Vale timing and clearances - symptoms

#1
Hi guys,
I have just adjusted the valve timing on my 2000TC which was a bit off. I'd hoped this would be the panacea to the car's serious lack of power and chugging engine note but it has made little difference. I've checked the clearances and they are a fair bit off, and yet she idles nicely but just has no power at all. I have checked, rechecked, and rerechecked the usual suspects - timing, carbs, HTs, plug, compression. Are my symptoms typical of clearances being out? (sorry, I don't have them to hand, but some are tight, i.e no clearance, some 5 thou out).
 
#2
roverrocket said:
Hi guys,
I have just adjusted the valve timing on my 2000TC which was a bit off. I'd hoped this would be the panacea to the car's serious lack of power and chugging engine note but it has made little difference. I've checked the clearances and they are a fair bit off, and yet she idles nicely but just has no power at all. I have checked, rechecked, and rerechecked the usual suspects - timing, carbs, HTs, plug, compression. Are my symptoms typical of clearances being out? (sorry, I don't have them to hand, but some are tight, i.e no clearance, some 5 thou out).
Also forgot to add that the car runs better at >10degrees advanced rather than the book figure. The timing marks appear accurate as I've found TDC with the screwdriver test
 
#3
You'll never get it to run right with the valve clearances off like that. Symptoms are normally ( on mine anyway ) a lumpy tickover and a serious lack of power. Mine struggled to do 40mph on a motorway with my foot welded to the floor ! A "sloshy" exhaust note as well.

The job is long and is a lot more involved than on an OHV engine as the camshaft needs to be removed, which is why presumably they don't get done. Most people think the tappets need setting only when they are noisy. But on this engine they go quieter when they need doing !

I chose to remove the cylinder head at the same time and was glad I did as it was on the points of failing between the rear two cylinders. If you go down this route make sure to change the block to head oil seal 'o' ring.

Here are my posts from when I did this job viewtopic.php?f=21&t=13354

On the plus side it will absolutely transform your car.

PS I've never had any joy with the book timing figure. When I set this the car's performance is poor. I put this down to modern petrol so you need to experiment a little to find the best setting for your car. 10 Degrees is a good starting point.
 
#4
pat180269 said:
You'll never get it to run right with the valve clearances off like that. Symptoms are normally ( on mine anyway ) a lumpy tickover and a serious lack of power. Mine struggled to do 40mph on a motorway with my foot welded to the floor ! A "sloshy" exhaust note as well.

The job is long and is a lot more involved than on an OHV engine as the camshaft needs to be removed, which is why presumably they don't get done. Most people think the tappets need setting only when they are noisy. But on this engine they go quieter when they need doing !

I chose to remove the cylinder head at the same time and was glad I did as it was on the points of failing between the rear two cylinders. If you go down this route make sure to change the block to head oil seal 'o' ring.

Here are my posts from when I did this job viewtopic.php?f=21&t=13354

On the plus side it will absolutely transform your car.

PS I've never had any joy with the book timing figure. When I set this the car's performance is poor. I put this down to modern petrol so you need to experiment a little to find the best setting for your car. 10 Degrees is a good starting point.

Thanks for that, I'd better brace for the hours in the cold garage. Any idea where I can obtain the shims? Your symptoms sound like mine only more severe - I can hit 80 but that's after a massive build up. A slight gradient will kill her and she sounds hoarse and unpleasant. The puzzling thing is she has had an unleaded conversion in the recent past and was running fine a couple of years ago (and only a few thousand miles) according to previous owners.
 

Dave3066

Well-Known Member
#5
I did my valve clearances last year. Here's a link to my post on the subject, about half way down this page Valve Clearances

Symptoms before were a splashy, erratic exhaust note and a general lack of ooomph! The trick is knowing what size shims you have fitted before you order replacements. If like me you use your car all the time you won't be able to afford the time or effort to remove the camshaft to measure the shims you have fitted so I did it when I had the head off, knowing I was going to re-shim at a later date. I also made a note of the shims I fitted afterwards so if I need to do the job again I have a point of reference. Most important when doing this to remove the head bolts in the correct order to prevent undue stress on the camshaft. I haven't seen one snap but I've heard it can happen :|

A few of us have quite a good selection of shims to choose from so if you know what sizes you're after post it up here and we'll see if we can help.

