Working Out The Tapping On The Top End

[Maccer 0]

I'm trying to find out a cause for my (sometimes) tappy top end. It's not noisy when first started and does not tap audibly if you are driving round town at 1-4k through the gears and doing low speeds. After doing sustained med-high revs like motorway driving, when you pull up at a junction you can hear the tapping is really quite loud, then after a few miles back at lower speeds it all quietens back down again. Oil pressure as per the dash guage appears fine when driving.

 

I'm doing some work to the car currently, I have had the sump off to replace the gasket as it was leaking a bit and I have also:

 

Taken the oil pump off and cleaned the strainer (which only had one little bit of sh1te in it.) Replaced the pressure relief spring and plunger as a precaution. The two springs appeared identical and only thing I noted here was that the sealing ends of the plungers were different. The old plunger had a wide sealing end (only about 0.75mm smaller diameter than the barrel) and a very short, square step down to the rest of the barrel. The new plunger had a longer smooth taper on the sealing end and a far smaller sealing end - a good ~2mm diameter difference between the end and the rest of the barrel. I fitted the new one as on inspection of the oil pump body it appeared to have a tapered rather than stepped internal mating surface - so hopefully it will be a better seal.

 

I've taken the spray bar off the head and cleaned it (although it again looked fine) and sprayed solvent down any channels I could see. I checked the valve clearances while the rocker was off and all were within the tolerances specified in the Haynes. On the cylinder nearest the gearbox both clearances were on the close side - 0.35mm on the exhaust and about 0.17mm on the inlet whereas the rest were more central in the allowable ranges.

 

Other than oil pressure/oil starvation and valve clearances I can only think it could be a semi-sticky lifter? Anything else I should check?

[S@m 156]

I may not be able to help, but the first question everyone will ask is; Which engine?

 

Sam

[Maccer 0]

Ah yes, sorry! A '88 1.6

[Tom Fenton 1,542]

The 8v engine has mechanical lifters, not hydraulic, so oil pressure and a "sticky lifter" do not really apply.

 

Are you sure it is not the beginning of a cracked exhaust manifold that manifests itself when it gets very hot (e.g. after motorway drive).

[Maccer 0]

Could be, I'd ruled it out initially because I had the exhaust manifold gaskets done about 18 months ago, at which point I was told the manifold was fine and the car has always done this ever since I've owned it (~4 years) with no noticeable worsening.

 

Thinking about it you're right about heat being a factor, because after a really long drive it will take a bit longer to calm down than after a shorter one. I suppose it's possible that there's a hairline crack somehwere that is easy enough to miss when cold but could be opening up at temperature.

 

Coincidentally the flex gasket between the manifold and downpipe has just started to creak and graon now so I'll have a proper look at the manifold when I do that.

[petert 586]

The std. exhaust clearance is very wide, meaning noisey. Set exhaust to 0.012" and inlet to 0.010" max. and you'll have a more pleasant engine.

[Tom Fenton 1,542]

Have a careful look at the manifold from both above and below.

The picture below is from a 1.9 that belongs to a customer of mine. You can see a crack is forming by the black line of soot. At the moment (well, the last time I saw the car) this was not yet bad enough to be too loud, but it can only really get worse, so a replacement manifold is sat ready for when the time comes.

[Maccer 0]

I got under there last night and had a look at the underneath of the manifold;

 

 

Can't see any sooty marks from there, will get the airbox off and get a good look at the top..

[ALEX 98 1 Cars]

You could check the cam lobes, make sure one isn't worn. (it should be obvious by comparing them to each other)

Also It could be a worn vave guide, but it's a head off to check really.

[Maccer 0]

The cam looks in really good nick, the engine itself has only done 78k. I didn't take any photos when I had the rocker off but I checked all the clearances and there was no obvious wear on any lobes or buckets.

When I got the car I had the valve stem seals done as it was burning oil. The guy I asked did it for cheap with the head still on by dropping the valves onto the top of each piston to replace the seal, so consequently I don't know if he would have been able to tell the condition of the guides using this method? I'm assuming not? It stopped burning oil so I didn't think any further about it. I'm hoping head-off will be a last resort I don't have to come to!

[Maccer 0]

Was finishing off some other work today and got round to looking at the top of the manifold;

 

 

Oh dear...

 

 

Looks like it's cracked after all!