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Re: 1969 Fiat 124 SpiderAS 1800 conversion

Posted: Wed May 24, 2017 9:07 pm
by Guy Croft
Hi Charles - will get on this soon as I can.

very sincerely,


Re: 1969 Fiat 124 SpiderAS 1800 conversion

Posted: Thu May 25, 2017 8:49 pm
by Spider 1969
OK Guy, I know you're even more busy than normal so take your time!

Very sinceerely,


Re: 1969 Fiat 124 SpiderAS 1800 conversion

Posted: Fri May 26, 2017 10:42 am
by Guy Croft
1 The operator did not want to rev the engine above 7500 rpm even though he felt it did not yet run out of breath. What would be a safe rev limit for an 1800?

- if not on race pistons and rods I would cap it at 7800

2 Looking at the AFR graph it is a tiny bit lean above 5500 rpm. Would a smaller air correction jet yield result or is it too close to the optimum power AFR line. (I should have asked the operator yesterday and will do but would like your opinion also)

- yes

good work Charles!


Re: 1969 Fiat 124 SpiderAS 1800 conversion

Posted: Fri May 26, 2017 11:51 am
by Spider 1969
Many Thanks Guy!

very sincerely,


Re: 1969 Fiat 124 SpiderAS 1800 conversion

Posted: Tue Sep 19, 2017 8:52 pm
by Spider 1969
The event:
Last week when accessing the motorway in a u turn and accelerating fast suddenly a knocking sound occurred. I took my foot of the throttle and away it went until accelerating again. Oil pressure remained close to 60PSi so no bearing issue. Coolant temperature was 76 degrees C. I left the motorway on the next exit driving 60 km/h, parked at a fuel station and called a lorry to take the car and me home.

Circumstances prior to the event:

Short recap of the engine spec: 1756 cc TC, CR 10:1, GC modified head, GC2B inlet cam, OE exhaust, GC forged pistons, twin IDF 44, Filter King regulator and fuel filter, sealed cold air box with duct to remote air filter in front of car, 123 electronic ignition, low coolant temperature in head thermostat, aluminium radiator. 157 Bhp@7326rpm, 173Nm@5755rpm.

First start up April 2016, driven 10.000 km since then.

During engine life I have experienced a couple of times that the engine did not run on all cylinders on minimal throttle opening during cruising at low speeds. When opening the throttle (driving faster) it went away. The speed range above which varied from 95 km/h to 120 km/h. I suspected that the progression holes in one ore more carburettor barrels got partial clogged. Usually this phenomenon stopped after a while or after driving very fast or accelerating to 7500 rpm a couple of times. Last two times this occurred I noticed that cylinder 3 and 4 were not contributing on idle as I could pull the plug lead without effect on idle speed. I thought this to be caused by debris in the idle and progression circuit. I have never found debris however in the carburettor fuel bowls and fuel wells so it may also be the carburettor synchronisation off tune.

First 3000 km’s I have driven the engine on a wrong timing curve which had the effect that total ignition advance @ 3500 rpm and above has been 46 degrees where as 36 is considered to be maximum for the TC.

Coolant temperature has been fluctuating fast between 65 degrees C and 86 degrees C depending on ambient temperature, (air)speed and load. Below cruising at 90 km/h it can be 80 degrees C and when I accelerate to 125 km/h air speed to the aluminium radiator increases and it cools fast, depending on ambient temperature, to as low as 65 degrees C sometimes.

Fuel used has always been 102RON octane which is locally available (and methanol free so no issues with perishing tubber materials, no water in fuel etc.)

In the week prior to the event I noticed bubbling in the coolant expansion vessel. There was no oil in the coolant nor sludge in the oil. Compression test did not indicate a leaking head gasket (at that time) as all 4 cylinders gave 170 Psi.

The cause:
Once home I executed a compression test which confirmed my suspicion of a failed head gasket between cylinder 3 and 4 as the pressure in cylinder 1 and 2 was 170 Psi and in 3 and 4 it was 40 Psi. After head removal this was indeed observed. Gasket has not been damaged in other areas. The observation of gas in the coolant expansion vessel probably has been a precursor of the event caused by gas migration through the soft part of the gasket after the fire ring had been initially damaged.
Fortunately gasket faces of the block and head were not warped or locally damaged.

