burning smell after gearbox work

[skullcandy]

Hi All and Happy Christmas!

As the proud new owner of Brummies 3.6 into SC, I have been busy getting a few jobs done on the car since purchase. Apologies that this is one of my first posts since then. I live in Herts, just outside Watford and hope to attend meets etc in 2019. I dont know if anyone is local to me but I would be up for a drive anytime someone fancies it (provided its dry of course!). This is my first 911, having lusted after one for 20 plus years.

The major job was to open the G50/21 gearbox and resolve a slightly graunchy 5th gear synchro. I could have lived with this as, with a slight pause, 5th went  in ok and of course I had 6th. Brummie had lived with it since day one apparently. However I found it annoying and although i could not really afford it, i decided to get it done in the name of long term ownership pleasure! The car duly went into a IB highly regarded local 911 specialist for the work. Once apart, it was apparently obvious that the specialist Brummie had used to check over the G50 had put it back together slightly incorrectly. Anyway, so the actual job was very simple and only the 5th (and 6th gear as a precaution) synchros were replaced. Whilst the gearbox was out a very heavy clutch pedal was also resolved.

I now have the car back and whilst the whole gearbox is a joy to use, I have noticed a couple of issues, both of which I will mention for completeness:

1) after 15/20 mins of driving spiritedly on the open road, I have noticed that there is quite a noticeable burning smell in the cabin. It made me pull the car over and check for signs of smoke etc but there was nothing. I have driven it 3 times since getting it back and probably done 60 miles in total

2) the usual G50 chatter noise seems to be present more often. Before it was only noticeable when the car was under load, from 2-2.5k revs but now it is also present when lifting off.

I think most IBers with an interest in hot-rods know the car had a 3.6 varioram fitted with the 6 speed euro G50. Brummie had the gearbox shortened, had a bespoke RS flywheel fitted and a new Sachs clutch. Below is a couple of Brummies pics. The car has done 3-4k miles since the car was completed by Brummie so the clutch is still very new.

Before I speak to the specialist who did the work, Id be grateful for some views re what may be going on and is there any reason to worry. Unfortunately I am not very knowledgeable re mechanics. My concern is that if there is an issue then it will be a major undertaking for the specialist to remove the engine and gearbox so not a quick fix and a case of "just pop the car back in sir"

 

Thanks very much for any thoughts.

 

 

 

Thanks

[Northy]

Is the burning smell oil or something else? 

If it takes 20 minutes it sounds like it’s linked to the car getting up to temp. If it’s oil burning it will be getting onto the heat exchangers somewhere. They’re the hottest thing back there.  Have you got the heat on? 

You should be able to get underneath and see pretty easily.  Grab a torch and have a look underneath. 

[skullcandy]

Thanks very much Northy, I will have a look underneath the car. I dont think I had the heat on but cant be sure. I would describe the smell as quite acrid but Im not sure what burning oil smells like exactly. There was certainly no oil drips on the floor under the car when I last checked. I will get the torch out and have a proper crawl under the car.

[Northy]

I’m no expert but I would have thought if it’s electrical you’d smell it all the time, but that’s pretty acrid. 

Clutch and brakes: you probably know what that smells like. 

Fuel: I think you’d smell the fuel rather than smouldering. 

[Beaky]

As Northy says, sounds like oil burning on a hot surface, I think an electrical fault would also have some smoke.

If not heat on, did you have the front fan on to demist the windscreen, if so then smell maybe emanating form the front blower.

If possible drive for 20 minutes, get the smell back then quickly use someone ramp to get underneath and locate the smell.

Good luck 

[skullcandy]

Ok thanks guys, I will try and find a friendly garage or simply drop it back into the garage that did the work. My main concern was that it was clutch related but I am reassured that no one has mentioned that

[Northy]

5 minutes ago, skullcandy said:

Ok thanks guys, I will try and find a friendly garage or simply drop it back into the garage that did the work. My main concern was that it was clutch related but I am reassured that no one has mentioned that

Clutch has a very distinct smell, I would think you’d know if it’s that. 

[skullcandy]

I dont think I've ever smelt a burning clutch Northy, can you describe it?

[Busybee]

Sounds knackered. Give you 5k for it 😂

Seriously though, are you moving when you smell it? Unlikely to be oil as that’s all behind you and if you’re moving, you won’t smell it till you’re sat still? I’d have a look at electrics. Something is heating up. Maybe behind the dash? 

Oh and acrid smell - wire insulation! Caution dude. 

[Beaky]

50 minutes ago, skullcandy said:

I dont think I've ever smelt a burning clutch Northy, can you describe it?

High rev, slip the clutch, you'll soon smell it 

[Nige]

Check you're getting nothing more than 14.4v at the battery whilst the engine is running.  Anymore and it could be over charging the battery, which then gives off acid fumes.  Maybe the regulator has been disturbed with the work you have had done?

