Peugeot Engines And The Damn Tappety Noises

[GLPoomobile 958]

Just wondering, is it actually possible to make an XU engine NOT sound tappety? I know that Dave Baker says that if you use his valve clearance specs then it should be pretty quiet, but is that the case?

 

I've never heard an XU engine that doesn't sound tappety, and even the V6 in the video on Youtube (the front V6 engined 205 that one of our continental members built) sounds terrible

[saveloy 8]

Mine is pretty quiet. In fact it will stay very quiet, until the carbon builds up on the valves.

But for Gawd's sake, what do you want, blood?!

[jackherer 543]

The V6 (ES not XU BTW) has hydraulic tappets so I wouldn't be surprised if it got a lot quieter once it had been run for a while.

[GLPoomobile 958]

The V6 (ES not XU BTW) has hydraulic tappets so I wouldn't be surprised if it got a lot quieter once it had been run for a while.

 

yeah, I realise the v6 is not an XU engine, just thought i'd mention it cos I didn't know if the noises were just limited to XUs or if they are all like it.

[jim21070 2]

All of mine are as quiet as mice by XU standards.

 

When setting clearances, measure cold and set to near the minimum clearance. It is a quirk of the XU (and XUD) that the clearances increase when the engine warms up.

[PumaRacing 1]

Does a large valve clearance always mean more noise than a smaller one? Under what circumstances will it affect the noise produced?

 

For bonus points, with fairly simple measuring equipment how would you go about determining the correct valve clearance for a cam, or in fact an engine, you have no data on?

[kyepan 291]

For bonus points, with fairly simple measuring equipment how would you go about determining the correct valve clearance for a cam, or in fact an engine, you have no data on?

 

ummmm.. i know this one.. does it involve a ouija board and some really strong smelling salts?

 

 

I dunno, give us a clue Dave its early on a monday man!

Edited March 26, 2007 by kyepan

[Richie-Van-GTi 70 2 Cars]

isnt the noise effect based on the angle at which the cam first contacts the valve and by measuring the cam's angles you can determine the best clearance, or something like that. Long time since I had to work out anything as pretty much everything I touch is listed somewhere.

[jim21070 2]

If it is still considered to be noisy with the right clearances then you have to suspect cam or follower wear.

 

Does a large valve clearance always mean more noise than a smaller one? Under what circumstances will it affect the noise produced?

 

For bonus points, with fairly simple measuring equipment how would you go about determining the correct valve clearance for a cam, or in fact an engine, you have no data on?

 

 

 

Puma, an interesting question you have posed. I would think that if you wanted to establish clearances from first principles you would have to ensure a minimum clearance between the cam base-circle and the follower at the worst case, say 0.1mm, and to ensure with this clearance the cam timing is correct as the clearance will determine both the cam duration and advance (I am presuming you would have these figures for the cam). Would you also take intio account the cam acceleration/deceleration ramp to ensure the valve is not being opened/closed too quickly at a chosen clearance figure.

 

Noise with increasing clearance I would guess comes from the fact that the follower cannot follow the full length of the cam accleration/deceleration ramp and this results in a very quick acceleration/deceleration near the end of the ramp resulting in noise due to shock.

[Beastie 1]

Does a large valve clearance always mean more noise than a smaller one? Under what circumstances will it affect the noise produced?

 

For bonus points, with fairly simple measuring equipment how would you go about determining the correct valve clearance for a cam, or in fact an engine, you have no data on?

 

 

A good question - and here's another one which might give a small clue:

 

Why did the AC 6 cylinder engine (the longest production run of any engine until the VW Beetle knocked it off its pedestal) make a tappety racket with .002" valve clearances up until the late thirties and yet was whisper quiet after the war and on to the early sixties with redesigned camshaft and .020" valve clearances?

[PumaRacing 1]

It is a quirk of the XU (and XUD) that the clearances increase when the engine warms up.

 

The XU and XUD behave the same as any other aluminium OHC head with steel valves. There is no quirk, at least not in this part of the engine.

[jim21070 2]

The XU and XUD behave the same as any other aluminium OHC head with steel valves. There is no quirk, at least not in this part of the engine.

 

Describing things like that as a quirk is a legacy of being brought up on all-iron pushrod engines

 

So come on then David. What is the answer to the teaser you posed us about setting valve clearances?

[PumaRacing 1]

Describing things like that as a quirk is a legacy of being brought up on all-iron pushrod engines

 

My problem is with the basic premise. On what do base the assertion that clearances increase as the engine gets hotter?

[Hilgie 16 2 Cars]

yeah, I realise the v6 is not an XU engine, just thought i'd mention it cos I didn't know if the noises were just limited to XUs or if they are all like it.

 

As said in the original topic, the V6 hadn't run for two years so the hydrolic lifters were empty. It sounded a lot better after a good run.

