Head off

[Robbie693]

Thanks Bruce,

I asked because I have seen it mentioned a few times that the carbon ring you leave on the piston crown is to help as a seal..?

I suppose this is not applicable to my situation as the carbon deposits are not complete?

Once I had got the Y-piece off, which was a stuggle because of the amount of firegum on there, the manifold came off easily. This may be because I have a Spyder chassis - I think there is a bit more room.

Cheers

Robbie

[Robbie693]

Another question

Is it ok to de-coke the combustion chambers without removing the valves?

I have been using cellulose thinners but may try redex.

I was wondering if, when using a solvent to soften the carbon, any solvent could get behind the valves and act on the carbon on the back of the valve?

[RotoFlexible]

Is it ok to de-coke the combustion chambers without removing the valves?

I don't recall the history of the engine, but might it not be worthwhile to do a valve job as long as the head is off? I know that a great deal of money can be spent "as long as the head is off" but a valve job is relatively inexpensive and straightforward and is good bang for the buck/pound/euro. It's when you start replacing valve guides and/or seats, doing multi-angle grinds, porting etc. that the cost piles up and the returns begin to diminish.

[Robbie693]

Hi Andrew,

The engine has done minimal milage since it was rebuilt - the piston crowns are still clean around the edges so not much carbon build up.

I don't have valve spring compressors or indeed the confidence to do a valve grind

I was worried that anything I put on the combustion chambers may leak behind the valve and loosen the carbon there? - I don't even know if that would be bad but thought I should be cautious anyway..

[Bruce Crowthorne]

I must admit I have never had much luck using Redex, but I find cellulose thinners works a treat.
Don't woory about it getting behind the valves and doing any harm - it won't!
However, a good trick is to position the head upside down and fill the combustion chambers with thinners. If any gets past the valves (look in the ports to check) then your valves NEED to be reground.....

[Robbie693]

Thanks Bruce, that's good to know

[billwill]

hold up there ----do a leak down test first -----then if it fails then remove the head ---ed

Can you describe this leak down test, please.

I've just changed my head gasket, but I think I may still have a water leak problem.

[robcall]

http://www.wcengineering.com/articles/leakdown.html

gives a basic description

[twincamman]

welll it should be called a leakage test ----screw a into the plug hole --add 20 or 30 pounds of pressure and read the gauge as the air escapes --from the carbs or exhaust or head gasket and at what rate ---you need a tester with a pressure gauge ----ed ---

[twincamman]

welll it should be called a leakage test ----screw a fitting into the plug hole at tdc --add 20 or 30 pounds of pressure and read the gauge as the air escapes --from the carbs or exhaust or head gasket and at what rate ---you need a tester with a pressure gauge ----ed ---

[mikealdren]

Ed,
If you find a post you have submitted has an error, you can edit it later rather than sending another post - I make quite a lot of errors (especially typing) so I'm an expert!

Mike

[billwill]

http://www.wcengineering.com/articles/leakdown.html

gives a basic description

Interesting..

I think I might be able to rig some pressure guages one of those cheap 12v tyre compressors and and my old scuba gear tank to do such a test.

Only bit I don't have is an actual spark plug pressure adaptor. But I saw a Compression tester guage in a local motor bits shop last week at around ?25 so I might invest in one of those.

If only my old lathe was still working, I could make the adaptor. (Its motor has come off its mounts.)

[twincamman]

make one from a n old sparkplug

[rjaxe]

This may be worth considering - compression tester kit which has all manner of adaptors from SCREWFIX for ?16.49 delivery is about ?5 if you need it sent.
I dont have any connection with them.

[twincamman]

2 separate functions --one measures compression one measures leakage ----I dont need a gauge on the leak down tool ---just listen ---if the leak is from another plug hole the good chance the head gasket is leaking --from the exhaust pipe the exhaust valve leak or from the carb an intake valve is leaking ---- -ed