Yamaha TRX850 Enthusiasts Forum

I've been working on the maintenance today and would like to share some thoughts.

The valve seals are planned to be replaced. This is how it looks like now


But when I got the exhaust off (which was very easy, because it's not an original one ), I saw this:

One side is black, as I expected (oil ). But the other side is remarkable clean and a little bit the opposite of the other: white! Was the mixture too lean?
Inside the engine it looks the same. The valve on the right is so white it almost scares me! (The flashlight made it even more extreme though, almost fluorescent)


Well here's another thing. I run Mikuni flatslides, with the original air box. I ordered these funnels - or how do you call them? - "sports kit" from KEDO. I tried one of them on (left side) and it showed to me that other side (mounting on the genuine air filter box) covers these nozzles. I guess this is more racy but what if dirt and sand gets into it? Any ideas about being this a good or a bad thing?


Tomorrow I'll be ready to get the head off. Fortunately I have the luxury of working inside!

The `what do you call them`s` are spun alloy bellmouths.
There`s definately an indication of weak mixture on the left hand cylinder(viewed if sat on the bike)Tarwetijger,although the other side doesn`t look too bad really,a tad rich perhaps,althought the colour on the exposed valve stem isn`t too bad.
Very likely you do have some oil burning issues too,could just be hardened valve seals allowing too much by though.

Steel gauze at the end to keep the moths out!!

Dave E

Mincehead wrote:The `what do you call them`s` are spun alloy bellmouths.
There`s definately an indication of weak mixture on the left hand cylinder(viewed if sat on the bike)Tarwetijger,although the other side doesn`t look too bad really,a tad rich perhaps,althought the colour on the exposed valve stem isn`t too bad.
Very likely you do have some oil burning issues too,could just be hardened valve seals allowing too much by though.

That's it, bellmouths - couldn't remember it.
Well I was thinking about a dynorun when i'm finshed, but now I'm sure.
The oil burning is the reason I'm doing this. I'm replacing the valve stems and I think I will replace the pistons rings too.
Other than that, the bike ran fine though.

slow codger wrote:

Steel gauze at the end to keep the moths out!!

Dave E

Nice, were do I get those?

But here's what I meant

try this place

http://www.brspecialtuning.co.uk/Keihin.htm

Dave E

Progress of today.


The head looks alright, besides some carbon desposit.


I bought a valve compressor especially for this job, but its to big!
So spend the afternoon to make an adapter. (left on the last picture).

Btw, any hints on the best way to remove the carbon?

Tarwetijger wrote:Btw, any hints on the best way to remove the carbon?

Don´t know the english for it but in swedish it´s called "kaustik soda", you can put water with some in it in the exhaust pipes and after a while you dry it with a heatgun and then it´s just to bang on it a bit and it falls off....should work on valves etc. as well.

Killerwhale wrote:Don´t know the english for it but in swedish it´s called "kaustik soda",

It's the same in English, just replace the K's with C's and you get Caustic Soda!

I'll be following this with great interest. I'll be doing the same soon (valve stem seals and rings, also cam chain and tensioner!)

Tarwetijger wrote:Btw, any hints on the best way to remove the carbon?

Get the marigolds(rubber gloves)on Tarwetijger and between caustic soda applications utilise wire wool(coarse first,followed by medium then fine).
You can also use an oven cleaner foam(comes in aerosol form)although don`t do it in a confined space the fumes are nasty.
Then you can `finish` the combustion chamber with fine grade wire wool and T Cut or metal polish.

Killerwhale wrote:

Tarwetijger wrote:Btw, any hints on the best way to remove the carbon?

Don´t know the english for it but in swedish it´s called "kaustik soda", you can put water with some in it in the exhaust pipes and after a while you dry it with a heatgun and then it´s just to bang on it a bit and it falls off....should work on valves etc. as well.

Err, are you sure? From the Wiki link from Redkiwi:

In 1986, an aluminium road tanker in the UK was mistakenly used to transport 25% sodium hydroxide solution[citation needed], causing pressurization of the contents and damage to the tanker. The pressurization was due to the hydrogen gas which is produced in the reaction between sodium hydroxide and aluminium:

2 Al(s) + 6 NaOH(aq) → 3 H2(g) + 2 Na3AlO3(aq)

I don't want extra holes in my head (*)

(*) cilinderhead that is

Hmm... is Kaustik Soda also used as drain cleaner?

Yes, I've soda here (it doesn't say caustic btw), and the package says it can not be used on aluminium.
Or is that just the reason that it works so good?

Yes it does react with aluminium but if you`re using it and watching the effects you`ll be able to guage how it`s doing.
It`s not likely to reap carnage on the combustion chamber all the time you`re monitoring it.
Alternatively you can use a piece of aluminium strip and file an edge onto it,that way you can use it to scrape the carbon deposits off before using the wire wool and polishing agents to get a nice finish.
Don`t forget the abrasiveness of wire wool will work pretty well in removing the carbon build up too.

I'll give it a try. The only thing I still haven't figured out, will the wire wool not damage the valve seats or guides?
Or should the wire wool only be used with the valves in place.