how do i check my valve seats are ok?

[super trimbo]

Just taken the head of my 1098 due to a blown head gasket.

Thought I might as well check the head out whilst it's off. I might of been wrong but I could of sworn someone mentioned the way to test the valve seats is to turn the head upside down and pour petrol in each of the four recesses - whever leaks thru is the culprit, if there is one!

Thoughts...

[bmcecosse]

That's one (rather messy) way. Frankly - i would take them out and inspect the seats - and grind them in. A quick check is to shine a v bright light up the ports (and seal the port off with a rag) in a dark room - and look for any light appearing around the rim of the valve.

[super trimbo]

Nice one BMC - thanks for the tip

[welshrat]

That's one (rather messy) way. Frankly - i would take them out and inspect the seats - and grind them in. A quick check is to shine a v bright light up the ports (and seal the port off with a rag) in a dark room - and look for any light appearing around the rim of the valve.

Nice one BMC, great quick check which I will add to my "do this before moving on list".

[C6Dave]

If the head is off anyway, it's worth regrinding the valves in. Doesn't take that long and it ensures a good seal.

[rayofleamington]

someone mentioned the way to test the valve seats is to turn the head upside down and pour petrol in each of the four recesses - whever leaks thru is the culprit, if there is one!

ps - it's 5 holes (3 exhaust, 2 inlet) leading to the 8 valves.
I tend to use paraffin or white spirit, but petrol is fine too.

I've only ever bothered doing the leak check after seating (lapping) them all. Bright light method is not as good IMHO. Lapping the valves properly should give no leaks however it is a useful check in case one of the valve stems is marginally bent - the valve and seat might look like the surface is fully lapped when it isn't properly seated.

Leak test on a head that's not had the valves reseated - only really useful if one cylinder is low pressure (on compression test) and you want to see which valve on that cylinder (to do a half-job of just replacing one valve rather than a proper job of doing them all)

[bmcecosse]

I agree - the 'bright light' is just a quick/non messy check. If the valves are NOT ground in - the petrol WILL leak through most of the valves - particularly the exhausts.

[MarkyB]

Well worth taking them out unless you have had then out before at least.
It's amazing how much cack can build up on the valves in 20 or more years, think of it a low budget porting!

[beero]

I use paraffin or white spirit as well, slightly less smelly and less of a fire hazard.

[JOWETTJAVELIN]

I used to use paraffin but now always use petrol, it cleans better and dries completely unlike paraffin which tends to leave a greasy residue.

[MarkyB]

Checking that they are sealing OK is like an MOT, a test on the day rather than a guarantee that they will be OK in the future.
If you've had them out and done whatever is needed then they should be good for several years, no need to do them every time the head comes off.

[bmcecosse]

Can't agree with that - definitely should be taken out/carbon grot removed and then reground if the head is off. Again - easiest just to swop on a pre-prepared head and deal with the old head later.

[StaffsMoggie]

If Ive got a head off I always whip the valves out for how long it takes and clean the ports up. If the valves are reusable clean them up in a drill, or get some new ones, then grind them in. Well worth doing.

[welshrat]

Ok, need to buy a valve spring compressor tool, what size, make is required and where best to pick one up?

[bmcecosse]

Here you go.... http://www.ebay.co.uk/itm/Valve-Spring- ... 2c6625cfe3

[JOWETTJAVELIN]

...or you can improvise and use and old hand-operated pillar drill as I did.