1975 350 Mark 3 camshaft identification

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IanA
Posts: 39
Joined: Fri Sep 23, 2016 4:43 am

1975 350 Mark 3 camshaft identification

Postby IanA » Tue Jul 07, 2020 5:53 pm

My 350 Mark 3 has been playing hard to start since i bought it. tried 4 different carbs, various timing settings and each time,i can occasionally get it to fire and run but then it wont restart.
On checking the valve clearances, and no 2 points of reference seem to quote the same clearance, they seem tight. They measure 1.5 thou inlet and 3.5 thou exhaust. Now the haynes quotes based on which camshaft it is, but of course after 45 years there is no factory colour code paint.
searching this illustrious forum showed quite a lot of information on 250 camshafts and base circle/lobe measurements, so i am hoping someone can shed some light on which i have.
My belief is it should be either a white camshaft or a green and white.
the measurements are thus:
Base circle 19.98mm
inlet lobe 29.42mm
exhaust lobe 28.02mm

there doesnt appear to be any appreciable wear to any part of the camshaft.
Any clues gratefully received on both camshaft ID and hence best valve clearances to suit.

Duccout
Posts: 1285
Joined: Wed Feb 05, 2020 1:20 pm
Location: Essex UK

Re: 1975 350 Mark 3 camshaft identification

Postby Duccout » Tue Jul 07, 2020 6:05 pm

I fear that the only way to be sure is to measure the timing with a degree disc, at least that will given you opening and closing figures, even if they are a bit out due to tappet clearances.

For comparison, I have a crazy Mototrans cam here that measures 22.9 on the base circle, 31.24 for the exhaust lobe and 32 for the inlet.

IanA
Posts: 39
Joined: Fri Sep 23, 2016 4:43 am

Re: 1975 350 Mark 3 camshaft identification

Postby IanA » Wed Jul 08, 2020 5:46 pm

I am the adage, a little knowledge is a dangerous thing!
Having watched a few youtube video on camshaft measuring, it is obvious i have mis-measured the base circle, it should be 19.5mm, which then gives 9.9mm of inlet lift and 8.5mm of exhaust lift, which funnily enough matches exactly a green and white camshaft, according to this post on this forum viewtopic.php?t=195

so happy days, i have a green and white camshaft and the clearances have been set for a white, and therefore the clearances are massively too tight, and most likely the cause of the rare starting, and no starting once warm.

Now to buy shims and put it back together

ranton_rambler
Posts: 439
Joined: Sun Jun 04, 2017 11:33 am
Location: Stafford UK

Re: 1975 350 Mark 3 camshaft identification

Postby ranton_rambler » Wed Jul 08, 2020 6:30 pm

Have you eliminated ignition problems? My 175 would start but give up as soon as I tried to ride it. Turned out to be a bad condenser.
Ian

ducwiz
Posts: 604
Joined: Tue May 22, 2012 12:52 pm
Location: near Frankfurt, Germany

Re: 1975 350 Mark 3 camshaft identification

Postby ducwiz » Thu Jul 09, 2020 9:10 am

Image
This is a foto taken from Andy Nienhagen's website www. desmo.net.
It doesn't give all necessary dimension of the cams, but might be helpful, anyhow. Unfortunately, the white camshaft, which is very similar to the red-black version, is missing.

Hans

IanA
Posts: 39
Joined: Fri Sep 23, 2016 4:43 am

Re: 1975 350 Mark 3 camshaft identification

Postby IanA » Thu Jul 09, 2020 12:44 pm

Thanks Hans very useful photo


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