Does a cam tend to move longitudinally in operation?

[HCA]

Promotor posted a photo in another thread that made me have a quick look at my head that is near assembly.

New SAS head with new Kent (D144) cams.

I was alarmed to see that all the Kent cam lobes were not dead 'central' and wonder if this is normal and/or anything to worry about? The lobes cover the valve (and therefore pressure head of the follower) so I see no problem in operation (?). However, what is alarming is how close the rear of the lobes rotate past the cut out walls in the head - most clear well over 1mm, but one is a distance of .45mm from the cutout edge...

My questions - anything to worry about? does a camshaft want to move longitudinally rearwards in operation? should I maybe get out my trusty Dremel and remove some of the cutout wall?

[rgh0]

The cams are located by the thrust flange and slot in the head just behind the sprocket. Try moving the cam as far as this allows and see if any interference. If too close yes get out your dremel and carbide burr and open up the clearance a little.

Even with larger cutouts typically done on modified heads designed for high lift cams this can be an issue

cheers
Rohan

[HCA]

Thanks Rohan. I am glad I asked the question.

The thrust ring is a really good fit in its channel. I vut back a 0.1mm feeler that was a tight fit, so if cams generally stay in position, then it should not be an issue. But I think I will cut back some of the walls.

What would be a good clearance to have?

Is it unusual to have lobes slightly off centre?

[ill_will]

You've got me worried - I'm also building up an SAS head, with cams ground from Kent blanks. Good work catching the issue!

[HCA]

HaHa! Thanks goes to Promotor for posting his photo. I might not have picked it up otherwise!

Have you fitted the cams yet? I’d be interested to see if you have the same issue.

What is the spec of your SAS head and cams?

[promotor]

Promotor posted a photo in another thread that made me have a quick look at my head that is near assembly.

New SAS head with new Kent (D144) cams.

I was alarmed to see that all the Kent cam lobes were not dead 'central' and wonder if this is normal and/or anything to worry about? The lobes cover the valve (and therefore pressure head of the follower) so I see no problem in operation (?). However, what is alarming is how close the rear of the lobes rotate past the cut out walls in the head - most clear well over 1mm, but one is a distance of .45mm from the cutout edge...

My questions - anything to worry about? does a camshaft want to move longitudinally rearwards in operation? should I maybe get out my trusty Dremel and remove some of the cutout wall?

IMG_4775.jpeg

They aren't always dead central and I always check which side the cams I have sit in the best and have the best clearance on the largest number of cam lobes. Sometimes you'll get a situation where a cam simply won't fit / rotate without catching something, or won't rotate at all. The head then needs a bit of clearance work with a little grinding / fettling.
It's always worth checking a cam rotates without catching anything and with the cam at both ends of its endfloat (provided for by way of the large thrust ring). I've seen some engines running with 0.010" clearance between lobes and follower bores - it's worth not only checking the sides of the lobes but also the nose of the lobe to make sure it's not too close to follower bore top, which does happen with some high lift cams and follower bore lobe reliefs that aren't deep enough.

It might be worth swapping cams over from one side to the other to see "best fit".

[2cams70]

The cam end thrust location groove in the head is worth checking for wear whenever you take apart a head (although Rohan and I seem to disagree on this point). In practice as this groove wears the cam position will move slightly. This movement will be in very small amounts gradually micron by micron. If through natural wear the lobe with the least clearance eventually contacts the edge of the follower bore it's no big deal because it's a very gradual process and the two contact surface will just wear in together. It's not as though the two surfaces will suddenly smash together. I'm not saying there should be no clearance - all I'm saying is it's not worth getting too hung up about it because Lotus didn't seem to get too hung up about it either.

[rgh0]

The cam end thrust location groove in the head is worth checking for wear whenever you take apart a head (although Rohan and I seem to disagree on this point). In practice as this groove wears the cam position will move slightly. This movement will be in very small amounts gradually micron by micron. If through natural wear the lobe with the least clearance eventually contacts the edge of the follower bore it's no big deal because it's a very gradual process and the two contact surface will just wear in together. It's not as though the two surfaces will suddenly smash together. I'm not saying there should be no clearance - all I'm saying is it's not worth getting too hung up about it because Lotus didn't seem to get too hung up about it either.

