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        General >> Problems >> Lack of compression - valve removal
        
(Message started by: Mike_Floutier on Aug 10^th, 2008, 5:08pm)

Title: Lack of compression - valve removal
Post by Mike_Floutier on Aug 10^th, 2008, 5:08pm

Ok, I've got low-pressure in my back cylinder (6 bar compared to 13 in the others) - I noticed this after my radiator blew out the other night.

Having got my head gasket off (with much help) and finding this looking ok and the head flat I noticed this "black valve" see - http://www.exhortations.co.uk/images/The%20valves%20top%20is%20front%20cyl.jpg.

Do you think this may be the cause of the low compression? If so, does anyone have any actual experience of removing a valve on the car (as the Ford diagram shows far to many special tools).

Dave suggested pouring paraffin onto the valves to see if the "black" valve was less "tight" that the other cylinders. I used meths instead as I don't have any paraffin; would this matter?

Anyway I do want to get to the bottom of the lack of compression before reassembling the head.

btw does anyone know what a blown head gasket looks like? This is a pic of mine (at the offending cylinder) but I don't really know what to look for http://www.exhortations.co.uk/images/Head%20gasket%20low%20compression%20cylinder.jpg.

Thanks

Mike

Title: Re: Lack of compression - valve removal
Post by Snoopy on Aug 10^th, 2008, 5:40pm

If its BLACK sooty type and quite a thick build up then it suggests to me oil burning with combustion and that would suggest rings, its its the hard type of carbon then more likely petrol/oil and that would be valve seals . Valves are NOT too hard to get off with spring compressor just mind the collets though. if it is valves then reseating and gringing in should do the trick along with perhaps new guides!
A good all round tool box and some valve spring compresor you should be able to manage .

GOOD LUCK

Title: Re: Lack of compression - valve removal
Post by bizzay1 on Aug 10^th, 2008, 5:43pm

I would say that there was nothing wrong with the head gasket, normally from what I have seen, if the gasket is blown there are black trace marks either between cylinders (and pressure from both would be down) or black/water marks between cylinder & water ways(& would give water loss/overheating problems) that valve does look as though it has got very hot, can you force the valve open with something to see if the seat is burnt ??

just seen snoopys reply - surely if it was rings it would be all valves blackened ??

Title: Re: Lack of compression - valve removal
Post by Mike_Floutier on Aug 10^th, 2008, 6:21pm

Good deductive point about "just one valve". I had a good look at it, without compressing it, and the black carbon flakes off pretty easily. It is still pretty black compared to all the others which are this "light, brick dusty" colour.

Assuming I can pick up a spring compressor tomorrow, having compressed the spring, how do you go about getting the valve out and cleaning it? I've not done this before.

Mike

Title: Re: Lack of compression - valve removal
Post by bizzay1 on Aug 10^th, 2008, 6:31pm

If they still use the same method as when I was a lad - once the spring is compressed you will see 2 collets which fit in grooves at the top of the valve stem, these should just come off in your hand so to speak, release the spring tension and the valve will pull out

ohh and it's not just cleaning it, it's lapping it in using an abrasive compound so both the meeting faces, when together, give a gas tight seal

Title: Re: Lack of compression - valve removal
Post by Mike_Floutier on Aug 10^th, 2008, 6:37pm

How do you do that lapping thing? I remember doing something like that on my old motorbike many, many years ago but I think there was a slot for a screwdriver so you could turn the valve to grind it. But these have no slots so how do you turn them I wonder?

Mike

Title: Re: Lack of compression - valve removal
Post by bizzay1 on Aug 10^th, 2008, 6:45pm

http://www.dazecoop.co.uk/10-02-2007/how-to-valve-lapping-on-mini-head

have a read of this Mike, I always used a small sucker on the end of a stick and rolled between the palms of the hands

Title: Re: Lack of compression - valve removal
Post by Mike_Floutier on Aug 10^th, 2008, 10:05pm

Thanks Bizzay, that's really helpful, my challenge will be to get a suitable compressor to deal with the angled, recessed springs.