Dave
 
#6
As Dave says you need to know the gap for each valve and also the shim size currently fitted. Measure the gaps a couple of times to make sure and write them down. The problem I found is if you can't get a feeler gauge in you can't measure the gap because there isn't one !

Regarding shims, you can often swap shims about to minimise the number you have to buy. I got mine from Mark Gray ( www.roverp6cars.com) but others on here will be able to help.

If you are going to remove the head you can shim the valves on the bench before refitting the head as described here viewtopic.php?f=2&t=16289 part way down, using some studding nuts bolts and washers.
 
#8
I still haven't got round to doing the clearances. I have adjusted the valve timing which was a fair bit out but with no discernible difference in driving performance. I've concluded that adjusting the clearances won't make a huge difference either
 

harveyp6

Well-Known Member
#9
roverrocket said:
Are my symptoms typical of clearances being out? (sorry, I don't have them to hand, but some are tight, i.e no clearance, some 5 thou out).
roverrocket said:
I've concluded that adjusting the clearances won't make a huge difference either
There speaks the expert. I look forward to your continuing input.
 

Dave3066

Well-Known Member
#10
roverrocket said:
I've concluded that adjusting the clearances won't make a huge difference either
Based on my own experience I have to disagree. IMO It's pretty vital to have the valve clearances within specified limits if you want to get the most out of your engine. Think about it this way, if the clearances are tight, as you've said some having no clearance, then you may be losing compression due to a valve being every so slightly off its seat. Something akin to the symptoms I had recently with a burnt exhaust valve. The engine runs a bit rough and is down on power but it still runs.

Dave
 
#11
Valve clearance has a major effect on valve timing. It depends on the particular camshaft profile and valve gear geometry, but each thousandth of wrong clearance can be equal to several degrees of timing. Too little clearance, the valve opens early and closes late. Too much and the reverse occurs.

Yours
Vern
 
#12
roverrocket said:
I have adjusted the valve timing which was a fair bit out but with no discernible difference in driving performance. I've concluded that adjusting the clearances won't make a huge difference either
It will trust me, I'm not a doctor, but believe me it will. :D

Before I started the work my exhaust valves clearances were as follows

( FRONT)0,0,11,(REAR)0

As Dave says with zero there is a chance the exhaust valve will be held open with loss of compression, in my case on 3 cylinders !

My car was quite simply the worst drive imaginable, no power whatsoever, stalling at every junction unless I danced on the pedals; a gutless pig I didn't want to drive more than a few miles.

Now engine is smooth and powerful, eager to rev and ticks over at 650-700rpm. It really was night and day.
 
#13
I have to say I believe valve clearances were engineered for a reason, and I accept those engineers who know more than I do.
On the off-subject comments: There is a great wealth of experience represented in this forum, and you cannot buy that anywhere. I only wish I had a similar resource to consult with in my line of work where I am often left on my own to figure it out.
 
#14
Hi,

Running, especially an exhaust valve, with zero valve clearance will almost invariably result in it burning out. This is because without period contact with the relatively cool valve seat the head of the valve will struggle to loose heat and eventually burn. You need to get this sorted before the job gets even bigger :oops:

Tim
 
#15
I have to say I believe valve clearances were engineered for a reason
Yes you're right. If there was no gap as the engine warmed up the valves could be held open as parts expand. The shims allow the gap to be set accurately which takes out production tolerances in the cylinder head, valves and valve seats. As someone else mentioned the gap is an integral part of the valve timing.The point made about the cooling effect of the valve on its seat is also important. If the valve is held open heat cannot be conducted away, via the seat and cylinder head water cooling, and it will overheat and burn out.
 

redrover

Active Member
#16
I think Tim (KMan1600) and Pat have hit the valve on the head. :wink: The valve clearances are precisely set for a reason - or rather, for a variety of reasons.

