Standard camshaft max lift

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Rich70
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#1 Standard camshaft max lift

Post by Rich70 » Wed Feb 12, 2020 6:33 pm

Hi all,

Can anyone confirm if the maximum lift on the standard 4.2L camshaft is 110 degrees for both inlet and exhaust?

The engine is in a S2.

Thanks in advance.
Richard. UK RHD 1970 S2 2+2 Auto.

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MarekH
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#2 Re: Standard camshaft max lift

Post by MarekH » Wed Feb 12, 2020 8:07 pm

I'm not sure I even understand what you are talking about.

The maximum amount of lift will be bounded by one of two things:- will the locking collets on the valve stem slap into the the valve stem seal; will the valve be pushed down so far that it hits a piston given its relationship with the crank.

Only the latter is affected by how long the valve is open, but that is not necessarily symmetrical about crank tdc, so your question also has to consider cam timing.

That's why I made low profile teflon valve stem seals for my engine.

kind regards
Marek

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abowie
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#3 Re: Standard camshaft max lift

Post by abowie » Wed Feb 12, 2020 8:13 pm

Marek I think he's asking what the timing is when the valve is maximally open.

I'm not sure I can calculate this without some thought but Std S2 cam 0.375" lift, duration 256 degrees, timing is 17/59 59/17.
Andrew.
881824, 1E21538. 889457..oops. Jezza the V12 XJS race car.
http://www.projectetype.com/index.php/the-blog.html
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Rich70
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#4 Re: Standard camshaft max lift

Post by Rich70 » Thu Feb 13, 2020 7:31 am

Sorry for not being clear in the question Marek but Abowie is correct in his response. I was looking for the degree at which the valves are open at their maximum lift.

Some simple maths identifies the answer:
59-17 / 2 + 90 = 111 degrees.

Ill dial in the camshafts at this point.

Thanks all! Rich
Richard. UK RHD 1970 S2 2+2 Auto.

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mgcjag
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#5 Re: Standard camshaft max lift

Post by mgcjag » Thu Feb 13, 2020 8:38 am

Hi Rich...what are you actually trying to do.....you dont need his info to set the cam timeing....Steve
Steve
1969 S2 2+2 & Building a C type replica

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#6 Re: Standard camshaft max lift

Post by abowie » Thu Feb 13, 2020 8:58 am

mgcjag wrote:
Thu Feb 13, 2020 8:38 am
Hi Rich...what are you actually trying to do.....you dont need his info to set the cam timeing....Steve
What Steve is alluding to is that the cams have a slot in them that allows you to fit a cam timing tool that will dial them in for you.
Andrew.
881824, 1E21538. 889457..oops. Jezza the V12 XJS race car.
http://www.projectetype.com/index.php/the-blog.html
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#7 Re: Standard camshaft max lift

Post by mgcjag » Thu Feb 13, 2020 10:28 am

Hi Andrew is the cam timing not 15/57.....Steve
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1969 S2 2+2 & Building a C type replica

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#8 Re: Standard camshaft max lift

Post by abowie » Thu Feb 13, 2020 12:08 pm

That was the only figures I had for a S2 cam but I am happy to be corrected.
Andrew.
881824, 1E21538. 889457..oops. Jezza the V12 XJS race car.
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Adelaide, Australia

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#9 Re: Standard camshaft max lift

Post by mgcjag » Thu Feb 13, 2020 12:38 pm

Hi Andrew..im not sure......the 3.8 section of the manual has 15/57..i cant see a change in the 4.2 sections..although the cam profiles were changed ..i thought they kept the same timing.....anyone else know for sure....Steve
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#10 Re: Standard camshaft max lift

Post by PeterCrespin » Thu Feb 13, 2020 6:25 pm

Degreeing the cams depends on tappet clearances. Using max lift doesn’t.
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Bob.
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#11 Re: Standard camshaft max lift

Post by Bob. » Thu Feb 13, 2020 6:58 pm

S3 V12 cams are 17,59;59,17, perhaps that's where the change was made.
Bob
'71 S3

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#12 Re: Standard camshaft max lift

Post by christopher storey » Fri Feb 14, 2020 11:11 am

The camshaft timing was altered from 15/57/57/15 which had been used from XK120 days, in about 1968/9, for emission control purposes . I cannot now remember how much alteration was applied but it looks like 2 degrees of crank. I also have a feeling that this coincided with the alteration to tappet clearances but someone else may comment

PS I do not recall the duration being altered from 252 to 256

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#13 Re: Standard camshaft max lift

Post by mgcjag » Fri Feb 14, 2020 1:36 pm

Hi All...just looked up the Service bulletins...when the camshafts were changes to the ones with the grove and revised tappet clearances of 12-14 the timing was also changed to 17/59
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#14 Re: Standard camshaft max lift

