E Type with XJ6 Cams - chatter

[Steve1967]

Hi, some advice please from you knowledgeable types.

I have a '67 E Type roadster 4.2 but unfortunately it doesn't have the original engine but that of a '73 XJ6 4.2.

During the restoration I stumbled across a genuine 4.2 E Type head and decided to fit that, having made the appropriate adjustments to the longer block (as discussed elsewhere on here). All went well and no problem with that.

The head did not come with cams but having checked the ones from the XJ6 they were perfect, with four holes for the sprockets, not two. I spoke to a few people/suppliers and checked on here. The advice was that the cams would work perfectly but the tappet gap will need to be increased from the 4 thou range (for E Type cams) to 12-14 thou (for the XJ6 cams). The cams had new bearings and were line bored. All this seems to be fine.

The car runs well but I have significant chatter from the cams to the extent that I cant put up with it. I've checked the gaps twice, made a few minor adjustments, but no significant noise improvements. I did have one valve which was (20 thou) too short, because I had one new valve seat fitted which was not cut in sufficiently (by allegedly expert engineers!!). Ive overcome this by grinding a small step in the shim so it sits snuggly on the top of the valve stem and does not rest on the spring top. All good.

So my question.... Would it be ok to reduce the tappet clearance to a compromise between the two settings, say 10 thou or less? I guess its a larger gap in the XJ6 due to cam profile, but I cant find any data on this. If the E Type manages on such small gaps there must be little heat expansion or contraction in tolerance, (unlike a pushrod engine), so I dont understand why such a large gap is necessary with the later XJ6 cam.

Any help or advice would be appreciated. BTW all the timing chains are properly tightened and no other noise is evident from the engine, the guts of which are all new.

Thanks in advance. I do appreciate your help and guidance on this forum. Its fantastic!

Steve

[mgcjag]

Hi Steve...you have a reply to this from Peter Crespin where you posted on another thread....you obviously have a problem especially with this one valve my assumption would be that the top has been ground down. .......the xj6 cams should be set up to 12-14....this is the same as some E types..which have the parabolic cams....not sure when the change came...think around S2.....i think you need to reasses exactly what the problem is.....Steve....PM sent.....cam info here http://www.georgiajag.com/Documents/Camshafts.html

[PeterCrespin]

quote=Steve1967 post_id=144682 time=1624052209 user_id=3732] .
The car runs well but I have significant chatter from the cams to the extent that I cant put up with it..

So my question.... Would it be ok to reduce the tappet clearance to a compromise between the two settings, say 10 thou or less? I guess its a larger gap in the XJ6 due to cam profile, but I cant find any data on this. If the E Type manages on such small gaps there must be little heat expansion or contraction in tolerance, (unlike a pushrod engine), so I dont understand why such a large gap is necessary with the later XJ6 cam.
[/quote]

Not understanding stuff is why car makers give settings. You don’t have to understand that bigger gaps can give a quieter engine if the cam has gentle parabolic ramps, you just have to believe that the people who made the car know more than you or I.

Your engine seemingly has worn tappets and / or guides. So you have the choice:

Enjoy it as-is and wait for a more clear symptom to emerge if it’s something else, or

Spend a shedload on oversize tappets and machining the guides to suit, purely to arrive at a functionally equivalent engine whose mechanical sound is at a level “up with which, you can put.”