Deformed exhaust valve seats Coupé Fiat 16v Turbo

Competition engines and 'live' projects only. Good photos to illustrate your post are expected.
Wilko
Posts: 11
Joined: July 19th, 2011, 7:08 pm

Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Wilko »

Hello Guy,

Lately we disassembled the cylinder head of my Fiat Coupe 16v Turbo because we had examined the exhaust valves were leaking. The valves are leaking because the surface of the valve seats is so uneven that the valves only touch at two small areas. On the photo's below you can see the exhaust valve seats. We grinded-in the valves very little to see where the valves are touching the seats and where they don't. We examined the following:

- The valves only touch the seats at two areas over a very small portion of the circumference (the red marked sections on the second photo don't touch the valve)
- On every valve seat the two "touching points" lie in a straight line from the spark plug. (blue marked lines on the photo)
- The phenomenon is worst on the inner two cylinders; at the outer cylinders only one seat is leaking.
- No damage is seen at the valves; the valves seem perfectly even along the circumference.
Damaged exhaust valve seats Coupe Fiat 16v Turbo
Damaged exhaust valve seats Coupe Fiat 16v Turbo
Coupe_klepzitt4.jpg (140.65 KiB) Viewed 11108 times
Red marked zones don't touch valves, small portions along blue marked lines still touch.
Red marked zones don't touch valves, small portions along blue marked lines still touch.
Coupe_klepzitt4a.jpg (169.34 KiB) Viewed 11108 times
I want to replace the valve seats but before I do that I would be happy to be sure this problem won't happen again because I already had the same problem one time before.

Have you seen this strange damage to the exhaust valves before? Or do you have an idea what may have caused this damage?

The car is completely original, no modifications whatsoever.
Some history about the car:

Coupé Fiat 16v Turbo, produced October 1994.
Current mileage: 200.000 km
Somewhere around 110.000 km we examined leaking exhaust valves for the first time. We had the exhaust valve seats machined and fitted a new set of valves, which solved the problem for a while.

Thanks in advance for your help,
Best regards,
Wilko van den Berg
Elst, The Netherlands
Nobby
Posts: 87
Joined: August 24th, 2010, 11:58 am
Contact:

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Nobby »

Could it be valve seat recession?
Chris Burgess
GC 01
Wilko
Posts: 11
Joined: July 19th, 2011, 7:08 pm

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Wilko »

Hello Nobby,

Thanks for your reply.
In cases of recession the wear is caused bij the hammering of the valves on the seats, right?
There is defenitely a lot of wear at the valve seats, but the strange thing is that the places with most wear are no longer touched by the valves.
Maybe they do touch in hot conditions?

Regards,
Wilko
Guy Croft
Site Admin
Posts: 5039
Joined: June 18th, 2006, 9:31 am
Location: Bedford, UK
Contact:

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Guy Croft »

Sorry for my tardy reply.

1. A bent valve will leave the witness from lapping all the way round the insert contact face but the witness on the valve will only appear certain regions.
2. A disorted seat insert with contact face out-of-true will give a lapped witness all the way round the valve but the witness on the insert will only appear in certain regions.

I think I got that right!

So you have case (2), yes?

Distortion of the seat inserts on a standard engine can be caused by local overheating, the most likely culprit here being worn bores and rings leading to a high level of carbon contamination on the valve-seat combo. There are other causes esp if the engine is in-any-way modified but that is likely what has happened here.

The carbon interferes with the seal betw valve and seat allowing burning gas to go past the ex valves long before the ex valve opens under the influence of the camshaft. The ex seat inserts distort as a consequence of repeated exposure to the high temperature.

I have seen exactly the same happen due to detonation, albeit on a non-standard engine.

That is my first thought, I may be wrong. Feel free to respond.


G
Guy Croft, owner
Wilko
Posts: 11
Joined: July 19th, 2011, 7:08 pm

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Wilko »

Hello Guy,
Thanks for the response.

Indeed number 2 is the case, the valves are, at least for the eye, straight and even.

About the carbon contamination being the cause of the valve seat distortion: There are some pro's and con's about this theory:
Pro:
- Lot of carbon in the combustion chamber and on the piston. (is this a lot? I don't see a lot of engines taken apart)
Con:
- Valve seats were completely clean when we disassembled the head (otherwise, this maybe because some oil seeped along the valve guides as the engine didn't run for years)
- Cylinder walls look in very good condition and the engine didn't use much oil nor produce a lot of smoke.

About detonation:
- Would it be possible that this damage occurred due to a defect knock sensor?

Thanks for thinking with us.
Best regards, Wilko
Guy Croft
Site Admin
Posts: 5039
Joined: June 18th, 2006, 9:31 am
Location: Bedford, UK
Contact:

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Guy Croft »

Good reply.

if it's 'det' you won't know for sure until all the carbon is cleaned off the head by means of a gentle solvent like Gunk and hot water. Use of abrasive may destroy the evidence. You will see tiny pin-inappropriate holes all over the inlet side squish band (where the detonation always propagates from..)