[Beastie 1]

...and what about engines which are famously quiet - like Rolls Royce. A typical RR valve clearance before the days of hydraulic lifters was .006 and .008 inlet and exhaust. And according to the factory service manuals checking the valve timing with the clearances so adjusted was meaningless, so a timing clearance of .025" was specified for checking the valve timing? (Royce flywheels were marked for IO, IC, EO, EC and fitters where supposed to check the condition of the camshaft by using all the flywheel marks) The "setting clearance" is a big clue as to the aspects of cam profile which particularly influence tappet noise.

[jim21070 2]

My problem is with the basic premise. On what do base the assertion that clearances increase as the engine gets hotter?

 

Understand now. My little 205D would not start in the cold last year due to tight valve clearances. (These engines are known for sinking their valves into the head and tightening up the clearances) Once a bit of warmth got into the engine it started and ran fine as the heat just opened the clearances up just enough to allow the valves to seat correctly. I proved this by finding several inlet valves had zero clearance when cold but when warm they had a little clearance.

 

In discussions about this problem on another forum (the FCF) this was reported as a common problem with XUD engines and the quirk was well known. The word was used many times in the context of valve clearances, hence my use of the word here.

Edited March 27, 2007 by jim21070

[ALEX 98 1 Cars]

If you can't stop the tappety noise by adjusting the valve clearences, then it's probably worn valve guides.

[PumaRacing 1]

Understand now. My little 205D would not start in the cold last year due to tight valve clearances. (These engines are known for sinking their valves into the head and tightening up the clearances) Once a bit of warmth got into the engine it started and ran fine as the heat just opened the clearances up just enough to allow the valves to seat correctly. I proved this by finding several inlet valves had zero clearance when cold but when warm they had a little clearance.

 

In discussions about this problem on another forum (the FCF) this was reported as a common problem with XUD engines and the quirk was well known. The word was used many times in the context of valve clearances, hence my use of the word here.

 

Ok good. Now I can answer. The question is whether the head itself or the valve train expands more as the engine gets hotter. The solution will be the same for any aluminium OHC head, Peugeot or otherwise. Whether the valves are vertical or angled doesn't affect the calculations. The reference distance is from the valve seat to the camshaft centreline. What we need to know are the temperatures involved and the coefficients of thermal expansion (CoE) of the various materials. The latter is the easy bit, the former requires either measurements or reasonable assumptions.

 

The CoEs in units of ppm (parts per million) per degree C are.

LM25 casting aluminium - 22

Cast iron - 12

EN52B valve steel - 11

21/4N valve steel - 18

 

Taking the XU engine the reference distance is about 130mm. The cylinder head is going to stabilise at somewhat above the coolant temperature although of course there'll be a temperature gradient from the combustion chamber to the cam area. If we assume about 120C on average the head will expand by about 14 thou.

 

The inlet valve (EN52B) will have a considerable temperature gradient, up to 500C at the head end at high load falling to about the oil temperature at the tip. The temperature will be heavily dependant on engine load. We can include the cam at the same temperature as the valve tip and about the same CoE. If we assume 300C for the first 30mm and 120C for the rest we get about 9 thou total expansion. If the valve head is at 500C we get about 11 thou total. So we can conclude that the inlet valve clearance will increase but the increase will be less at high load.

 

The exhaust valve is a very different story. The head end is 21/4N with its much higher CoE. The rest of the stem is EN52B. Temperatures are also much higher, maybe 650C at high load at the head. If we assume 450C for the first 30mm and 120C for the rest we get 15 thou total expansion. With the valve head at 650C that rises to 19 thou. So the clearances are going to stay about the same or slighter smaller at low load and close up by several thou at high load.

 

So that's why exhaust valves need a larger valve clearance that inlet ones in OHC engines. However they aren't going to need twice as much clearance as per the Peugeot specs which is why I use my own specs. There's basically no point in using a larger clearance than is necessary because it doesn't help anything.

 

One of the problems that needs to be considered though is the condition just after start up. The valves will heat up very quickly at the head end and for a while, until the cylinder head itself catches up, the clearances can close up on both valves which is why we need a minimum cold clearance on the inlet valve even though this will increase when the engine temp has stabilised. 6 thou is usually enough. The worst condition is if you use a stone cold engine really hard straight away. You might even use up all the normal valve clearance for a while.

 

So there you have it. No quirks I'm afraid, just maths, as is usually the case.

Edited March 27, 2007 by PumaRacing

[jim21070 2]

Wow Thanks Dave!

 

Absolutely excellent

 

Time you wrote a book methinks.

[PumaRacing 1]

I proved this by finding several inlet valves had zero clearance when cold but when warm they had a little clearance.

 

BTW, that test doesn't actually prove anything. By the time you've got the rocker cover off the valves have cooled down to the general temperature of the cylinder head. As the head has a higher CoE than the valve train the hot clearances will always be larger on both inlet and exhaust valves despite what happens when the engine is actually running which may well be the opposite. You'd have to measure within a couple of seconds of the engine being at full load to get anything meaningful and that's simply not possible except with a specially designed engine in a laboratory.