[Northy]

If oil is dripping onto heat exchangers you probably will smell it on the move. The rear blower or fan (depending on backdated heating or not) will blow the hot air to the cabin and bring some burning oil smell with it. 

I can’t really describe clutch smell - almost sweet? Maybe. You could try letting it idle up to temp to see if it’s clutch related.  

Obviously if it’s electrics, you need to be careful (Nige’s is a good shout).

I think you need to try and locate the smell first. That will help. 

[Jonny Hart]

Smell guide:

Clutch.  Nutty.  Flapjacks left in the oven. 

Oil.  Sickly, choking and makes your eyes sting.  Fire in a diner.

Electrical.  A bit fishy.  Nylon socks on a fan heater.  

Rubber.  Pikey bonfire. 

[skullcandy]

2 minutes ago, Jonny Hart said:

Smell guide:

Clutch.  Nutty.  Flapjacks left in the oven. 

Oil.  Sickly, choking and makes your eyes sting.  Fire in a diner.

Electrical.  A bit fishy.  Nylon socks on a fan heater.  

Rubber.  Pikey bonfire. 

Brilliant

 

Thanks for the other pointers chaps

Edited December 23, 2018 by skullcandy

[mean in green]

I think the likeliest thing is dripped / leaked oil burning off the exchangers.

Go for a decent drive with the heat off to burn residual oil off.

Clutch issue - possible, but seems unlikely.

[Nick93]

May be wide of the mark but it might be worth checking the 'box has been correctly refilled with oil.

[SilverWT]

In my experience, it is normal to get a burning smell the first time the car gets hot after major work. Any combination of residual penetrating oil, sealant, lubricant, degreasers, disturbed dust/crud, and etc., can give this.

As long as it does not persist on subsequent drives there is nothing to worry about.

Mark

[skullcandy]

Thanks guys, managed a bit of a blast this afternoon and didn't get the smell. Hopefully it was just as Mark described.

[Busybee]

Good result. I’ll stand down from “harbinger of doom” mode. What she go like? 

[skullcandy]

Its a great little car. I find the handling of it the most entertaining and surprising thing as it hangs on really well and i find it nicely pointy on the front end . I was expecting it to feel like quite an old car but it really doesn't. Its very chuckable and fun to drive fast. Having said that, Im still trying to give it lots of respect as Im conscious that things could very quickly go very wrong if my ambition outweighs my talent.

The engine is glorious (although having failed to find the funds to buy my first choice car: a 89 with a Redtek 3.8, I would like another 30-50hp! Sorry, how greedy is that!). I love the noise the 3.6 makes: between 3-6k revs it makes a delicious yowl. The 6 speed gearbox is a thing of mechanical precisioned beauty and the 964 brakes with turbo discs and turbo master cylinder are really feelsome and very powerful. So overall Im very happy, although the purchase was bank account busting decision which has left me pretty skint!

Things I need to sort out:

1) I cannot see the bloody dials at all (Ive fitted a lovely little Prototipo wheel). The car currently has 993 sports seats and I plan to change these out for something lighter. Im hoping that new lightweight seats will enable me to sit much lower in the car and resolve this problem.

2)There is a vibration through the steering wheel at 90mph plus. I dont get it at any lower speeds. Any ideas re this? 

 

 

[Dr Rock]

2) Tyres-wheels-suspension are places to look for starters.

Glad you are liking the car!

[Northy]

Sounds like a lot of fun! 

Some fixed back Recaro’s will get you lower in the car. You could rotate your dials yo get a better view of the license losing speeds. You can get them refaced to match the rotation as well. 

Has the 3.6 been mapped by Wayne? If not you might have quite a bit of power still available. 3.6s often make over 300+ bhp. 

 

 

[Busybee]

Sounds awesome. And sounds like you’re really enjoying. Not sure if Brummie did any engine tweaking so you might have a whole pile of hp untapped. These guys will help you prise it out. I’m a bit jealous! Lol vibration at a specific speed has to be running gear related right. Get the wheels rebalanced first? 

[skullcandy]

Brummie had the car mapped by Wayne and with its free flowing exhaust, it made 317hp. However did Wayne use to use 9M's dyno and was that rather optimistic? Im no expert but it does not feel like 317 hp

The car is also no stripped out lightweight- it was measured at Centre of Gravity at 1300 kilos fully wet. I assume some of that weight comes from the G50 6 speed box but I would love to lose a 100 kilos from it.

 

 

[skullcandy]

14 minutes ago, Busybee said:

Sounds awesome. And sounds like you’re really enjoying. Not sure if Brummie did any engine tweaking so you might have a whole pile of hp untapped. These guys will help you prise it out. I’m a bit jealous! Lol vibration at a specific speed has to be running gear related right. Get the wheels rebalanced first? 

Yes, I was going to get the wheels re-balanced. Would you get all 4 done or just the front 2?