Ready for Painting

Took the car to AK Bodycraft in Isleham near Ely this morning and proceeded to undo all the work we have done. Most difficult thing to remove was probably the exhaust. I put a couple of self tapping grub screws in where the collector slips onto the headers and the head of one of them sheared off which required drilling out. Not looking forwards to putting them back on again.

They kept the dash as I want one of the dash mounting lugs moving slightly and the open edges of the dash glassing and tidying up. They also kept the windscreen to help with moving the holes for the windscreen legs so the gaps don't have to be full of sealant.

Clonking rear end - resolved

In all the engine excitement I had forgotten that I have actually resolved one of the many issues since the car has been on the road.

The clonking rear end when coming on/off the throttle, and clunking when reversing. I thought I had narrowed it down to CV joints but while I was under the car doing something else I thought after almost 1000 miles its probably a good idea to do a general spanner check. The suspension has been adjusted a few times so I went round everything I could see to make sure it hadn't come loose.

It turns out a few things were surprisingly loose. Bellhousing bolts for one, on the passenger side. One of them was only hand tight!

Then the big one - Diff carrier mounts. Took a FULL turn of a socket. They weren't loose, they just weren't effin' tight, which I believe is the precise torque rating required. Since nipping these up there have been NO clonks whatsoever when sharply  transitioning on/off the throttle.

A recurring theme is that every fixing which has needed nipping up has had a plain nut and spring washers. I am now of the opinion that spring washers are useless for anti-shake. One job for the future is to go round and replace any plain nut/spring washer combos for nylocs (unless its somewhere toasty hot of course). Some places like the bellhousing are a bolt into a threaded hole so there I'll leave the washers in (for clearance as otherwise I'll need shorter bolts) but will apply some loctite to the threads.

Engine scare - seems to be ok

The gunge in the header tank caused much worry and headache but appears (not 100% convinced yet) to be resolved. We drained the coolant and flushed it through with the garden hose pipe. We thoroughly flushed the block, heater matrix circuit and the radiator. I started asking questions and reading as much as I could about what brown gunge could be a symptom of - I already knew of course, oil in coolant from a blown head gasket. This tallied up with the car getting quite hot on the rolling road so I feared the worst.

Thanks to some excellent guidance from the cobra forum I tried to remain calm and worked methodically.

Checked oil on the dipstick - appeared normal.
Drained oil and inspected it - normal, no emulsified oil (mayonnaise)
Rocker covers are baffled so no mayonnaise there.
Removed all spark plugs. The rear two on the drivers side are a pig to get out as the engine is actually offset slightly so there's barely enough clearance to get the plugs out. For interest, this is what the plugs looked like:

They look a bit white which would suggest its running lean but from what I gather with modern fuels you can't really read spark plugs any more. Either way what it does confirm is that if I'm to make more progress with the carb tuning I desperately need to get my AF meter installed! Anyway, on with the diagnosis:

No coolant poured out of any cylinders (good!)
Plugs were dry, if a little oily.
Compression test - bought a compression tester but stupidly bought one with a very long body so couldn't get it in the aforementioned rear two cylinders so I couldn't check all the cylinders. The cylinders I did check all read 170psi which is absolutely normal.
The important test - coolant sniffer test. Borrowed a kit from a local garage. I had never used one before, you take the cap off the header tank and shove this chemical tester in. If combustion gases are present (i.e. leaking head gasket) the fluid turns yellow. If not it stays blue.
Test fluid stayed blue.

Feeling brave, we put the engine back together, fresh fluids and went for a short 20 mile drive. The hot running problems in traffic still persist but generally everything was fine. Checked coolant again afterwards, no brown sludge.

The next day, feeling very very brave we drove 90 miles each way to Warwick. Gave it plenty of stick, various conditions. Long periods at very light throttle cruise. Some sharp bursts of hard acceleration, some more prolonged stints at higher revs. Got there and back with no issues apart from the expected - hot in traffic.

Following advice, I've now got the header tank filled far less as it was consistently pissing out the overflow but I just kept on topping it up without thinking. the level is now about 1/3 in the header tank. I had been obsessed with getting the header tank as high as possible so that halfway up the tank equates to the highest point in the coolant circuit (thermostat + top hose bend) but of course that's where my air bleed to the header is, and the system is pressurised during operation as the coolant expands, so it doesn't matter. As an engineer I'm ashamed I didn't realise this and needed it pointing out to me.

Anyway, it seems to be quite happy but I can't help be a little suspicious. All of this meant we had to cancel the paint job but we are now back on for painting next weekend.

Hmm

Hmm well this doesn't look good. The water pump was leaking yet again so no I'm well versed in removal and refitting I drained the cooling system and just happened to glance into the header tank and its all full of brown sludge:

Here's the dregs of what I drained out

This is the offending sludge scraped out the inside of the header tank:

Return to the Rolling Road

We went back for another rolling road session yesterday morning to verify there's no detonation now the timing is correct and also to check the idle circuit is set up properly and see what its like on light cruise/part throttle and do a power run too.

We managed to achieve all this, which was nice. For some reason we couldn't get a reliable lambda value, it kept waving around between 0.8 and 1.0 throughout the rev/load range and at idle it was as high as 2.0 but again varied a lot so we didn't trust it, at idle this variation was probably because of the cam. CORRECTION on this - the cam plays a part but its also because the exhausts are such large diameter using a gas analyser probe shoved up the end of the exhaust the air in the room can get in at low rpm's and muck with the oxygen reading. I have a plan afoot to fit wideband O2 sensors in the collectors, connected to a suitable gauage/datalogger. I'm in the early stages of research at the moment but the Innovate LC1 and AEM 30-4900 systems look pretty good.

We did get stable CO for the 70mph load (to test throttle range) and full throttle power run and it was hovering around 2.5-3.0% which is tad on the rich side at around 13:1 A/F ratio which in my limited understanding is acceptable for these engines.

For the power run we had difficulty stopping the wheels spinning on the rollers, we had to spray WD40 on the tyres to soften them up and strapped the car down to get some load on the tyres. Here is Naomi being used as ballast:

Eventually we got a good power run in and this was the satisfying result:

376bhp and 392ft.lbs torque aren't bad, considering the engine spec I bought was 375/375! That would also explain why my neck hurts after a few good 2nd and 3rd gear blasts! Very satisfying to see the engine is making what it should but there is still the little niggle at light throttle it doesnt run as well as other people with similar engines/hot cams say their engines run (unless they're telling porky pies of course). Another visit might be on the cards at some point but now the focus moves towards prep for painting next week.

The cobra made a new friend at the garage where the rolling road is, a very nice looking GT40 (kit)