Valve tappets and shims - pain in the @$$

[leifanten]

I am in the process of adjusting valve clearances now that I have repaired the water pump. I have got all but one perfectly within their respective tolerances. However, the last one is causing me some consternation. It is #3 exhaust, and even without shims in place there is no gap to the cam. I have done some measuring and it turns out that the gap between the spring retainer plate/disk and the cam is 121 thou whereas the thickness of the tappet/bucket at the corresponding measurement is 185. That explains why no shims did any difference, the tappet was resting on the spring retainer and not on the shim & valve stem. Basically, the tappet is 64 thou too thick.

There was a shim in place when the engine was running, so the interesting scenario of what would happen if one were to run it sans shim (valve loosing grip to valve retainers and bye bye) did not occur.

Has anyone had similar issues? And does anyone have valve buckets of approx 120 or less thickness lying around that I could purchase. Otherwise I would need to get my current bucket ground down by 65+ thou at a machine shop.

The engine was running very strong before the water pump bust, and I think it has not run long enough to have burned the valve (less than 100 miles since rebuild by P.O)

[rgh0]

Leif

There is something very wrong for one valve to be giving you this problem.

I suspect the retainer has started to pull through the collets on the valve stem. This may be due to use of non properly matching parts if the engine was rebuilt oly 100 miles ago. Does no3 exhaust valve have a deeper hole in the retainer until you reach the valve stem tip than the other valves - i.e the retainer is located higher on the valve stem. This will confirm that problem

If it is this you you need to dismantle the head and check that correct parts have been used and problable replace some incorrect parts

cheers
Rohan

[leifanten]

Rohan,
thanks for your reply. I have the head on the bench and it is easy to inspect all of it. It would seem like #3 exhaust valve sits a little deeper in its seat, to the tune of 20-30 thou. This would explain some of the discrepancy. Also the cam follower (tappet) has a thicker wall than the other exhaust followers to the tune of about 30 thou (185 vs 155 for the others) That would cover the rest of the discrepancy. Further, it would seem that this thicker wall comes from it not having had the groove turned as deep as the others, since the thickness in the center section that rests on the shim is only about 7 thou thicker than the thinnest part, where others are 65 thou thicker in this place.

The valve sits well in its seat (albeit slightly deeper as mentioned) and the retaining ring and locks are as they are supposed to be.

Comparing the follower to the others, I think that is where the core of the problem is. I am thinking I could turn the groove in the #3 follower deeper to the same tune, I.e. to a point where the thickness in the thinnest part is 120thou and the center section remains at 192 thou, which gives a difference of 72 thou and the need to shim up with 61 thou shim to give a 9 thou lash.

CURRENT:
shim 134 (this would be the shim required to hit the high point in the center of the follower)
center added thickness 7
perimeter thickness 185
lash -64 (negative lash)
sum 262 valve stem to cam


TARGET:
shim 60
center added thickness 72
perimiter thickness 120
lash 9
sum 262 valve stem to cam

This would give a minimum thickness that is 35 thou less than the other followers, which will make it a little weaker. The other alternative would be to turn it down to 155 and reseat the valve.

[alan]

Hi ,
i had a problem like this many years ago. The shims were touching the valve spring retainers and not the end of the valve stems. This meant everytime the cam turned it released the grip of the collets on the valve stem. The shim when in place should act on the end of the valve stem and not the machined recess in the valve spring retainer. If it acts on the valve spring retainer it wil loosen and tighten the collets on the valve stem everytime the cam operates.
I fitted new collets and new spring/collet retainers and it corrected the problem. I think the p.o. had fitted the wrong collets and retainers or really hammered and overreved the engine before.
I hope this is of help
Alan

[rgh0]

Hi Leif

You can buy thin steel cam bucket followers that may solve your problem. I would do this rather than try to machine your existing one ( I presume it is a cast iron original type). The buckets are hardened and will need to be ground and this will be very hard to do on the inside

It worries me though that this has just been a problem with the original assembly since the engine was built and can be fixed with a thin bucket. If this was the case you were very very lucky that it all stayed in place for 100 miles. Any half competent builder would pick up the problem of no clearance when fitting the cams and shims and if this problem was not picked up the rest of the head and engine may be a disaster also. Lifting the valve by pushing down on the valve spring retainer rather than shim and valve top would normally have resulted in the collets coming loose or at least having a very good hammering and getting damaged.

I would dismantle the springs and valves and check all the components carefully before reassembly.

Personally I would also strip check and reassemble the rest of the engine now that the head and water pump are off to make sure no other major problems but you may not want to go to that extent if the bottom end appears OK

cheers
Rohan

[leifanten]

Thanks.
Alan, the shim does touch the end of the valve stem. However in order to make contact between the valve stem through the shim and onto the cam follower in order for the follower not to be in contact with the spring retainer the cam is in constant contact with the follower to the tune of 60-65 thou compression when in completely closed position on the cam lobe.

Rohan, you are describing my concerns well. I have had a couple of WTF moments when I have been re-restoring the car (which has been in dry storage for >20 years after its previous restoration). Another couple of examples have been that none of the valve shims had been replaced and that only two valves had correct gaps and that the diaphragm in the stromberg was mounted back to front with the air valve piston also facing the wrong way. Anyway, I digress. I had the sump off when doing the water pump and got a good chance of inspecting the bottom end. It looked fine from a visual inspection.