The cam groove wear is very little and very slow and I dont disagree and it does occur. I recommend that every critical dimension in a head be measured and all crticial clearances checked including the cam thrust locating faces and lobe to head clearances on the sides and nose. The bigger problem in standard engines tends to be a sleeve rotating in the head ( typically when the engine overheats) and then hitting the cam lobe as this can occur quickly and lead to catastrophic damage

cheers
Rohan

[rgh0]

I would want around 0.5mm minimum clearance on the nose and sides of the cam lobe. Your minimum of 0.45mm is close to that and you could open it up a little if you wanted.

cheers
Rohan

[HCA]

Thanks everyone!

This morning I changed the cams over. Pretty well the same - a snug fit for the thrust ring, cams rotate freely, lots of room for the lobe nose maybe 2mm+ (being a Wilcox race head, it was maybe made for very high lift cams?) and where the lobe is close a cut-out side around a 1mm gap. It is just the one cut out with .45mm that does not look right, so I will widen it out to 1mm.

You have answered my question in saying wear on the thrust ring groove is minimal that gives me confidence!

[ill_will]

Have you fitted the cams yet? I’d be interested to see if you have the same issue.

What is the spec of your SAS head and cams?

They were fitted to get the valve clearances in the ballpark and nothing jammed, but I didn't explicitly confirm the nose clearances. I'm building the bottom end currently so have backed off the caps and cams so I can safely box it up. I'll dig it out and take a look.

Tim did me a full race spec head but his son, who is building a similar spec engine to me, programmed it with slightly smaller intake ports to suit dcoe40s, to try to maximise low end torque.

The cams are 0.437" 283/248 deg duration from Tony Ingram, from the numbers at least they seem pretty similar to the McCoy 450 that a few people like. (Iirc a few thou less lift and a couple of degrees less duration)

[khamai]

I was alarmed to see that all the Kent cam lobes were not dead 'central' and wonder if this is normal and/or anything to worry about?

IMG_4775.jpeg

An off center cam lobe is desired. It promotes the cam bucket to rotate and wear evenly.

Kiyoshi

[HCA]

Kiyoshi - thanks for this! Yet again, I learn something new!

Now, it makes sense. Looking closer at it just now, I can see how the lobes are perfectly positioned to rotate the followers.

I guess now that the bad boys are SAS who could/should have machined the cut outs a milimetre more to the rear..

[promotor]

Kiyoshi - thanks for this! Yet again, I learn something new!

Now, it makes sense. Looking closer at it just now, I can see how the lobes are perfectly positioned to rotate the followers.

I guess now that the bad boys are SAS who could/should have machined the cut outs a milimetre more to the rear..

That and a combination of the cam blanks ie where the lobes are actually positioned. This all boils down to Lotus' machining / manufacture not being tightly quality controlled in some aspects - there don't appear to have been any accurate blueprints to work from! The more I look at original Lotus parts (cylinder heads in particular) the more I realise this! Follower bore positions sometimes are off in two axes too!

I'm sure the SAS head is very good though. What brand of cams are you using, and are they made from blanks, or regrinds?

[HCA]

But is this maybe a fault across this rather closed industry at the time and not peculiar to Lotus?

I have of late taken an interest in the various relationships of the day, particularly Ford with Lotus and Cosworth and find it amazing the speed of many developments, and the number of players tumbling in. Was there any time for such niceties as keeping detailed blueprints or carrying out quality control?!

Re my head - do not get me wrong, it, to me, looks superb. It is an SAS head that I bought from John Wilcox as 'his' head. But if you look at Tony Ingram's 'own' head, it is identical in spec? ported and polished 45 with 38 throttles etc. The cams are Kent D144 purchased new from Kent direct.