decoke an alloy cylinder head?

[Crazymanneil]

Hey all.

In process of rebuilding my engine. I have new gaskets etc for it already but was wondering if you have any advice about cleaning the (alloy) head? I read about using oven cleaners etc but all the oven cleaners i've come across specifically state not to use them on Aluminium? The head and block are in great condition, so should be a matter of cleaning them up and putting it back together.

Neil

[oldbmw]

I would use a brass brush in a drill or grinder.

[Diesel Dave]

Decoking alloy - don't use any oven cleaners as they rely on Caustic Soda as the active ingredient and this will dissolve alloy.

Soak the carbon in oil or Redex for as long as you can.

Use a scrap piece of copper pipe, flatten/open the end and file to a chisel point, make sure the corners are rounded so they don't dig in.

Scrape away carefully.

Have patience, the oil will usually loosen the carbon from the surface so it comes away clean.

[Crazymanneil]

Thanks for the responses guys. I tried some spray oil on it and the carbon seems to be shifting slowly so i'll go this route and put lots of elbow grease in.

neil

[LocomotiveBreath]

What I do, carbon buildup on my Ruggerini/Honda with the high SVO use, causing piston to head contact causing a blown head gasket within the first 6,500 miles. Bouncing the valves off the top of the pistons during my 4,500 rpm trial runs didn't help either. Note, if your going to run a higher RPM, (floating the valves), toss in a little more valve spring pressure.

I use a combination of engine degreaser and fine sand paper and metal polish, being very careful not to remove any material that would cause a lower compression ratio. After cleaning, I eventually polished both the head face and piston crown. I do this to all my engines when I have access to these items. By doing this, to prevent carbon deposits adhering to the polished surfaces verses carbon being able to adhere to the factory machined surfaces.

Piston crowns can be polished with the use of a glass plate with 600-1200 grit paper.

This was done over 14,000 miles ago, and so far so good. Also, no more high SVO use! Bio-diesel is what I use vs. SVO

Good Luck, Dave

[thundercougarfalconbird]

snap-on has a diesel detergent available for a motorvac type system, the fluid is mixed with diesel and sprayed into the intake while running, however i have found it works well soaking parts in it for cleaning

snap-on part # EEFS106AC2

[smokyjoe]

Hi Dave,

Interesting note on the SVO causing excessive carbon. I was thinking of running pre-heated SVO in my bike thinking that the main problem with carbon was "cooler thicker" oil being injected. My engine has the injection pump mounted through the oil cooler, so the fuel gets pretty hot without pre heating. Maybe my thinking about this was flawed. My VW used to run clean on SVO with about exactly the same size cylinder (400cc) and compression ratio but perhaps the air cooled engines run cooler sometimes or have quicker temperature changes hot to cool?

Maybe I should bite the bullet and go the biodiesel route, but it looks like a lot of work and mess to me. Guess I'll never find out unless I try it!

[Crazymanneil]

Yes interesting note on SVO. Were you pre-heating the fuel? I've read that SVO burns without smoke. If its not burning completely then it leaves deposits rather than smoke. Not sure if this is true or not though seems to make some sense. I've been running an IDI engine Fiesta on the stuff for approx 7k miles and an Audi TDI on it too (approx 4k miles) and all ok so far but admitedly early days yet.

Neil

[Darren]

Yes interesting note on SVO. Were you pre-heating the fuel? I've read that SVO burns without smoke. If its not burning completely then it leaves deposits rather than smoke. Not sure if this is true or not though seems to make some sense. I've been running an IDI engine Fiesta on the stuff for approx 7k miles and an Audi TDI on it too (approx 4k miles) and all ok so far but admitedly early days yet.

Neil

Don't think thats true.

I think that with a diesel engine any fuel charge that has not gone through a reasonable combustion event will come out the exhaust as visible smoke.

