Technical very hot exhaust...

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Technical very hot exhaust...

zp*

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hi,

My 1.6 Tempra SW is on the road again, after lots of work, thanks to your help!
Apart from the fact that 50% of the 86HP seem to be missing (dunno where they might have gone...), i was surprised by a burning smell coming from below the car, after a short (10 minutes) test drive ; and the exhaust is running very hot. The muffler pipe's tip at the rear of the car is so hot you can't touch it.
I don't think this is normal but i don't know what could cause the exhaust to be running hot?
I replaced the timing belt, and made sure timing marks lined up properly. I was surprised that timing mark for the camshaft is on the sliding plastic bit. I suppose you have to adjust timing mark when the sliding bit is entirely raised? If yes then timing is ok.
Apart from misadjusted timing, what may cause exhaust to be running so hot? lean mixture? blocked exhaust? Any help appreciated...

All the best,
zp*
 
maybe the exhaust gasses are making it hot? just a thought... anyway is it a new exhaust. if it is when they're first run in the paint on them or whatever it is makes a burning smell as they are exposed to the heat. if it persists it may be a problem.
 
hi,

the rear exhaust muffler is three years old.
I can see two reasons why the exhaust would get hot :
1) one exhaust valve is sticking or bent and fuel burns in the exhaust pipe instead of combustion chamber...i doubt it but will check compression to be sure
2) the exhaust is clogged somewhere ? A friend of mine told me a clogged exhaust on his motorbike caused the tip of the muffler to get so hot it was glowing red in the dark...but never experienced it personally. il will dismantle it to check if something rattles inside.

Any thoughts appreciated.
Regards,
zp
 
Hi,

I don't think it's running lean...last week the engine would idle nicely, i adjusted idle and mixture, the car was running smoothly.
The next day, the idle is non-existent, engine stalls, no power...
I checked spark plugs, they are a little white which might indicate lean running. I can look for a clogged jet in the carb, which would surprise me since i cleaned it last week...
Do you think lean running could cause the exhaust to get that hot???

regards,
zp
 
pulling the slider up to full up is the correct position when fitting a new cam belt for the top pulley,so this is not the problame,unless it is not on top dead centre {pistons at top} when fitting the belt..................
 
Hi,

Still trying to solve my problem...my tempra works now but still has the following symptoms :
- no idle below 1500 rpm when cold (adjustment with the cold start fast-idle device)
- no idle below 900/1000 rpm when hot, sometimes the engine will stall unexpectedly
- very rough idle, the engine runs unevenly, and misfires are clearly present in exhaust gas flow
- lack of power unless throttle is fully open
- unusually hot muffler tip
The car won't pass technical inspection due to this problem.

Here's what i did so far :
- carb overhaul with brand new gaskets, diaphragms, all adjustments carried out by the book
- replacement of ALL petrol and vacuum hoses, new hose clamps ; vacuum check : i'm sure there's no vacuum leak at intake
- carb swap with a known good unit from a Tipo that has same engine, carb (weber TLDE 23 151), and ignition unit : no improvement
- new marelli F8LCR spark plugs, high voltage leads, rotor, distributor cap
- ignition check with Fiat diagnostic equipment : no fault
- full gas tank from a Shell petrol station
- replaced timing belt & tensioner, checked timing : OK
- checked compression : ok but a little low on two cylinders
- checked valve clearance : exhaust valve clearance too high on the two above mentioned cylinders.......looks like the two valves are slightly bent! the previous owner had experienced a cambelt failure two years ago (the repair invoice says the head has not been off and compression was checked to be ok after new belt was fitted) ; i assume the mechanics did a quick & dirty job and didn't notice the bent valves.
So i'm going to remove the head to carry out valve repairs...
I read in the manual head bolt torquing is 20Nm -> 40Nm -> 90° -> 90° but no mention to a "retorquing" after 1000kms was made. Is such an operation necessary? It would be a real pain since torquing the head without camshaft removal requires a specific wrench to gain access to out-of-reach bolts...

all the best,
zp
 
Looks like valves are your problem Zp.

