Ketcham
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CORRECTION.  The part number for the O-ring should be: A907E6202Z.

Sorry about that.

Jim

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 Posted: 03-07-2014 03:32 pm
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Jim Ketcham
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Claus,

I found some o-rings marked for the cam housing from one of my 907 gasket kits.  Trying to match it up it by eye the o-ring appears to be a dash no. 11 buna-n.  I am not sure that the o-rings in the overhaul kit are those specified by Lotus which I assume would have been 8.0 mm metric?

Thinking about this, who cares if it fits sloppy over the roll pin.  The seal between the cam housing and the head is whats important.  It appears to me that the cross section diameter is more important to give the proper interference fit between those surfaces.  Just my opinion.

Jim

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 Posted: 03-07-2014 07:54 pm
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pbahr
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Claus,

I sent you the Service Bulletin via email.

Pete

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 Posted: 03-08-2014 07:02 pm
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bora450
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John Fitch provided this in the aforementioned post.

O-Ring Counterbore Details:
.......... SPEC METRIC / Calc'd Inch Decimal / approx inch fraction
Dia. 12.30 -12.44 mm / 0.48425" - 0.48976" / ~31/64" (.484375")
Depth 1.20 - 1.30 mm / 0.04724" - 0.51181" / ~3/64" (.046875")

My groove is a little smaller at .475 diameter x .044 deep. So I calculated the volume of a hollow cylinder (the groove less the roll pin) at .0043 cubic inch and the volume of a torus (the McMaster Carr o-ring) at .0037 so the o-ring does just barely fit into the groove when compressed.

The sloppy fit -012 o-ring is too large for the groove at .0052 cubic inch and the -011 o-ring which has to be stretched to fit over the roll pin is good at .0045 cubic inch but has to be stretched .016 diameter which is quite long at the circumference. I'll go with the metric one.

I'll order the o-rings today in Viton since Buna-N is good to 250 degrees F and Viton is good to 400 degrees F. They come in a pack of 25 (not 100 as previously written) and I only have two engines so there are plenty left. If anyone wants a couple, send a stamped, self-addressed envelope to:

Claus Groth
1795 Sweet Briar Place
Thousand Oaks, CA 91362

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