This leaves the question about the underlying cause of the head gasket failure. Possible causes of head gasket failure are:
1. Detonation due to high temperature of air intake and or high coolant temperature: not likely as engine has sealed cold air intake and low temp coolant thermostat.
2. Detonation due to wrong ignition timing. As the engine has seen too much advance in the first 3000 km’s of its life it may be possible that the damage has been initiated at that time. One would expect however that damage is not limited to the gasket part between cylinder 3 and 4. Curve has been set at 34 degrees including 10 degrees static advance.
3. Detonation due to wrong octane fuel: not likely as 102 has been used throughout.
4. Detonation due to over lean fuelling: possible as the engine has not been running on all cylinders during part throttle on a couple of occasions due to fouling and or wrong synchronisation between front and rear carburettors. Rear cylinders have been observed not to contribute on idle; the location of the gasket failure. Plugs and combustion chamber were black and not whitish as expected to be from lean mixture. The black carbon and soot may however be formed after the gasket failure. Action: check synchronisation and adjust if needed after start up.
5. Gasket degradation due to steep coolant temperature transients that have been occurring. Possible but one would expect however that the gasket damage would not be limited to one location. Action: To be further examined and air flow through the radiator to be optimized at lower speeds by adding an engine under tray.
6. Gasket failure due to mechanical parts not fit for purpose or incorrect installation. Not likely as GC race head gasket, GC 12.9 grade race head bolts and washers have been used. Head has been modified and skimmed by GC and a new old stock engine block was used (also checked for flatness prior to use). Installation has been executed according to GC instructions.

I have to conclude that the root cause cannot be solidly confirmed at this point in time. Some preventive measures can and will be taken however. Lesson learned is to consider gas in coolant as a precursor of head gasket failure followed by corrective action before stranding on the side of a road.

Corrective action

Gasket faces on Head and engine block cleaned with solvent and scotch brite. Head bolts have been cleaned as well the female threads in the block. All parts needed have been delivered so the head will be installed next.

Re: 1969 Fiat 124 SpiderAS 1800 conversion

Posted: Mon Sep 25, 2017 8:39 pm
by Spider 1969
Last week I installed the head. Though on the engine stand using guide bolts for the head works quite well it turned out not to be possible in car to use because the head is situated under a beam on the fire wall. For the rest is the installation, commissioning and start up were uneventful operations.

Mismatch in synchronisation was identified to be one of the possible causes but measurements did not reveal an issue. First 20 kms after startup the pick up was not good giving slight misfiring/not running on al cylinders/detonation(?) on progression phase as described before but this vanished and now it is running as before and a joy to drive again. This remains a worrying issue though and I will flush the fuel system once again. Any suggestion from the readers about the origin of or experience with this intermittent problem is highly appreciated.

Re: 1969 Fiat 124 SpiderAS 1800 conversion

Posted: Fri Apr 13, 2018 7:39 pm
by Spider 1969
Update: no work on the Spider this winter as I have been working on a MGB GT inherited from my late father. This has been in a barn for 24 years and I replaced all brakes and overhauled the engine. (No intention of starting up an engine after all these years and the engine strip revealed rust in the bores so once again proof that one should not start up engines after standing idle for long) Engine will be installed and started up within the next week so after that I an start working on the Fiat again as the MGB has been parked under the lift the Spider is on! Bit of a hassle to push the MGB out, I prefer to drive it out ;-)

Today I received a beautiful exhaust header as supplied by a GC agent for the next upgrade on the Spider. Next step is to design and construct a stainless steel 2.25" exhaust system. Looking forward to develop my TIG skills!

Re: 1969 Fiat 124 SpiderAS 1800 conversion

Posted: Tue Apr 17, 2018 12:30 pm
by Will01
What a beautifully looking crafted exhaust!
Good luck with the rebuild

Re: 1969 Fiat 124 SpiderAS 1800 conversion

Posted: Tue Apr 17, 2018 8:00 pm
by Spider 1969
Thanks Will!