Post by John ball » Fri Feb 14, 2020 6:18 pm

While on the subject of camshafts, please can someone explain to me what they think are the duration degrees for the Rob Beere camshaft I have in my XK120. It is listed as RBCSU, with a duration of 235degrees ??!!
which apparently is designed for the XK engine to give good torque ? I have asked Rob Beere and he does not appear to know the inlet exhaust degrees and I cannot work out how to get to the figures. It is obviously not 15/57/57/15 or 17/59/59/17. I also asked Kent cams who make them for Rob Beere and they could not answer my question ?
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#15 Re: Standard camshaft max lift

Post by mgcjag » Fri Feb 14, 2020 7:25 pm

Could be a typo in the list...if its a kent cam i cant see why they dont list it or know the spec....I would also think the Rob Beere are 4.2 cams.......are they the same as you 3.4? Cams.....is there a profile number on your cam or do you have the invoice with details....Steve
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#16 Re: Standard camshaft max lift

Post by abowie » Fri Feb 14, 2020 10:03 pm

Duration is just 180 + (opening degrees) +(closing degrees) so if they give you those figures it might help.

It's also possible that the quoted duration is not total duration but duration at 50 thou lift.

I am the first to admit that I do not fully understand camshafts but issues such as valve crossover time and asymmetrical timing will affect torque as much if not more than total duration.
Andrew.
881824, 1E21538. 889457..oops. Jezza the V12 XJS race car.
http://www.projectetype.com/index.php/the-blog.html
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#17 Re: Standard camshaft max lift

Post by Tom W » Sat Feb 15, 2020 9:26 am

John, 235 degrees does sound like a typo on the Rob Beere website. I would expect somewhere between 252 and 282 of the cams above and below. I’m surprised Rob or Kent cams can’t qualify the duration. This is inherent in the cam design for a given valve clearance.

The point at which the valves open and close is dependent on how the engine is built as well as camshaft choice, so unless Rob built your engine, he’d have no way of knowing. If you use the standard cam timing tool, you get a known timing for a given cam, but you can deviate from this. Rob Beere makes a setting tool with 4 different options, only one being standard. So whilst you can’t change the total duration, you can, for example open the inlet earlier at the expense of closing it earlier.

As the XK engine is a twin cam design, overlap is also dependent on how the engine is built, as well as cam duration. Jaguar used identical duration for both inlet and exhaust cams, and timed them symmetrically, but there is the opportunity to time the cams differently.

There are lots of opportunities to change things, and in theory improve certain attributes, usually at the expense of making something else worse. The trick is to make sure the improvements are in an area you care about, and the negatives only affect things you don’t care about.

If you don’t have a data sheet, you could measure what your cam timing is with a timing dial and a DTI. Without knowing what’s in the rest of the engine though, I wouldn’t go changing things. You don’t know how close valves are getting to pistons, or how close the valve springs are to coil binding.
Tom
1970 S2 FHC

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#18 Re: Standard camshaft max lift

Post by John ball » Sat Feb 15, 2020 11:45 am

Steve and Tom, yes it is very frustrating. I have talked to RB and he seems unable explain the 235 number, which I agree must be a typo. I did not see any number on the cams, so when I spoke to Kent Cams they were not very helpful and just said they build them to RB’s request. I have spoken to RB on several occasions and he assures me these cams are suitable for all XK engines and designed for SU carbs to give good torque. RB did say the feeler gauge gap was to be larger than normal, but admit I can’t remember what it was when I had the cams installed. Although engine not noisy. I did discuss the cam timing and he said use the standard cam setting plate. I have seen the tool with variations, which to me look very small and wonder whether slackness in the top chain would mask any minute accuracy ?
Not really intending to measure or take cams out, but just looking for thoughts and opinions, so thanks.
Jaguar XK120 FHC and Healey 100

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#19 Re: Standard camshaft max lift

Post by Tom W » Sat Feb 15, 2020 3:47 pm

If you have slack in your timing chain, the cam timing will be both retarded, and also prone to wandering. Accurate cam timing and correct tensioning is critical to getting the most out of an engine, that’s why Jaguar specified a vernier arrangement on the drive sprockets. Over a high mileage, the timing will tend to retard as the chain stretches and the sprockets wear. A small misalignment makes a noticeable difference, and a tired engine will usually perk up by resetting the cam timing.

If the car runs well, I’d not fuss about it. Without knowing what you have in there, it’s difficult to make any any meaningful assessment of where you’ll expect to see an improvement, and where it adds compromises.
Tom
1970 S2 FHC

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