Leaky valves

dbv8 · Post by **dbv8** » Mon Jan 12, 2015 9:34 am

I removed my heads this weekend ready to fit MLS gaskets.
The car was running sweet with no problems but while the heads were off i took the opportunity to fill the chambers with petrol. The nearsdide head held fual ok. The offside head was a diffent story. 2 chambers leaked quickly and a third took a few minutes.
Ive stripped the heads down and there is obvious signs on some of the valves where the seat hasnt been in contact.

I dont think a simple session with the valve paste and sucker stick will be sufficient.

Do you guys think this can be easily fixed with a trip to the local engine shop for a seat cut? The valves appear to be straight. Is there a clever way of checking they are true?

DaveEFI · Post by **DaveEFI** » Mon Jan 12, 2015 9:42 am

Old way was to make sure they are perfectly clean and roll them on a very flat surafce - like piece of glass.

dbv8 · Post by **dbv8** » Mon Jan 12, 2015 10:08 am

DaveEFI wrote:Old way was to make sure they are perfectly clean and roll them on a very flat surafce - like piece of glass.

Done that. Cant see any movement.
Also to add... i could not feel any play in the guides so they are ok.

stevieturbo · Post by **stevieturbo** » Mon Jan 12, 2015 4:05 pm

Give them a quick lap in with some paste.

it'll cost almost nothing apart from some time and will show if there are any problems.

mgbv8 · Post by **mgbv8** » Tue Jan 13, 2015 9:22 pm

As Stevie says!
Give them a quick lap in and check again. I have to admit that I bought an eezi lap gizmo for the battery drill last year and its the nuts mate. Once you get the hang of using it its great.

Pel

bigaldart · Post by **bigaldart** » Wed Jan 14, 2015 10:30 pm

If the seats are really rough I use a black and decker on the valve stem, slow speed and frequent lifts, be sympathetic and it works fine, I then finish by hand as soon as I have a full contact seat. They hold methanol when I am done. Sometimes put methanol in the inlet and exhaust ports and apply air using a leak down tester through the spark plug hole. Not always easy to hear a slight leak but the fuel in the port bubbling away picks up everything this part is for a quick test on the assembled engine. With the head off you can see if you have a seal easily enough, the fluid test is only to confirm it.

Alan

dbv8 · Post by **dbv8** » Fri Jan 16, 2015 3:21 pm

So ive been using the new Gunson eezi lap.
How long do we reckon this takes?
Ive got a neat even surface on the valve itself. Put the inlets back and filled the ports with water. Number 6 pissed out, 4 and 8 a constant drip and number 2 showed a couple of drops but didnt leak any.

DEVONMAN · Post by **DEVONMAN** » Fri Jan 16, 2015 7:55 pm

A TVR guy once told me that the 500 heads suffer from valve seat distortion. This he said was due to the minimal metal/support between the valves.
He was correct as when I last gave my heads the once over they had the same problem that you have with part of the seat circumference low. I spent hours getting full contact by grinding them in but next time I will opt for getting the seats lightly recut. I have my own cutting tool but it would not touch the hard seat in these heads. The tool worked fine on mini/early ford heads, in the pre unleaded days.

regards Denis

Darkspeed · Post by **Darkspeed** » Fri Jan 16, 2015 8:09 pm

Blue them - it is the only way to ensure you have a seat - seeing a nice grey line around the seat when lapped tells you nothing but you had paste between the two surfaces and if you had a nice thick ball of paste then you could have a large gap.

Did a thread about this somewhere - above you can see a nice Grey lapped seal but when blued there is a gap. Chances are it will hammer in when run but why not start with a decent seal in the first place.

Darkspeed · Post by **Darkspeed** » Fri Jan 16, 2015 8:14 pm

+ test with paraffin

TVR power heads are some of the worst out there as they used to just remove as much material as possible often resulting in porosity in the exhaust ports going to close to water jackets etc. As above you can take out material in the wrong place and leave the chamber poorly supported.

Bluing will indicate where the problems are and if they will be easily resolved with just a smidge more lapping as it will tell you the shape of the contact patch

dbv8 · Post by **dbv8** » Fri Jan 16, 2015 8:39 pm

I dont want to lap these valves any more. I think i will get the seats cut and hopefully the inlets will last another few years.
I had a look at the exhaust valves and think they have seen their days. The seat on them is concave from too much lapping in the past.

Darkspeed · Post by **Darkspeed** » Fri Jan 16, 2015 9:00 pm

Get the valves faced at the same time.

dbv8 wrote:I dont want to lap these valves any more. I think i will get the seats cut and hopefully the inlets will last another few years.
I had a look at the exhaust valves and think they have seen their days. The seat on them is concave from too much lapping in the past.

DaveEFI · Post by **DaveEFI** » Sat Jan 17, 2015 12:39 am

dbv8 wrote:I dont want to lap these valves any more. I think i will get the seats cut and hopefully the inlets will last another few years.
I had a look at the exhaust valves and think they have seen their days. The seat on them is concave from too much lapping in the past.

You surprise me. I've had several very high mileage RV8s, and non has ever needed a valve grind. Not like engines with cast iron heads.

IIRC, the ideal is a three angle cut on the seat so you end up with a very thin ring as the contact point. You can't do that by hand grinding - you make the contact wider and wider the more you take off.

unstable load · Post by **unstable load** » Sat Jan 17, 2015 5:31 am

3 angle cut is the way to go if you are going to re-cut the seats.
The valves should be salvageable too, with a regrind, so that will save you some pennies.

DEVONMAN · Post by **DEVONMAN** » Sat Jan 17, 2015 8:55 am

Dave EFI wrote :- You surprise me. I've had several very high mileage RV8s, and non has ever needed a valve grind. Not like engines with cast iron heads.

It's only the TVR 500 big valve heads that suffer from this problem.
There seems to be insufficient support to the valve seat ring after the massive porting and opening out that TVR do to these heads.

Regards Denis