Bent valves.. How bent is "bent"

[Lankytim]

BORING RECAP OF EVENTS BELOW.

Some long term forum users may remember my Audi 100 1.8 that lost its cam belt when the tensioner fell to bits. While "repairing" it I timed the cam up 180 degrees out in error and towed the thing around in an attempt to get it started. Its an interference engine and valve damage was a dead cert. I finally timed it up correctly and all it did was pop and fart through the inlet and exhaust when I turned it over. Bent valves then.

I had bought a 2 litre engine from an Audi 80 and converted it to fit the 1.8 Audi 100 using it a kit but the garage that had promised to fit it mucked me about for months before closing down. Total cock up.

Fast forward a few light years and ive lost heart with the replacement 2 litre lump and ordered a reconditioned head from bay- an easy quick fix. It arrived a few days ago and I whipped the old head off today in preperation of the sparky spanking recon head.

REASON FOR POSTING BELOW!

Anyway, when I studied the old head I found there was no apparent damage to the valves and nothing looked bent. The piston CROWNs also looked totally undamaged, although in need of a de-coke. Do valves need to be visably bent for the engine to loose compression? they look arrow straight to me. Any opinions??

[bootsy75hst]

i have an old 4 stroke honda off roader that my dad timed in wrong and bent a valve, it runs but it wont rev past 4 grand i think. i very recently got my head skimed and chambered but when i fitted it it wouldnt run even tho i never touched the timing(a-series engine you see). my mate at worked suggested setting the tappets.........2nd click it fired up. hope this helps.

[Adam]

A bent valve will be visibly bent if it turned over properly on an interference engine.

[Lankytim]

Great, so ive ripped the head off for no reason. I guess I could just not have been looking hard enough?

Alteast I'm putting on a nice GTI head with bigger valves.

[stealthstylz]

You can sometimes only see that they are bent when you take the valves out of your head. From the symptoms you've mentioned i'd say it had bent/dropped a valve.

Matt

[Lankytim]

Anybody know where I can get all the gaskets and bits I need? Rocker gasket, HG, Inlet/exhaust gaskets, All that stuff.

It feels good to at last be doing something with the old barge. Theres pretty much zero wear lip at the top of the bores too!

[<Type desired username here>]

A valve only needs to be bent slightly to cause a misfire. Ideally you should have done a compression check before taking it apart.

Best thing to do is look at the pistons. If you can see valve marks on top of the pistons I would change the corresponding valve.

[Blueyhonda]

On a motor like that i'd recommend euro car parts for cheap bits. As for the valves, if you are taking them out of the old head you can test them just by simply rolling them along the edge of a work bench/kitchen table. If your still unsure, if you have a little go at lapping each valve in with grinding paste you'll soon be able to tell if they are bent by how even the lap mark on the valve seat is. The valves don't have to be visibly bent in order to cause compression problems.

[v8ian]

If you have the head off, the easiest way to check is remove the cam, turn the head valve head upwards on a sheet of white paper,make sure the head is level. then fill each chamber with parafin, then go and have a cuppa and a laydown, better to leave it overnight, go back and shine a torch up the ports and look for wet spots, if you can see seepage, you have a bent valve.

[<Type desired username here>]

I'd go with blueyhondas idea! That way you will know excactly what valves are bent.
The problem with V8's idea is if any of the valve surfaces are burnt or pitted the paraffin will leak past.

[v8ian]

Oct 24, 2008 19:59:52 GMT <Type desired username here> said:

I'd go with blueyhondas idea! That way you will know excactly what valves are bent.
The problem with V8's idea is if any of the valve surfaces are burnt or pitted the paraffin will leak past.

if the valve are letting by, they need looking at anyway, waist of time putting leaking valve into an engine

[Lankytim]

The new recon head is ready to go on so the old one wont be being used. If the valves turn out to be intact ive no idea why the car wouldnt run. Theyve got to be, its an interferecnce engine and I inadvertantly did everything in my power to bend the valves. I didnt do a compression test although the engine sounded decidedly lumpy when turned over. It wouldnt fire up, just pop.

[murran]

10 to 1 you timed it up 180 out (btw if you do this it wont hit any valves on these engines)
but also had the plug leads in the wrong order somehow.

[John]

What is important is that the valve is sealing. I check this by getting a permanent marker pen (marking out blue will do if you have it) and colouring in the valve seat.

I then get a very small amount of fine grinding paste (tooth paste would do..) and lap the valve. Do a bit and then inspect the valve seat. It shoud be a consistent width of removed colouring.

I had a head that had supposedly had recut seats where only 30% of the marking was removed.

[Lankytim]

Cheers for the info guys, When I get chance Ill use some of the methods mentioned to check the old valves. Just need to get the thing back together again now!

When we towed the car around to try and get it started there was definately some nasty metal like noises coming from under the bonnet and the engine kept "snatching", like it was jamming up. Id be amazed if I havent damged something!

Does anybody know the best way to get all the black coke stuff out of the piston CROWNs? It would be nice to have a shiny piston and bore before I reassemble it all!

[Retro_Tony]

If the timing was 180 deg out wouldn't it be firing on the exhaust stroke? The pops would just the the air fuel mixture igniting and blowing straight into the exhaust manifold? I'm sure someone i used to work with did this and just set the ignition timing to suit rather than take the belt back off.

[thewindscreenman]

I bent 1 valve in one of my cvh heads from a sticking follower. Did comp' test to confirm before the head came off but it was only ever so very slightly bent. I put the offending valve in the chuck of my cordless drill, lay the drill on a bench and start it spinning slowly. Place a fixed object next to the valve head and you can just see where it touches in one place & not another as it spins. Very difficult to tell by eye without doing this I found.
I use 3M or scotch pad on piston CROWNs to clean them up but not on the bores !