running rough

Steve C

Member
Hi, really need some help and advise here, car is p6 2000 tc

engine running rough, with a constant putt putting from the exhaust, thought it was just carbs needing balancing etc, no luck there!

just done a compression test with the following readings, 1 170, 2 175 3 180 4 100 ( did a wet test on 4 and increased the reading to 125)

checked valve settings and have the following front to back, 1 009 2 011 3 009 4 007 5 009 6 nil 7 009 8 005.

with the above readings I really am worried, and not sure what would be the best action to take.

Regards Steve.
 
All the inlet clearances (odd numbers) are OK at .009. The exhausts (even numbers) are too tight – should be .013 to .015. Valve number 6, in cylinder 3, is clearly very wrong yet that cylinder has the best compression pressure so that exhaust valve is clearly closing fully when the engine is cold, albeit only just. Cylinder 4's exhaust valve might be burnt, causing the low compression and the putt-putting from the exhaust.

If so, then all can probably be salvaged by removing the head, grinding in the valves (replacing any burnt or bady pitted ones) then, having measured the thickness of the existing shims, reassembling with the existing shims to check how much the clearances have closed up after grinding, then removing the camshaft and buckets as per the manual to fit new shims of the required thickness. Which will be the thickness of the old ones minus the amount by which the clearances are too tight. Aim for .010 inlet and .015 exhaust to give maximum leeway for future sinking of the valves into the head. If buying new exhaust valves, make sure they are TC-spec ones able to cope with unleaded fuel.

Valve number 6 with its current zero clearance will have a negative clearance with its existing shim after grinding, that is to say it won't shut properly. So it might be worth buying a shim maybe .010 thinner for it before reassembling the head, so you have a clearance to measure before ordering the whole set of new shims. Why one valve should be so drastically lacking in clearance is a mystery. I would replace all four exhaust valves regardless.

Hope that helps.

The whole valve clearance, camshaft removal etc process looks daunting and laborious but it's straightforward as long as you follow the manual. Instead of the spacer tubes, mentioned in the manual, which are used to keep the head clamped to the block while the camshaft bearing caps are absent, you can use stacks of suitably-sized washers to create the same height. The bottom washer or two might need notches cut into their outer edges to clear the dowels that locate the bearing caps.
 
Last edited:
Just to add to the above, the car still drives ok, and sounds ok except from the constant putt putting at idle,
all plugs are a decent colour, but the exhaust is very black and sooty, no mixing of oil and water and no loss of both.
 
Many thanks for that ( I think we were both typing at the same time!) I understand what you are saying ref the exhaust valves., but the difference in number 4 readings between wet and dry is not good, what could cause this ? just to add I am no mechanic in any form, but am willing to get the spanners out and try.

regards Steve
 
Yes, the wet test adds another dimension. How much oil did you squirt in? If quite a lot accumulated in the deep bowl in the middle of the piston, it would effectively reduce the size of the combustion chamber, so raising the compression ratio. And hence compression pressure. You could try the same test on the other three cylinders and see if they show similar increases.

The manual says that a 2000 TC should have 190psi compression pressure, so even your good ones are a bit low. It's possible that there's some bore or piston/piston-ring wear, but it's unlikely to be serious. With the head off you'll be able to see if there's much of a wear ridge at the top of the bore, any scoring etc. The first thing is to take the head off and see what you find. Does the car emit blue smoke and burn oil? That could point to trouble in cylinder 4, broken rings perhaps.

The poor compression in cylinder 4 will have made it impossible to set the carbs correctly for mixture and balance, which could account for the sooty exhaust. So could the fact that combustion probably won't be occurring completely in that cylinder.

My 2000 TC became very sluggish, with a very unreliable idle despite much effort at carburettor tuning, and showed compressions around 160-170. It used no oil and blew no smoke, though. I took the head off and discovered quite bad wear ridges at the tops of the bores for a 66,000-mile engine, as if previous owners had left the choke out too long on a regular basis. I eventually decided on a rebore, and took the opportunity to enlarge it to 2.2 litres. The 2200 pistons reduced the compression ratio to 9:1, so I didn't have to worry about not running it on long-gone 100-octane fuel, and the result was a torquier, smoother engine which runs really well and idles properly – even on the original SU HS8s. It was a lot of work but the result was well worth it.
 
