No compression

[sh0dan]

RE: 1972 Spitfire Mk 4

A novice question I'm afraid. Whats the best/cheapest thing to do when looking at repairing or replacing a cylinder head?

I have no compression on cylinder 3 and its a little low on cylinder 2. Should I buy a new unleaded head, second hand leaded head or should I look at repairing the existing one? How easy is it to remove the head? What type of repairs could I consider?

I’m expecting to see that the exhaust valve has receded, based on my research. I understand its common on cylinder 3.

Im nervous about not getting an unleaded head, people say that heads which havent got a build up from leaded petrol are far more likely to fail. For this reason hardened valve seats seem like a necessity, with four gears and no overdrive it does get a little bit of a hammering on motorways.

[TimW]

Removing the head is a straight forward job.  Follow the haynes manual and all will be fine.  if you do alot of miles and use the car alot then yes bite the bullet and go hardened valve seats.  Many people will say they are not needed but they are quite cheap these days if you go standard exchange or get your head done at a local engine builder. At least it won't happen again!  I don't run hardened seats on the gt6 mainly because they havn't receded yet but when they do i shall go hardened seats.  The lack of compression may not be valve  seats so i would pull the head and have a look. Post some pics of it on here so we can all have a look.

[bob dunn]

dont  know  but what is the stuff that you put in the petrol to loosen the piston rings

[sh0dan]

bestquality03: Thanks, i will get it off and post some images.

bob dunn: I have always used "Castrol Valvemaster Plus Fuel Additive", but I guess nothing is as good as the real thing?

[TimW]

Where do you live? Why don't you put up a signiture someone may be local and may well offer to give you a hand

[sh0dan]

bestquality03: Thanks, Im near norwich and I'm sure if I need it I can ask a favour from the great people at the club. I'll see what I can do first, getting the head off does sound easy.

[sh0dan]

Well except the bit that says "use plenty of releasing fluid around the studs and apply firm taps with a SOFT-faced hammer or mallet to shake the head free. It will eventually come off." [haynes restoration manual]. Which translated sounds like "its going to be a sod to get off"  ;)

[Russell]

sh0dan,

Before you take the head off, check your valve clearances first. If there is valve seat recession, you may find there is no gap between the rocker and the valve, so the valve is not closing properly.

If that's the case, you may be able to adjust it out and carry on quite happily for a few more thousand miles.

Russell.

[JohnD]

dan (?),

Before you take off the head, use this test.
Squirt/pour a little engine oil into the offending cylinder.
Try tham all, why not?
Repeat the compression test.
If the pressure rises, then the rings are at fault.
If it doesn't, then the valve is your problem.

Then, to take off the head.
Take the studs out!
It's often that the head has siezed on a stud, rather than bonded to the block (Am I overdoing the alliteration tonight?).
And it's good practice to replace the studs anyway.
Once the studs are out, then those soft headed hammer blows can be much more effective.
It can be still less than easy though.

John

[sh0dan]

Russell: I'll try and look at that, im not 100% what i'm looking for but will attempt to compare that section of the rocker gear to other cylinders?

John: No Mike :) Are you able to clarify how I "Squirt/pour a little engine oil into the offending cylinder" with the head still on. Sorry probably a stupid question but I'm very much a novice still.

Thanks both, all input appreciated!

Mike

[sh0dan]

John found this information, I assume this is what you are suggesting?

"First you ought to identify the cause for low compression. You could carry out a leak-down test or a wet compression test.
A wet compression test is easier to do. Equip yourself with a compression tester, plug removal tools, some engine oil and an assistant. Remove one plug from each cylinder.
1) Measure compression on each cylinder and make a note of each reading.
2) Pour a couple of tablespoons of engine oil into each cylinder through the spark plug holes.
3) Crank engine on starter for 2 - 3 seconds. The oil will then wet the cylinder bores and temporarily improve piston to cylinder seal.
4) Measure wet compression on each cylinder.
5) Compare dry and wet readings. A significant increase in compression on the low cylinder indicates you have a piston ring problem. No increase indicates you have a leaking valve.
Fixing a leaking valve is easy but does require removal of the cylinder head. It will cost you an arm and a leg unless you do it yourself. I guess no less than 500 pounds if done by an independent garage - if you can find one." [http://www.smartz.co.uk/showthread.php?p=84614]

Thanks again

Mike

[Russell]

sh0dan wrote:

Russell: I'll try and look at that, im not 100% what i'm looking for but will attempt to compare that section of the rocker gear to other cylinders?