I deduce from the procedure for "valve stem seal replacement" http://www.fordscorpio.co.uk/manual/engines/dohc2_3/2300ValveSeals.pdf on the site and comments in your "mini" instructions that this must be a common problem.

I'm guessing that what's happened in my case is that the seal has worn out on my "black" valve leading to the oil in the camshaft box (being under pressure) being forced onto that exhaust valve.

I'm also assuming that this leads to the formation of the carbon deposits that we see on the valve and also deposits and maybe wear on the valve mating surfaces which has presumably caused my poor compression (6 bar).

Does this make sense?

Title: Re: Lack of compression - valve removal
Post by bizzay1 on Aug 10^th, 2008, 10:22pm

Was never quite that complex in my day Mike - we had points and condensers and things, - and you could get at the valve stem seals with your fingers ;D

By reading your guess it all seems quite possible

best of luck with the rest of the job

Title: Re: Lack of compression - valve removal
Post by Mike_Floutier on Aug 10^th, 2008, 10:31pm

Thanks! Will let you know how it goes.

Title: Re: Lack of compression - valve removal
Post by gozz on Aug 10^th, 2008, 10:46pm

bizzay.
Snoopy thinks that you could have busted rings on one cylinder I think.Did'nt you do a compression test with oil down your bad bore ? this is how you check for bad piston sealing.Put some paraffin or diesel into your bad cylinder and also into a good cylinder,compare the length of drainage time,you may need to leave it overnight,Best not to use meths for this as it is rather volatile to have in the sump.
Just something else for you to do!
GOZZ.

Title: Re: Lack of compression - valve removal
Post by bizzay1 on Aug 10^th, 2008, 11:11pm

Gozz - it's not me that has the problem - it's Mike, the reason I questioned snoopys suggestion of rings was the picture that mike has a link to - of the four valves in the cylinder in question only one is blackened and looks as if it has got hot, Mike did a test and had 6 bar in that cylinder - the other 3 had 13 bar, hope this clarifies things

Title: Re: Lack of compression - valve removal
Post by Mike_Floutier on Aug 11^th, 2008, 7:00am

Bizzay1 is accurate on all counts.

However your point Gozz about waiting all night for the paraffin (when I get some instead of the meths) is well met, I had poured onto the valves and expected it to drain away instantly.

I'm going for the burnt "black" valve having a failed oil seal, my main challenge (apart from getting parts) is to get a suitable spring compressor for the recessed, angled spring.

My other challenge is that I need to change the seal and get everything back together and the car running (not to mention the new radiator) by tonight ready for work tomorrow.

Any tips for compressing Scorpio springs would be appreciated.

Thanks

Mike

Title: Re: Lack of compression - valve removal
Post by gozz on Aug 11^th, 2008, 8:42am

Mike and Bizzay.
Sorry about the confusion,senility is setting in.Mike I have'nt done much on that engine,but most overhead camshaft heads use a spring compressor with a piece protruding downwards onto the spring cap as against a normal OHV which does'nt.
I have both types,but suppose that's no use to you.You can of course buy one from a tool shop or even Halfords.More expense !
GOZZ.

Title: Re: Lack of compression - valve removal
Post by peteHull on Aug 11^th, 2008, 8:46am

on 08/11/08 at 07:00:01, Mike_Floutier wrote:

Any tips for compressing Scorpio springs would be appreciated.

Thanks

Mike

Poor mans intuition..... ;)

Make a cast of the combustion chamber, ie: line it with clingfilm and pour in plaster/ plaster of paris or polyfiller and leave to set. This gives you a suitable plug to press against.
Put tissue into the combustion chamber and insert the plug, put a board on the head and turn it over. Then using a pair of pliers you can compress the valvespring and remove the collets.... Job done.
This is the way I have carried out this task in similar circumstances in the past.
8)

I hope this helps.

Pete

PS I have a spare cylinder head for sale.... Plug Plug...

