How tight is right

lyons · Post by **lyons** » Sat Jan 10, 2015 3:50 pm

To all those who have built cylinder heads before - I have installed both cams with new oiled bearings and torqued to 15lb/ft.

However while the inlet side turns easyily by hand, the exhaust will turn smoothly but only after assistance with a lever between two inserted bolts in the cam drive.

Is this OK and will it free up when the engine runs.

mike837go · Post by **mike837go** » Sat Jan 10, 2015 5:12 pm

No, it is not ok.

Both sides should behave the same way.

Little to no resistance from the bearings. It should take a solid grip on the end of the shaft to overcome the valve springs.

Go back and double-check that the valves move freely, the springs are not work hardened, the cups move freely, the shims stayed in place, etc.

There is a problem. Fix it now. Not when you are trying to chase down a hard start or rough idle condition.

Post by **mgcjag** » Sat Jan 10, 2015 5:26 pm

Hi Lyons.....just to clarify is the head off the car.....in either case the cams should not be turned individually as the valves could clash and bend......also with the head on the bench it should have supports underneath so the valves do not hit the bench....these supports are detailed in the manual.....please come back and let us know what position u are in....Steve

abowie · Post by **abowie** » Sat Jan 10, 2015 10:36 pm

I'm assuming that (a) you have the head off the car and (b) you don't have the valves and springs fitted, as I doubt anyone could turn a cam by hand alone if the springs were in.

Given the above I agree with Mike; both should be the same. I have built a number of heads but am embarrassed to admit that I've never just put the cams in on a bare head and turned them to see what they feel like.

Have you put in a new set of cam bearings? If not, do so and see if it makes the resistance equal. If so, there is something wrong with one of your cams.

Alty Ian · Post by **Alty Ian** » Sat Jan 10, 2015 10:42 pm

Sounds like he has fitted the valves and springs before torquing up the head.

In which case if you turn one cam independently of the other (which the manual tells you NOT to do) the exhaust valve may well hamper smooth turning of that cam on the cylinder where the inlet valve is already open.

I suggest you carefully check your valves now before doing anything else.

johnney · Post by **johnney** » Sun Jan 11, 2015 4:38 am

Check you have the bearing caps in their correct positions.

Moeregaard · Post by **Moeregaard** » Sun Jan 11, 2015 5:30 am

If the head has been skimmed, the align-bore of the cam journals should be checked before assembly.

lyons · Post by **lyons** » Sun Jan 11, 2015 10:31 am

Sorry Guys.

Should have mentioned that the the head is on the bench with no valves or valve springs fitted, so cams in head just to try for free movement.

Head has been skimmed with 0.10 thou taken off.

New bearings and caps are all in the right place.

All my books state 15ft/lb, is this correct as data tab from classic car engines states 9 ft/lb

Post by **mgcjag** » Sun Jan 11, 2015 10:57 am

Hi Lyons......from one of your previous posts u were asking about cams to fit different heads.......so whar are u using now......were the caps with the head and different cams fitted.......Steve

lyons · Post by **lyons** » Sun Jan 11, 2015 12:52 pm

Steve,
Well spotted.

Given the choice of either XJ6 4 hole cams, I decided to use 2 hole cams from S'type in XJ6 s2 head.

It seems that all works fine with all the original caps in place but reason to try cams without springs or valves was to try and fit the one long end cam cap that goes with tach generator on the inlet side and that is when it goes tight. Would not have believed that it would make such a difference even with new shells.

Engine is for 3.8 E type so guess another solution ie electric tach may be the way forward.

abowie · Post by **abowie** » Sun Jan 11, 2015 8:01 pm

lyons wrote:
All my books state 15ft/lb

This is correct.

David Oslo · Post by **David Oslo** » Sun Jan 11, 2015 9:37 pm

So it's the one "foreigner" cap that causes the problem. And you want to fit that in order to get the tacho to work. Hmm, I know it's not proper engineering, but what about using metal shims under the offending cap to get the upper part of the new shell bearing out of being over-tight. We're propably talking around 3 to 5 thou. A set of feeler gauges could sacrifice one of their blades to make the shims. Still allows you to tighten down metal-to-metal to the required torque.

christopher storey · Post by **christopher storey** » Sun Jan 11, 2015 10:16 pm

The caps are all matched to the individual head when the engine is first made . The only way to get a non-original cap to fit is to have the assembly line-bored, but it is still a compromise which may not be satisfactory. Under no circumstances whatsoever must the caps be shimmed, as this is likely to result in whip in the camshaft which will break in no time at all, with catastrophic consequences for the engine

abowie · Post by **abowie** » Mon Jan 12, 2015 4:39 am

lyons wrote:Steve,

Engine is for 3.8 E type so guess another solution ie electric tach may be the way forward.

I did this on my 3.8. I left the tach generator in situ without the drive dog, as a dummy. Sort of reverse to your situation but works fine.
Tach conversion isn't complex.

PeterCrespin · Post by **PeterCrespin** » Mon Jan 12, 2015 6:20 pm

lyons wrote:
Would not have believed that it would make such a difference even with new shells.

Now you know. More likely to make a difference with new than old shells. Ten out of ten for checking the free-spinning fit and ten out of ten for misplaced optimism that you'd get away with it. Didn't hurt to try, but...

JEP41 · Post by **JEP41** » Tue Jan 13, 2015 5:27 am

This is an interesting problem, my 3.8 litre E-Type manual also states torque the cam bearing caps to 15ft/lbs. My 3.8 litre MK2 manual states torque the cam bearing caps to 9ft/lbs. From this I would assume the B series head should be 9ft/lbs. and the straight port head 15ft/lbs. I had the same problem as you with one cam just slightly tight at 15ft/lbs. on my C-Type replica engine which has a B Type head fitted. I re-torqued to 9ft/lbs. and all was perfect both cams turned freely with the same feel. This engine has since run on my test bed and performed excellently

PeterCrespin · Post by **PeterCrespin** » Tue Jan 13, 2015 2:36 pm

They all spun freely at Browns Lane but 50 years later a thou or two of warpage can sometimes be expected. It doesn't show up until you fit new shells which have not settled in with the head and cams over the decades. Of course a new shell can be out as well or a speck of dirt of white metal out of place.

I think the biggest reason is heads being imperfectly checked/straightened before skimming. The answer to a warped head is not the same for an OHC head as it is for a pushrod head and straightening a big casting like an XK head is a blacksmith job of heating, over-bending then bending back etc. not everyone bothers and even the best shops might still be out by a thou. This doesn't matter for a head gasket but could affect a cam with new snug shells. Once the face is skimmed the distortion is fixed relative to the new datum line but so long as it's only finger tight it should be OK. Anyone needing a lever to turn a bare cam should get it line-bored.

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