You need a Haynes Workshop Manual, (rather than the Restoration Manual), that explains how to do it. It's not tricky. My unscientific method is, take off the rocker cover, flick the engine over (don't start it) until the exhaust valve of cylinder 3 is at the top of it's travel. If you then wiggle the rocker, there should be a little bit of play between it and the top of the valve. If there's no play and it's tight, then you need to adjust it.

I've been frantically googling for the past few minutes to see if anyone has a web page on how to do it - but have found nothing. There must be one out there somewhere.

I've had to do this on the 2000 every 10000 miles or so. Eventually the recession will be so bad I will have to get the head rebuilt.

Russell.

[willows40]

mike
if you come to the meeting monday come and have a chat about it

cheers andy

[rossybrown]

Where in Norwich are you mate?  I'm north, near Coltishall and your welcome to borrow my Haynes manual but I would recommend getting one if you're keeping the car.

[sh0dan]

rossybrown: Thanks for the offer but I’m good. I have an original and a Haynes workshop manual but in this case the restoration manual had pretty pictures :)

Andy: Will do thanks. No clashes this month so I will be there.

[sh0dan]

Russell: Forgot to say thanks "I've been frantically googling". I'm going to have a look at that and the wet compression check today.

I should probably post more often, I seem to learn a lot more than reading a book! Thanks everyone.

[JohnD]

RussellBanyard wrote:

You need a Haynes Workshop Manual, (rather than the Restoration Manual), that explains how to do it. It's not tricky. My unscientific method is, take off the rocker cover, flick the engine over (don't start it) until the exhaust valve of cylinder 3 is at the top of it's travel. If you then wiggle the rocker, there should be a little bit of play between it and the top of the valve. If there's no play and it's tight, then you need to adjust it.

Russell.

Gods' teeth, Russell, you may not need a workshop manual, but you are in desperate need of a set of feeler guages!
Of course if you are a time served motor mechanic and engineer with thousands of hours of engine building..............

John
(who isn't)

PS googling often needs you to know the right words to google for!
Try:
http://www.aa1car.com/library/compression.htm
http://www.pumaracing.co.uk/comp.htm
http://www.dansmc.com/compression_test.htm (bikes, but same difference)
http://www.ehow.com/how_4508304_perform-compression-test-engine-nissan.html
http://www.waybuilder.net/sweethaven/MechTech/Automotive01/default.asp?unNum=2&lesNum=7&modNum=6

and that's just the first page of Google's "Oil compression test"!  J.

[Llessur]

Before doing anything else I would spend (literally) a couple of quid on a set of feeler gauges and check your valve clearances properly - any Haynes manual or numerous online resources should tell you how to do this. It's hugely simple and will only take about 15 mins - you need to make sure it's done properly as when you're talking about a few thou of an inch just wiggling won't tell you anything.

If you're lucky this will solve your problem but if not then at least you know you're not going to shoot off down the very expensive and time-consuming road of engine rebuilds unneccessarily.

Just my humble opinion but seems like common sense to me  ;)

Good luck!

[sh0dan]

Hi All,

Quick update based on your feedback and advise at our triumph meeting.

The valve clearances were a little out so I used the haynes owners workshop manual and this great video (http://www.youtube.com/watch?v=fezXUwVfH7U) to adjust them. No noticeable impact on compression test, but a very good learning experience.

While performing the compression test I didnt have the accelerator pressed to the floor, so did this. No noticeable impact on compression test, my highest compression reading is on cylinder 4 and thats still 30 PSI.