G
Guy Croft, owner
Wilko
Posts: 11
Joined: July 19th, 2011, 7:08 pm

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Wilko »

Okay thanks for the quick reply.
We'll take a closer look at the head if we can find any other signs of detonation.

Regards, Wilko
Brit01
Posts: 825
Joined: June 28th, 2011, 4:54 pm
Location: Uruguay

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Brit01 »

Not sure if this helps.
When I did my first rebuild this is what I found on one cylinder (infamous for problems on chamber #3).

You can see pitting. Also it was evident on the corresponding piston. But these Alfa boxer engines luckily have very hard seats and valves. Really robust and can take a lot of abuse. This example is 25 years old. You can see some of the area has been eaten away by detonation around the valve and spark plug.
They have 175-180+ psi compression per cylinder.
Attachments
detonation.JPG
detonation.JPG (116.76 KiB) Viewed 10966 times
Wilko
Posts: 11
Joined: July 19th, 2011, 7:08 pm

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Wilko »

Thanks, I'll see if I can find anything like this.
W
Wilko
Posts: 11
Joined: July 19th, 2011, 7:08 pm

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Wilko »

Hello again,

My dad cleaned up one combustion chamber, see pictures below.
Inlet valves
Inlet valves
Coupe_klepzitt5.jpg (113.18 KiB) Viewed 10921 times
Inlet valve seats
Inlet valve seats
Coupe_klepzitt7.jpg (106.08 KiB) Viewed 10921 times
Close-up between inlet valves
Close-up between inlet valves
Coupe_klepzitt9.jpg (88.85 KiB) Viewed 10921 times
Exhaust valve seats
Exhaust valve seats
Coupe_klepzitt6.jpg (103.17 KiB) Viewed 10921 times
Close-up between exhaust valves
Close-up between exhaust valves
Coupe_klepzitt8.jpg (92.17 KiB) Viewed 10921 times
The surface look to me to be normal casting roughness, but I may be wrong.


A different question: I have two spare 16v heads:
- one Tipo 16v series 1
- one that was said to be from a coupe 16v Turbo but I don't think that's ture, casting year is '90.

Would it be possible to use one of these heads to replace the head of my coupé 16v Turbo even it is a non-turbo head?
Or in other words: are all Fiat/Lancia 16v heads the same or are there differences in strength, machining etc.
The main casting number of all heads is the same: 7669070
I know there are differences in valves, camshafts, etc, but I would like to know if there are differences between the bare heads.

Regards,
Wilko
Guy Croft
Site Admin
Posts: 5039
Joined: June 18th, 2006, 9:31 am
Location: Bedford, UK
Contact:

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Guy Croft »

it's normal not det.

Get the head to GC for repair.

GC
Guy Croft, owner
Wilko
Posts: 11
Joined: July 19th, 2011, 7:08 pm

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Wilko »

Hello Guy,

Thanks for the quick response and the offer to fix the head.
However I already got the head to the workshop here in the Netherlands (but no work is done to it yet).
I don't know what to do because I'm still not sure about the cause of the problem.
If the fit or the material of the seats is the cause, replacing them will solve the problem, but otherwise it is likely to happen again.
Therefore I am asking around if anyone has seen this phenomenon before.

You offered to fix the head, what kind of repair would you propose?
And are you sure that this will solve the problem?

Thanks again for the help
Best regards,
Wilko
Guy Croft
Site Admin
Posts: 5039
Joined: June 18th, 2006, 9:31 am
Location: Bedford, UK
Contact:

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Guy Croft »

Whatever the problem is it is not caused by the head per-se!


G
Guy Croft, owner
Wilko
Posts: 11
Joined: July 19th, 2011, 7:08 pm

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by Wilko »

That's true for sure.
I'll see if I can find another culprit.

Wilko
tmvolumex
Posts: 165
Joined: July 7th, 2006, 12:43 am
Location: USA
Contact:

Re: Deformed exhaust valve seats Coupé Fiat 16v Turbo

Post by tmvolumex »

its sounds like 100,000 km is the time for a valve job on ht engine. Guy should know what is typical for a Fiat 6 valve turbo, I dont.

You wrote:

"Somewhere around 110.000 km we examined leaking exhaust valves for the first time. We had the exhaust valve seats machined and fitted a new set of valves, which solved the problem for a while."

You are now at 200,000 km IE you put on another 100,000 km since your last valve job.

Another possibility is the head was not surfaced correctly, rendering it not flat which can also warp the valve seats upon installation and torquing down.
Another possibility is that the block deck is not flat. If the deck is not flat it will warp every head you install on it. Overheating the engine can do this.
Check the block for flatness before installing another refurbished head.

I would also check the quality of the replacement valves installed at the head rework.

Tom
GC_31
Post Reply

Who is online

Users browsing this forum: No registered users and 50 guests