Excessive unburnt vegetable oil in the engine (due to poor combustion) will cause deposits much quicker than a similar amount of unburnt diesel.

I've seen smoke from poor vegetable oil combustion. Vegetable oil that is poorly combusting has a distinctive smell - kind of sickly sweet, not particularly nice.

Deposits are more likely to form in a cold or cool engine where there is not so much heat available to ensure a good combustion event and, I think I'm right in saying, uncombusted fuel and partially combusted fuel is more likely to settle on cool engine surfaces (after cold starting).

I would regard it as foolhardy to start a direct injection engine on vegetable oil, unless it has been suitably modified (eg. cold starting and cool running aids fitted and/or modified, modifications to injectors). Indirect injection engines are much more forgiving in this respect and tend to have glow plugs which aid initial combustion. Fitting a second fuel tank to allow the engine to be started on diesel fuel is safest.

Vegetable oil combustion tends to be not good on no or low engine load so avoid leaving your engine idling and try and avoid sitting in traffic.

The condition of injectors and good engine compression are more important than when running diesel fuel. Injection pump and valve timing have significant effects on the quality of combustion.

[andrewaust]

I'm wondering if it could be an atomization and/or cylinder head temp issue causing carbon buildup. Air cooled engines can run cold, especially if fan forced cooling is used in cold climates, that's where the liquid cooled engines go well having a thermostat to keep things running relatively warm.

If you think your air cooled engine is running very cold, try gradually closing off the air intake at the fan, but practice caution! Best to do this having a temp gauge on the head somewhere, and if possible one on the oil line as well.



A

[Darren]

Yeah Andrew, I think that the permanent air cooling is definitely disadvantageous when running biofuels.

We've discussed removing the fan for power reasons and adding a temperature controlled electric fan or just doing away with the fan altogether.

Some people have run some stationary engined bikes with fans removed without problems.

I spoke to the fella from Charnwood who developed the Enfield / Hatz IB30 conversion at the bequest of Hatz. He said they found that the engines would overheat in traffic with the fan removed.


Loco Dave,

When you got the coking what fuel mix were you running and I guess you were cold starting on the SVO?

[oldbmw]

on some conversions of diesel to bio fuel they put a steel plate over the top of the pistons in order to keep combustion temperatures up.

[Darren]

Hello Larry,

I'd heard of a French university (Orleans) using this method, some years ago, to improve combustion of sunflower oil. A report used to be available to download from the university website but it disappeared some time ago.

Just found it again at - http://my.voyager.net/~mlh/21Resume1.pdf

As far as I'm aware this is not often done and I cant recall hearing of anyone else using similar methods.

There was an American who was heavily modifying pistons in old stationary engines (Listers or Petters) to induce more swirl and turbulence in the chamber.

Best

Darren

[andrewaust]

Great pdf Darren , it actually answers my theory regarding atomization and combustion temps.

Interesting to see the DI "Direct Injected" engines suffer much more then the IDI "Indirect Injected" engines.

Many put the IDI engines down around the circles I worked with, I've been a supporter of both for specific reasons. IDI engines do not rattle as much or suffer from injector nozzle hole blockage due to the pintle needle protruding from the nozzle, heads can also be lifted off with injectors installed, not a good idea with ID engines as the nozzles nearly always protrude past the head facing, so if dropped face down there goes the injectors.

ID engines also have advantages too, they are slightly more economical due to thermal properties as IDI engines loose some energy from heat transfer to the pre combustion chamber. DI engines are easier to start, many not needing a starting aid such as glow plugs.

Interesting to see the converted DI engine also suffering from a reduced economy due to thermal transfer.

Its all a learning experience



A;)

[Darren]

If you are interested in reading research papers about the use of pure plant oils as a fuel I posted loads more links to study abstracts and full study papers at OBED

in the research section-

http://obed.org.uk/

and in the wiki-

http://wiki.obed.org.uk/index.php?title=Pure_plant_oils