Title: Re: Lack of compression - valve removal
Post by Tompion on Aug 11^th, 2008, 9:38am

Mike

A failed valve seal won’t cause lack of compression.
On your picture the valve looks blue rather than black/oily as though it’s got to hot.
The valve dissipates heat via the seat, if the valve’s burnt or pitted or bent then it doesn’t get rid of the heat quick enough, (don’t know but possibly more of problem on gas).
You may need to get the seat recut if it's bad.

Dave

Title: Re: Lack of compression - valve removal
Post by bizzay1 on Aug 11^th, 2008, 10:00am

Thats what I was getting at earlier Dave, when I asked if he could compress the valve spring to have a look at the seat, but while he's at it just as well replace the seal

Title: Re: Lack of compression - valve removal
Post by Mike_Floutier on Aug 11^th, 2008, 10:23am

Ok, thanks guys,

I'm back from All-Parts and Fords loaded with goodies:

1. Spring compressor for recessed springs,
2. Hydraulic chain tensioner plunger,
3. New spark plug
4. Valve grinder & paste
5. Coolant
6. Valve oil seals

and I've got on order for this afternoon:

1. Head bolts
2. Radiator
3. Cam shaft follower - for the "black" valve - it's not actually blue, that's the camera or the printer, it's actually black carbon that you can scrape of if you try.
4.Cam-chain top guide - which I broke getting it off

Right, to work, will let you know how it goes.

THanks again!

Mike

Title: Re: Lack of compression - valve removal
Post by Mike_Floutier on Aug 11^th, 2008, 11:00am

Here are two pics of the black valve - http://www.exhortations.co.uk/images/black%20valve.jpg.

What do you think?

Title: Re: Lack of compression - valve removal
Post by Mike_Floutier on Aug 11^th, 2008, 11:05am

Ok, how do you get the old oil seal off?

Title: Re: Lack of compression - valve removal
Post by bizzay1 on Aug 11^th, 2008, 12:08pm

http://www.fordscorpio.co.uk/manual/engines/dohc2_3/2300ValveSeals.pdf
looking at this the seal is recessed into the head, hence the need for the valve seal pliers also shown, hopefully just a pair if long nosed pliers should do the same job. just grip the seal and it should pull out toward you - have a look at the new ones you have and make sure this is how they fit Mike.

Might help with a little twist as you pull as well (thats the pliers and seal not you Mike hehe)

Title: Re: Lack of compression - valve removal
Post by bizzay1 on Aug 11^th, 2008, 12:11pm

Looking at the valve it does look burnt, how pitted is that ? can't quite make it out but the seat might need recutting before lapping the valve in.

Certainly think you are in the right area which is causing your problem.

Title: Re: Lack of compression - valve removal
Post by bizzay1 on Aug 11^th, 2008, 12:19pm

Just another thought after looking at the instructions for seal replacement, when you come to put the seal back I notice that there is another tool - this could probably be replicated by using a suitable sized 3/8 drive socket on the end of a short extension bar.

Ahhh it's all coming back to me now ;) ;D ::)

Title: Re: Lack of compression - valve removal
Post by Tompion on Aug 11^th, 2008, 1:03pm

Yes, looks like the seat could do with recutting. I think you’ll struggle to lap that valve in without refacing it; you may need a new one.
Is it straight? Just the seat looks a bit odd (might just be the camera angle) – put the valve back in part way & rotate it to see if the valve head's true. Slightly bent valves will often pull in so they pass the paraffin test, but will still cause low compression. Another possibility is that it’s not shutting (not sure if that’s possible with the hydraulic adjusters).

Dave

Title: Re: Lack of compression - valve removal
Post by martin_rowe on Aug 11^th, 2008, 1:27pm

You deffinatly wont 'lap' that valve in, you need to check all the others, worried by the rust on the back of the valve, better get head pressure tested, will need re face also before re fitting, dont do all this work with out the propper checks. if you only do half a job it will come back & haunt you. if the head pressure tests ok, get it re faced, you will need at least 1 valve, get all seats re cut & valves re faced, engineering shop wouldnt charge you much for all that, they would be able to supply all parts at reasonable price also. but make sure head is good first.