I performed a wet compression test, "Pour a couple of tablespoons of engine oil into each cylinder through the spark plug holes" - sounded easier than it was :) ... WOW!! compression on all cylinders doubled, even cylinder 3 which wasnt giving a reading went to 25ish PSI. So all I have to do is stop every few meters and pour oil in right :) There was a difference in sound as well, engine sounded stronger.

So a £250 cylinder head wouldnt have done me a lot of good I suppose, just as well I know I'm usually wrong! Based on everyones advise I'm now looking at worn piston rings I assume.

Would worn piston rings also cause an increase in oil leaking? I think I read something a while ago about replacing a piston ring and it started "remove and dismantle the engine..."!?

Thanks again everyone thats helped.

Mike

[Llessur]

sh0dan wrote:

Would worn piston rings also cause an increase in oil leaking?
Mike

Would definitely cause an increase in oil *burning* - as the worn piston rings will allow oil past and into the combustion chamber to be merrily burnt off. Have you noticed any blue smoke from the exhaust - especially under acceleration?

As for replacement of the rings - I've not actually done it myself but it will be far easier with the engine out but nothing to be too scared of. Would also be a good opportunity to inspect the bores for wear, replace the big end bearings etc.

Go on - it'll be fun ;)

I guess the other option would be to source a known good engine from eBay or similar. If you're not too keen on embarking on a rebuild then this would be far easier - just borrow/hire an engine crane, whip out the old one and slot in the new. Apart from a few ancillaries (clutch, fuel, dizzy/ignition, exhaust etc) it's literally a case of undoing 20 or so nuts/bolts. As long as you do actually get a good used one (shhhh Clive ;) ) then this should be a good bet and allow you to get the car back on the road quicker. Set you back a max of £150-£200 I reckon. Probably less. Plus a great way to really get to know your car.

Just a thought - have you thought about going down the six cylinder route? I just have and would highly recommend it!  8)

[sh0dan]

Hi,

No smoke, occasionly a pool of oil forms on top of the exhaust manifold underneath a small hole of some kind between the 3rd and 4th cylinders. There is also evidence of something spraying on the underside of the bonnet, I originally thought that this was the result of a blocked float chamber I cleared but I have to admit it looks more like oil.

In addition I havent located where oil is dripping on the floor from but there is a new leak somewhere.

Taking it out does interest me and if I knew I might have to get a new engine there would be nothing to loose, quite a big leap from the things I've done so far. I'll have to think about it, I also think I would have to admit defeat on getting it running for the rest of summer.

A new engine has crossed my mind, but then I figured I couldnt be sure the same thing wouldnt happen again unless it had been rebuilt.

I have no idea whats involved in a bigger engine, but I have no real need for it. If I could alter the car in some way, not broken would be on the top of the list and an overdrive in second place.

Cheers, I need to think about this

Mike

Llessur wrote:

Would definitely cause an increase in oil *burning* - as the worn piston rings will allow oil past and into the combustion chamber to be merrily burnt off. Have you noticed any blue smoke from the exhaust - especially under acceleration?

As for replacement of the rings - I've not actually done it myself but it will be far easier with the engine out but nothing to be too scared of. Would also be a good opportunity to inspect the bores for wear, replace the big end bearings etc.

Go on - it'll be fun ;)

I guess the other option would be to source a known good engine from eBay or similar. If you're not too keen on embarking on a rebuild then this would be far easier - just borrow/hire an engine crane, whip out the old one and slot in the new. Apart from a few ancillaries (clutch, fuel, dizzy/ignition, exhaust etc) it's literally a case of undoing 20 or so nuts/bolts. As long as you do actually get a good used one (shhhh Clive ;) ) then this should be a good bet and allow you to get the car back on the road quicker. Set you back a max of £150-£200 I reckon. Probably less. Plus a great way to really get to know your car.

Just a thought - have you thought about going down the six cylinder route? I just have and would highly recommend it!  8)