Oh cock! Melted a plug!

supercharged spaniel · December 30, 2008, 12:47:36 PM

i doubt you will get the clutch in without taking the box out as there is very little room. worth a try but i very much doubt it...wtf about the water pump though?! thats seriously not good! obviously been given the wrong year waterpump of the two available and just made do or not even noticed! that alone is worth noticing whilst in bits.

lance · December 30, 2008, 01:13:30 PM

before anything id be getting them injectors tested mate!

Robin · December 30, 2008, 01:43:04 PM

injectors have been tested then cleaned and then tested again, all matched pretty much spot on.

lance · December 31, 2008, 02:15:45 PM

looks like its ran lean mate, fuel pumps good?

Robin · December 31, 2008, 02:22:09 PM

no problems with the fuel pumps as i run a wide band AFR meter in the car and that was reading 0.78 lambda.

I'll check the fuel rail before i out it back on.

Dan · January 02, 2009, 12:52:18 PM

Pretty bad the spark plug melting like that. Were they genuine VW W5DPO's or ones from GSF ? Would be an even more expensive problem if it had happened to a new BVH. I'm sure those of us getting them done will share a big concern of this happening again !

hayesey · January 02, 2009, 02:01:49 PM

ones from GSF are proper Bosch ones though I'd expect them to be good quality. I'd put it down to a freak manufacturing defect or that cylinder running lean for some reason.

PeteG40 · January 02, 2009, 05:00:01 PM

well cylinder one gets most heat from the least efficient exhaust port - so maybe it overheated that cylinder - what with the shit water pump

Dan · January 02, 2009, 07:28:26 PM

The plugs bosch make for VW may be to a slightly better standard than std aftermarket ones with their name on. As they are roughly the same price I know where I will be getting a set from.

Pete, why has No. 1 got the least efficienct exhaust port ?

PeteG40 · January 02, 2009, 07:56:14 PM

cos its most restrictive due to the bend round the charger

Robin · January 02, 2009, 07:57:24 PM

because the charger is in the way so the pipe has to bend around it and also the charger restricts cool airflow to the cylinder head as well

breadman · January 02, 2009, 09:38:09 PM

The exhaust ports are all the same efficiency wise.
The No.1 exhaust manifold branch does have a slightly tighter turn, however whether the efficiency losses are more than fractional I very much doubt. Even if the manifold was very poorly designed, the significance of the restriction wouldn't be enough to increase combustion temperatures to melt a plug.
There is very little in the way of cooling airflow to the engine anyway, putting the charger in front of cylinder No1. ain't gonna make much difference.
I bet if you could put a temperature probe into each of a G40's standard cast manifold primary pipes, the EGT's in all four would be very similar indeed.
This is either a plug related failure or for some reason the engine momentarily ran very lean on No1 cylinder.

poloeatonm45 · January 02, 2009, 11:22:41 PM

hi i know this is a bit off topic but im interested to know something. i,ve seen inside quite a few g40 engines now and all of them seem to have the edge of the pistons washed clean {the edge nearest to the front of the engine} why is this? is it oil washing past the piston rings and washing the edge of the piston clean?

Yoof · January 03, 2009, 12:55:51 AM

Quote from: breadman on January 02, 2009, 09:38:09 PM
The exhaust ports are all the same efficiency wise.
The No.1 exhaust manifold branch does have a slightly tighter turn, however whether the efficiency losses are more than fractional I very much doubt. Even if the manifold was very poorly designed, the significance of the restriction wouldn't be enough to increase combustion temperatures to melt a plug.
There is very little in the way of cooling airflow to the engine anyway, putting the charger in front of cylinder No1. ain't gonna make much difference.
I bet if you could put a temperature probe into each of a G40's standard cast manifold primary pipes, the EGT's in all four would be very similar indeed.
This is either a plug related failure or for some reason the engine momentarily ran very lean on No1 cylinder.

I partially agree, but what you say isn't strictly ture.

The exhaust ports themselves are the same efficiency wise, the exhaust manifold itself isn't. The increase in pumping energy required on Cyl. 1 to clear the tight radius will have an effect on EGT after a few cycles. I agree with you about it not being significant enough to melt the plug. The charger brackets etc do make a differance on block distortion, they're basically a heatsink for the exhaust, and as such retain alot of latent heat, don't be so quick to rule things out.

Personally I think it's a bad plug. I've not seen it yet but even with Robin's state of tune (circa 160bhp) a W5DPO should withstand the increase in EGT. Also there would be evidence on other plugs of a failure about to occur if fueling or ignition timing where indeed the case.

The injectors have been flow tested a few times and came out fine, the fuel rail can't really go wrong either, it's a plastic rail! and Cyl. 4 is furthest away from the intake anyway, so I expect this would experience the biggest pressure drop.

I no longer run Bosch plugs, and havn't for a long time as they don't like nitrous and I find when you go boyond the relms of W4 they like to missfire when cold. NGK are far better (and cheaper) one of the few things people pay attention to until they go wrong like this!

poloeatonm45 · January 03, 2009, 07:40:51 AM

what are the codes for the plugs you are using yoof? why are they better? do the cope with the heat better ?

steven