As for tightening torques, I can only speak as a Tds Diesel owner but the principle should be the same.

As far as I know the head bolts are "pre tensioned" or "stressed", that is once you have them tightened down they do not need to be redone, at least that was the case for the diesel. I would have thought retourquing should not need the camshaft removal, the diesel does not. Fiat head bolts are usually the square form "castellated" sockets, a bit like a "torks" but square not pointed, they are easily obtained from your motor factors or tool supplier.

Remember to replace the seals on ALL the valves not just the bent ones (your head gasket kit should have all the bits required), you will also need to bed in the valves to the old seats.

Does the manual have the tightening order ?, should have, if not do it in a spiral pattern working out from the center bottom, all to 20, all to 40, Etc, sorry if you already know this. You may have a secondary smaller set of head bolts from the main ones, if there are they are usually at a lower setting to the main bolts.

If you can, its better to get new head bolts, old ones are not good for reuse after 2-3 times because of the "pre stressing", I have reused on a Diesel but only once. You should also have the head skimmed, but you may get away with it.

Oh - and keep things nice and clean as you rebuild the engine, wipe of excess oil and dirt, the faces of the head and block must be clean or you may get a leak, new gaskets all round, watch out for stray nuts / bolts / bits dropping into the engine.

My Tds rebuild is still going strong 25,000m later, the last time the garage did it it only went 7,000 - bunch of cowboys.

Good luck.
 
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Hi,

after removing the head...i was right! exhaust valve #4 is bent! (very slightly but it leaks)
still took me two hours to remove the head...

regards,
zp

dscn1361uh5.jpg


dscn1362xj5.jpg
 
Last edited:
Hi,

yes i'm fixing it anyway, hoping it'll run better after a valve job.
i removed the valves yesterday, in fact none of the exhaust valves are seating properly : lots of carbon build-up, pitted seats and valves.
no wonder the exhaust manifold has a bright red coloration on all four ports...
so this means new valves, cleaning the ducts with wire brush, valve lapping.
after this i should have an engine ready for another 150 000 kms!

all the best,
zp
 
Hi,

here a picture of the valves...exhaust valves are badly burnt

52034563.jpg


have checked valve to guide clearance...a little out of spec but nothing alarming...i'm lapping th valves while waiting for the gasket set...

69c6ebee.jpg


regards,
zp
 
The white carbon on the valves would indicate the engine running too lean, possibly with retarded ignition timing. Check your vacuum pipe to the Digiplex and clean the jets in the carburettor. OK, so you have replaced the carburettor and replaced all the pipes... I really don't know what else you can do...

I think, once you've reassembled the engine, you should try to monitor how lean it's running by looking at the spark plugs for signs of overheating, plus the exhaust as you've mentioned. Maybe the leaking exhaust valve caused a 'scavenging' effect that drew fuel/air mixture away from the other cylinders. It's a bit of a long shot, but hard to think what else would cause such lean running.

-Alex
 
Last edited:
Hi,

it's very likely that the engine ran lean in the past. All rubber hose including the vacuum pipe to the digiplex were badly torn. When i was given the car, it hadn't been running for more than two years due to an alternator fault. However, the carb was clogged with debris and everything was in pretty bad shape under the hood. Wrong spark plugs, oil leaks (including an oil leak in the dizzy cap), crud everywhere, you get the picture. Besides the thermostat was stuck open and the engine simply couldn't get hot, which accentuates lean running.
In fact, none of the valves was bent but all of the valves were badly pitted (especially on the exhaust side) and didn't seal properly anyway. I wonder if this is due to the car remainig parked during two years? Anyway, valves are now tight and i'll re-assemble everything next week...i'll keep you informed.

all the best,
zp


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Hi,

the rebuild is going on... i hope to have the car running again this weekend!
f05b2b4b.jpg


all the best,
zp
 
Hi,

Many thanks! You may have noticed i'm currently using my living room as a workshop, so dirtiness is not an option!

all the best,
zp
 
Last edited:
Hi,

My engine has just come to life again...looks like it runs smoother now...will test tomorrow!

All the best,
zp

483faf14.jpg
 
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