Title: Re: Lack of compression - valve removal
Post by Mike_Floutier on Aug 11^th, 2008, 2:31pm

Ok, I'm going to seem to digress slightly to explain my approach. I'm a private hire driver. I have a new car but it is waiting for conversion to lpg. Until it's finished I can't use it for work (time is money - self-employed) so I need the Scorp to run - even on 3 cylinders with 6 bar comp. on No. 4 as I had been doing fairly happily.

I am really only doing this work, a) because I thought my radiator blowout may have been caused by head gasket failure, and b) to get it running well for elling (something I plan to do in 2-3 weeks.

SO,,, I need it running quickly (for work) and, when the new car takes over the reins, I can spend my time in a leisurely fashion (if needs be) doing those excellent sounding task Martin recommends.

Another factor I have to include in deciding how far to go in refurbing is that the car has done 314,000 miles, will sell for peanuts, BUT given the very gentle way I drive (one of my passengers says he wants to have a paper bag to put over his head in case any of his friends see him cos I drive so slowly - hehe!) together with oil/filter/flushes every 3,000 miles, the car could very well go on for ages. Something to think about if anyone is interested. When I've got it going again I'll post my draft e-bay advert.

Anyway, I've lapped the valve as best I can an we'll see how it goes - just waiting for Mr Ford to see if he can find a cam-chain top guide to replace the one I broke

THanks

Mike

Title: Re: Lack of compression - valve removal
Post by Mike_Floutier on Aug 14^th, 2008, 1:29pm

Ok, just to tidy up this thread, as I said, I lapped in the valve as best I could and got the head back on and running.

The result was that the cranking compression in No. 4 cylinder went down from a feeble 6 bar to a very feeble 4 bar - so much for my lapping skill! However, that did demonstrate that I'm on the right track and that this "black" valve is the culprit.

Passengers don't notice it though and I'll be able to continue working the Scorpio until the Lexus returns from the LPG converter at the end of next week.

This brings me to a corollary story. Whilst at the LPG converters this morning, the main man gave me an excellent potted history of upper cylinder lubrication; from leaded fuel to LPG. His point in telling me the story was to convince me of the need for an intelligent system of lubrication for the valves as, in the absence of the additives in unleaded petrol, the valves wear out prematurely. Just such a system is due to be available in the UK in the next couple of months.

This interested me of course, since my Scorp. has just done 250,000 miles on LPG. Maybe Scorp valves are harder that Japanese Lexus valves, I don't know. Anyhow, it made me wonder whether this "black" valve had been a victim of "LPG wear". Also, the guy suggested that it may have worn it's way sufficiently deeply upwards into the head to prevent the hydraulic tappet/cam-follower from allowing the valve to close properly - certainly the new cam-follower I fitted made no difference.

Finally, I'm now looking for a suitable local professional to re-cut the "black" valve's seat for me when the Scorp retires next week. If anyone knows of someone in the Watford area who could do this I'd be very interested; I can take him the head with the valve removed so it should be a simple process.

THanks again!

Mike

Title: Re: Lack of compression - valve removal
Post by Mike_Floutier on Aug 15^th, 2008, 8:31am

Pete Hull, I've pm'd you about your offer of a cylinder head for sale.

Looking closely at the pics of my valves I can see that the "black" valve has receded quite a bit and it's likely that the cam follower is unable to accomodate it's full closure; this is a feature of extended LPG use apparently.

In the circumstances, a new head looks like the best option.

THanks

Mike

Title: Re: Lack of compression - valve removal
Post by Mike_Floutier on Aug 21^st, 2008, 10:07am

Interestingly the cranking pressure for this No. 4 cylinder, having dropped to 4 bar after me lapping the "black" valve in, increased to 8 bar by last Saturday and by this Tuesday was showing over 9 bar.

I've replaced the exhaust manifold gaskets to tidy up the gas monitoring (stinky cabin at lights etc) position but this has made no difference poor idle/low revs - high load performance.

As per another thread, I'm now investigating the CMP (Cam-shaft Postion) sensor as it doesn't seem to make any difference whether it's connected or not which doesn't seem right.

Mike