[Beastie 1]

BTW, that test doesn't actually prove anything. By the time you've got the rocker cover off the valves have cooled down to the general temperature of the cylinder head. As the head has a higher CoE than the valve train the hot clearances will always be larger on both inlet and exhaust valves despite what happens when the engine is actually running which may well be the opposite. You'd have to measure within a couple of seconds of the engine being at full load to get anything meaningful and that's simply not possible except with a specially designed engine in a laboratory.

 

It doesn't prove anything related to the point which you were making - but in context it proves Jim's point admirably. I agree also that "the hot clearances will always be larger on both inlet and exhaust valves despite what happens when the engine is actually running" However this difference can on some engines be so small as to be negligible and as a consequence valve clearances in service data sheets occasionally specify the same clearance hot or cold.

[PumaRacing 1]

It doesn't prove anything related to the point which you were making - but in context it proves Jim's point admirably.

 

Re-reading his post, I agree an engine that wouldn't easily start from cold would start better hot as the clearance increased.

 

I agree also that "the hot clearances will always be larger on both inlet and exhaust valves despite what happens when the engine is actually running" However this difference can on some engines be so small as to be negligible and as a consequence valve clearances in service data sheets occasionally specify the same clearance hot or cold.

 

Making some more assumptions and another quick play with my CoE spreadsheet. Let's assume that by the time you get the rocker cover off the cylinder head has cooled to 100C and the valves are still a tad hotter on average, 130C, as the heat is radiating out from the combustion chambers and into the coolant.

 

The head has expanded 11 thou, inlet valve 8 thou and exhaust valve 9 thou. So we're looking at about 2 to 3 thou increase in gap. If on the other hand we assume that everything has already settled to the same 100C temp we get 5 thou gap on the inlets and 4 thou on the exhausts. Trawling through my service data book there aren't many OHC engines with aluminium heads with both hot and cold clearances listed.

 

Volvo 760 Diesel

Inlet 0.20mm cold 0.25mm hot

Exhaust 0.40mm cold 0.45mm hot

 

Volvo 740 petrol

Inlet & exhaust 0.30mm cold 0.40mm hot

 

There's others but the pattern is the same, either 0.05mm (2 thou) or 0.1mm (4 thou) bigger when hot. That seems to tie in more than nicely with the theory and the maths. I guess it all depends on just how hot a recently switched off engine is and how fast you do the job and frankly that all makes it a bit of a lottery so setting things cold seems a much better idea.

 

I think it goes to prove the point though that with some knowledge of physics, mechanics and maths you can work out why something empirically tested occurs and also hopefully do the opposite - design engines and predict how they are going to behave by modelling flow, velocities, accelerations, expansions etc rather than by trial and error. That in a nutshell is why I spend so much time poring over textbooks and writing programs to simulate things before getting my hands dirty.

[Beastie 1]

Trawling through my service data book there aren't many OHC engines with aluminium heads with both hot and cold clearances listed.

 

...and to be honest I can't imagine there are any OHC engines with aluminium heads which maintain the same valve clearance hot and cold. There are a few pushrod engines with iron heads which do though. The Landrover 2.25 petrol and diesel engines are a good example: There's even a little plate on the rocker cover to confirm that the clearance is ".010" hot or cold". It's a good example of the need to look at the maths: Intuition would suggest that the clearance is going to increase when hot, but the manufacturer clearly states otherwise. Such engines did exist and it's an interesting reminder that engines have changed a lot over the years - particularly since the 1980s when interesting things started to happen once again in production automotive design. Many of the engines I deal with behave somewhat differently to modern engines and valve clearances are no exception. Firstly more modern engines have much better cooling around the valve seats and also around the valve guides. Believe it or not I once had to modify a 1920s Delage to stop it cracking exhaust valve seats: The seats were cantilevered over the edge of the water jacket so that half the valve seat was water cooled and half wasn't. Modern fuels with their high front end volatility have excascerbated this sort of problem. Secondly valve design has improved beyond all measure. Designers now understand so much more about material choice and in particular which materials work well together - not just with regard to tribology but also with regard to heat transfer: Modern valves have different materials and hardness in head, stem and valve tip. The interface between valve head and valve stem in a modern valve allows less conuctive heat transfer between the two than was previously considered acceptable. In the 1960s and early 70s production engines often had sodium cooled valve stems. These days it's rarely neccesary.

One thing that was understood years ago was the mechanics of small valve clearances: It wasn't until that 1930s that the idea of engineering a clearance ramp into the cam profile had been thought of. Up until that point valve clearances of .002 - .003 hot were very common in an attempt to reduce the clatter. Despite that tiny static clearance the engines worked without sacrificing the valve seats - mainly due to the limitied expansion of a cast iron block bolted to an aluminium crankcase.

Bearing in mind the age of the internal combustion engine, many of the points raised in this thread hadn't even been thought of until relatively recently