Regarding thermal expansion, yes, valves grow - especially exhaust valves - when the heat of the combustion (and exhaust gases bathing the open valve stem) cause the steel to expand and the clearance to become smaller. But they don't grow by 13-15 thou! IN FACT, I know from my own experience - which I accept is neither comprehensive nor conclusive, but which was gathered from repeated clearance comparison tests between the engine at stone stone cold, and after completing multiple 100-mile motorway trips - that the valve clearance in a P6 four-cylinder GROWS by almost precisely 1 thou, for both inlet and exhaust across all cylinders. To my mind, this indicates that the thermal expansion coefficient of the cast-iron camshaft carrier is greater than that of the valve/shim/bucket assemblies by a difference of +0.001 thou, to the extent that additional clearance is generated. Precisely why the exhausts don't appear to grow by a greater degree than the inlets left me a bit flummoxed, but my initial thoughts were that the valve seat grows to offset the relative growth of the exhaust valve. Or something like that. That's pure speculation, but an interesting point of discussion....

Back on the main point....

The clearance also allows a fine adjustment tolerance to govern the precise moment and extent of the valve's opening event, as Tim and Pat say. Which allows you to compensate for wear (majority of cases) or machining (in my case).
But in reality, they're there to make the valve train more durable over the course of its life in the hands of an ordinary motorist, by leaving a 'slack space'.

Can you get away with tighter clearances? Yes. I intentionally have my exhausts set to 10 thou, and they haven't moved in 5,000 miles, and I've even had the head off to inspect when the (poorly remanufactured) O-ring failed. But that's with new valves and seats. If they last 15 years, I'll be happy. But I wouldn't risk an older valve train. Without fully dismantling it, there's no way of knowing what state the valve faces or lands are in, or how brittle the seats/valve heads may have become. If it's tighter than 8 thou, I'd feel happier if I started collecting parts.

But that said.... if tight clearances are present, I'd also want to address the cause as best I could. Is the engine running on? Are the cooling ways in the head a bit furred up? Is it pinking under load, or running lean at speed? All of these things will only accelerate a valve burning out by generating excessive heat in the combustion chambers.

Tight clearances is a symptom as well as a problem. There are a variety of potential causes behind it, and somewhere in that may also lie the solution to your poor performance issue.

Michael
 
#17
Thank you for all the useful information. Although Rockdemon, while i agree any grievances should go via the proper channels, I do feel the public grief you refer to was rather coming the other way. Fortunately, and overwhelmingly, this excellent forum is willing to be patient and not condescending to a newcomer to the classic car world in general, and P6 world in particular. I take on board your invaluable advice and I will be tentatively starting the reshim this weekend. Results to follow!
 
#18
Sorry Michael I didn't answer your questions. Yes, she was lean at higher revs but no pinking. The curious part is that, while driving like a pig, she idles very nicely and evenly. Reading valve-related posts on here it would seem people are suffering farther out clearances than me, yet have a driveable car. I am satisfied all other potential culprits have been addressed. Again, thanks for all the input.
 
#19
I fear you haven't quite taken the point on board, roverrocket. The object of the exercise is NOT to minimise the valve clearances. We are seeking to get them just right when the engine is at operating temperature. Clearances are checked and set with the engine cold. The combination of the general mass of the engine warming up somewhat and the valves warming up a lot leads to the clearance as measured reducing. If you start out with no clearance then at operating temperature the valve is held open.

Rover engines tend to reduced valve clearances as they wear and the heat of running further exacerbates this. Tight clearances are a problem. Loose clearances are not.

Chris
 
#20
Hi chris,
Sorry by farther out I meant a deviation from where they should be, not simply a larger gap - im aware a wrong clearance is either side of the manufacturer's figures.
 
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