Many thanks once again, I have got a repair manual coming in the post , when it gets here i will be following your advice and removing the head ( first time for every thing) ref oil , I put about 10/15 mils in from a syringe, --- no blue smoke or burning of oil.
 
Keep us up to speed Steve, I'll be getting into that soon. I was hoping for some guidance from a retired gentleman, but he never showed. And good info from John also, thanks.
 
If you have access to a compressor I’d do a leak down test. That’ll indicate where you might be losing compression (especially on no. 4 cylinder.
Unless you have a good quality compression tester I’d suspect issues with accuracy on the other three cylinders as I’ve seen new compression testers be wildly inaccurate out of the box.
 
Agreed on the possible inaccuracy of some compression testers. I was very depressed when I measured the compressions of my newly rebuilt engine with a new compression tester. So I tried the old one, allowing for the fact its needle was now zeroing at 30psi after a friend dropped it (he bought me the new one in recompense), and all was well. Unless the old one had always been over-reading, of course…
 
Given the low reading on cylinder four and the 25% improvement in the wet test I'd discount bad ring seal and look at the valves. could be either seats or valve guide wear. I doubt its the valve guides as you aren't seeing any smoke from oil being sucked down or pressure increase in the rocker sump etc from exhaust going up the guide which only leaves the valve seats. That may be due to the valve or the seat insert

Check that your headers aren't cracked as that can cause a putt putt.

The low readings on the first three cylinders may be due to the pistons already being replaced with low compression ones.
 
just a quick question, getting ready to get the head off, are the ball joint connectors on throttle linkage just snap on /off ? cannot find any info any where, dont want to break them .

thanks Steve.
 
Hi, There are various types used on throttle linkage on lots of cars. What do they look like? Some are plastic and just lever off but if they have been in service for a while they can get brittle and break. Other types have two little 'ears' that lift up and release the socket, others have a sleeve that slides back and does the same thing. As a further complication the ball part come in two different sizes, as I've just found out having broken a plastic type fitted on an SD1 engine and liberating a steel one from a spare manifold. Have you got a pic?

Colin
 
Colin, thanks for that, i have had the various types before, the ears, and sleeve, but this just looks like a plastic push fit, think its part number 595812, just dont want to add to my ever increasing parts list.

Steve.
 
Having cleaned off 50 years of oil and grime I found that the ball joint did have a sleeve on it, so that saved a few quid.

yesterday got the carbs off, and the manifold ( cracked in at least 2 places, will try and get it repaired).

today, got the engine pegged at the ep mark,

Now hit a problem and need some help and advice, I have removed the little cover plate, and looked inside to find there is no bolt and copper washer !!! putting my finger in I can touch the back of the tensioner and no where to put any allen key at all, did find a spring loaded sleeve in the hole which i managed to tease out, but what to do now!!

any help on this would be great

Regards Steve.
 
Later tensioners don't have the plug and allen key. Best to hold the plunger back using a cable tie(s)
 
Thanks for that, guess you mean ease the plunger back with ( screwdriver ? ) and try and slip a cable tie over it? with hands my size, i think i will have to remove the rad, just to try and see inside.

regards Steve
 
Hi, please forgive me if i am asking a very stupid question.

Ive just been and looked at my tensioner again and tried to move it back, with no luck at all, ( how much effort should it take to move it ?)

I am locked on the EP mark, top chain wheel is also locked up, my tensioner pad is just touching the chain, but not holding it under tension ( slightly slack on the tensioner side) is it strictly necessary to compress the tensioner right off the chain, my line of thought is if both are locked up , then what can move??

Standing by to be called stupid, regards Steve.
 
The tensioner won't move back much, you have to secure it where it is to stop the sliper spring and ratchet popping out when you slacken the chain.
 
ok, an hour later and 3 cut knuckles, I have managed to get a cable tie on it, done it up tight, its not moved the pad in at all , but as you say it will stop it moving out any more, hopefully head off tomorrow.

regards Steve.
 
Well the head is off !! but I have made a right royal mess of it, followed the book and advise, released the head bolts gradually in correct order, lifted out the bolts, laid them all in order etc, removed the cam shaft caps, labeled and put in order, all ok so far !! left the small cap at front and the rear plate on and gently lifted the complete cam and carrier off the head, not noticed by me until to late was that 6 of the tappets and shims lifted with it, and then dropped off !! net result I had 6 tappets and 6 shims rolling about all over the garage floor, so I now have no idea which was on which.

Regards Steve.
 
Back
Top