I am trying to find out the two thickness measures of the "pad" on the thinner steel followers, and hope that it will solve my problem. Grinding the inside of the hardened original one is not a simple task, and I would need to find a machine shop that could help me out with a lathe (and I am also concerned that grinding through the outer surface will cause the hardening go be gone afterwards, since I do not know if it is hardened all the way through or only surface hardened)

I have driven the car after rebuilding the carbs and tuning ignition etc and it has no noise from the bottom end and pulls very strong on all gears (at least up to 3000 rpm since I am running it in, I have not gone above that). I may be a victim of wishful thinking, but I would say the bottom end is good.

[alexblack13]

Hi Leif,
Rohan is very right. You really should do as he says. The worrying thing for me would be the way the engine was assembled by PO? You now have 1st hand evidence of his 'work'. I would look very carefully at the rest of the engine. If you still have the sump off take out the pistons and examine carefully. Then take off the main caps and examine the bearings etc. With any luck the mains will be fine. Renew the big end shells if any doubt. Hopefully pistons and bores will be within limits but check the ring gaps.Any wear? replace the rings at least. When you have done this you will feel better and know the bottom end is fine. I would then have the head overhauled with new seats and guides at least. You should not be using shims much less than 070'' thick. And do not grind the valve stems to get clearance. I am betting this is what has been done here.

Something is well up with #3 exh' as you know. Got to be sorted!! Helps you sleep at night.

Best wishes. Hope you get is sussed and fixed soon.

Alex...

[rgh0]

Hi Leif

I would not attempt to machine or grind new cam followers as they are all nitrided steel and once you go through this layer you compromise their strength and hardness plus they are all very thin to begin with and any reduction in thickness may compromise their strength. Similarly machining the original chilled cast iron followers will reduce their strength and risk falure. All the followers are around 60 Rockwell hardness and very difficult to machine without specialist grinding equipment anyway.

I measured up some sets of followers with results as follows

Dave Bean - wall 2.4mm - pad added thickness 1.1 mm
Elan factory set 1 - wall 3.2mm - pad added thickness 0.3 mm
Elan Factory set 2 - wall 3.2mm - pad added thickness 1.3 mm
Original cast Iron - wall 3.6mm - pad added thickness 1.9 mm
All of these dimensions had a tolerance of around 0.1mm across the set of 8

You may find a racing type follower that meets your needs but i think you really need to solve the root cause problem of incorrect location of the No3 ex valve and retainer. The other vlaves may have had things done to them to get adequate clearances and this may affect the long term durability of the engine. i would dismantle and examine and measure all valve train components and set it up back to standard
cheers
Rohan

[leifanten]

Alex/Rohan, I took out the valve and compared to a set of unground spare that I have. You are right , the valve stem has been ground about 0.3mm to make the clearance. I put in the valve that has not been re-faced, and with an 80 thou shim I got a 10 thou clearance. This was just an experiment, as this valve is not ground to fit the seat of the head, but I just wanted to seek the cause of the problem.

It would appear that the root cause of this for this is that the cam follower is manufactured way off spec compared with Rohan?s measurements as well as to the rest of my set. This one is 4.7mm thick and the pad adds only 0.18mm. (Seems like the man at the lathe at the Lotus plant was late for his favourite supper that day ) This means that if I had a David Bean follower I would have had 0.76 mm (30thou) of base clearance and even with the Elan factory sets of Rohan I would have had a 3thou base clearance (still not acceptable, but better than a 60 thou negative clearance).

The bottom end has new +030 pistons and the cylinders has no wear edge from the rings at all. I still think I might pull the sump off again to inspect the bearings and make sure the torque is right. I don?t have a lift in my current place, and I am looking forward to balancing four bolts, a sump, two gaskets and a ratchet on my chest again.....

[rgh0]

If you need racing followers with a standard engine then you either have to long valve stems or the valves are badly recessed.

Standard valves should be

Inlet 3.90 inch long
Exhaust 3.85 inch long

and fit with shim of around 120 thou with a follower of 220 thou thickness if the valves are in the right position in the head and not recessed

cheers
Rohan

[andyelan]

Hi Leif

While I appreicate what you said was probably just said in fun, please don't blame Lotus for the incorrect cam follower you have, I would very much doubt that your particular item has ever been anywhere near the Lotus factory.

The cam followers used for the Twin Cam are very similar to those used in the British Leyland O-series engine, the Jaguar XK engine and various Coventry Climax race engines and as such would be bought-in items. I actually find it incredible however to think that a relatively simple but presision component like a cam follower could have been manufactured incorrectly in the first place. I would suggest it's much more likely that it is "correct" but intended for an application other than the Lotus Twin Cam.

Regards
Andy

[rgh0]

Just to add to Andy's comment

There are a number of oversize in diameter tappets from other applications that may be fitted by boring out the sleeve if the sleeve is worn and you dont want to replace it ( I have heard of Alfa and Cosworth ones being used for example). Maybe this unusual thickness tappet was substitued due to bore wear - check its diameter versus the others fitted and the standard specifications



cheers
Rohan