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Cylinder Head rebuild


colinnorth

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I am about to remove the cylinder head on my BMC 1.5D because the rearmost stud (that hold the rear section of the exhaust manifold) has sheared off. Luckily I found it in the drip tray otherwise I would not have known it had sheared. The engine has no other known problems. I have found a local Engineering works that specialises in this work.

 

When I remove the head I will also refurbish the injectors.

 

Q1 - once the injectors have been refurbished, do they need to be pre-filled with diesel or will the connection of the diesel feed pipe blast the air out of the injector hole?

 

Q2 - as it is some 40 years since I last removed/replaced a cylinder head (did it many times in youth with Morris minor/MGB/VW etc.) - when you put the head gasket on to the block, do you oil/grease the surfaces of the gasket to get a better seal? Or am I just being senile and not remembering correctly from all those years ago?

 

Q3 - what's the likelihood I will need the head skimmed. It is a 1980 model and probably not been off for 20 years or so.

 

TIA

Colin

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Q1 - no

 

Q2 - no. However, BMC 1.5 gaskets do seem to leak water so some judicious use of sealant around the waterways would be sensible

 

Q3 - just do it. And get the valves sorted too, it's well past time for a decoke. And the valve guides, and check the rocker shaft for wear and grind the dents out of the rockers so they don't wreck the guides

 

Q4 - yes, you need to use a crowsfoot spanner to torque the nuts up under the rocker shaft

 

Richard

 

 

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**** WARNING *****

 

Get a look at a parts list or exploded view in the manual.

 

The injectors fit into a sort of inverted top hat heat shield thing that is "loose" in the head but they often lift out on the injector nozzle. Make sure you take any that do that off.

The nozzle sits on a sort of crimped flat washer thing in the hat shield (atomisation washer). this really should be replaced each time the injectors are removed.

 

If you look down the injector hole and see a small land at the bottom of the hole and about a half inch hole in it the heat shield is missing. If the hole is less than 1/4 inch the heat shield and probably the atomisation washer are in place.

 

Order of fitting down the hole in a bare head:

 

1. large diameter but thin section copper washer sitting on the land.

2. Heat shield.

3. Atomisation washer down the heat shield.

4. larger section copper washer around injector nozzle or down the hole sitting on top of the heat shield.

 

Also remember to decarbonise the glow plug holes. I think it needs a 7/64" drill bit in a HAND drill.

 

Q1 - When it is all back together bleeding the system will sort the injectors.

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While the heads off pour a little  ordinary Redex UCL onto each piston crown, it'll soften the carbon right up and next day you''ll be able to just wipe it out with a clothe.  ''Fetch a clothe Granville''.  Its better than scraping at it.

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Thanks All for your detailed replies for which I am very grateful.

I have a copy of the manual and will have it to hand.

The only thing worrying me now is the ‘Crowsfoot’ spanner/socket. I have a torque wrench but will have to look for said crowsfoot spanner.

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2 minutes ago, colinnorth said:

Thanks All for your detailed replies for which I am very grateful.

I have a copy of the manual and will have it to hand.

The only thing worrying me now is the ‘Crowsfoot’ spanner/socket. I have a torque wrench but will have to look for said crowsfoot spanner.

Machine Mart: https://www.machinemart.co.uk/p/clarke-crows-foot-imperial-wrench-set-8-piece/

 

Richard

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I am very naughty sometimes with BMC heads. I pull all the nuts down with the rocker shaft off, quickly fit the shaft and pull all that I can get to without the special spanner again. Clean and oil all the threads so you get an accurate torque setting.

Its a rough method but it has never got me into trouble-----yet! I usually give the impossible to get at ones an extra 10 ft/lbs before fitting the shaft.

 

Get everything on the head done whilst it is off, valve seats, stem seals, decoke, all new copper washers, injectors reset, rocker faces, heater plugs cleaned out etc.

Fit 4 new injector top hats its not worth using the old ones, they do eventually break up.

 

As to skimming the head, remember it has hardened combustion chambers which are meant to protrude a few thou from the face, skimming makes them flat and they no longer compress the gasket as they should. Technically the head should be skimmed with them removed and then chambers refitted and skimmed to the correct height. I have never found anyone that does this.

For this reason I run a straight edge over the head and if I can't detect any bow over a few thou with feeler gauge I don't skim. I always run a thin smear of blue Hylomar around the waterways on the head and the block on the basis that it does no harm and may prevent a weep.

Edited by Boater Sam
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If you like doing jigsaws you can do the job properly without a crows foot given enough space in front or behind the engine.

Fit the head nuts and rocker shaft but only nip the nuts up enough to secure the rocker shaft pedestals. Then take the split pin out of one end of the shaft and draw it out carefully putting each spring, spacer,and rocker in order in a tray. Then torque up the head nuts and fully tighten the pedestal nuts. Finally push the shaft back in threading each piece onto it in turn and adjust the valve clearances. Do it all again when the engine is nice and hot and again 100 hours or so later - probably easier to buy a crows foot.

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Very good advice in the last couple of posts. I also do not skim heads unless I can find a low spot but it can be hard to find a straight 'straight edge' a combination of all the 'straight' edges in the shed usually gives a good indication and a bit of oil or engineers blue on a flat sheet of glass will also give a few clues. I had a MK1 fiesta that got through head gaskets frequently. Head was fine but the top of the block was not. No idea how that happened. B****** thing.

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3 minutes ago, Bee said:

Very good advice in the last couple of posts. I also do not skim heads unless I can find a low spot but it can be hard to find a straight 'straight edge' a combination of all the 'straight' edges in the shed usually gives a good indication and a bit of oil or engineers blue on a flat sheet of glass will also give a few clues. I had a MK1 fiesta that got through head gaskets frequently. Head was fine but the top of the block was not. No idea how that happened. B****** thing.

Some engines demand liner protrusion so skimming the block is not possible and the protrusion makes  using a straight edge over the whole head difficult. Lucking I seem to recall the 1.5 has zero liner protrusion because it does not use liners.

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6 minutes ago, Tony Brooks said:

Some engines demand liner protrusion so skimming the block is not possible and the protrusion makes  using a straight edge over the whole head difficult. Lucking I seem to recall the 1.5 has zero liner protrusion because it does not use liners.

Correct. It's the pistons that protrude on a 1.5

 

Richard

18 hours ago, colinnorth said:

I am about to remove the cylinder head on my BMC 1.5D because the rearmost stud (that hold the rear section of the exhaust manifold) has sheared off.

You do know that you can drill out a stud and helicoil a head without removing it

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7 minutes ago, RLWP said:

You do know that you can drill out a stud and helicoil a head without removing it

 

I was thinking this myself, or drilling the old stud out meticulously and clearing the existing thread with a tap.

 

One issue may be access but preferable to disturbing the head gasket.

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14 minutes ago, RLWP said:

Correct. It's the pistons that protrude on a 1.5

 

Richard

 

Only if something extremely dramatic has happened to the engine at very high revs!

 

Its a flat Ricardo Comet head, no recess. You are confusing it with a Ford?

3 hours ago, Tony Brooks said:

If you like doing jigsaws you can do the job properly without a crows foot given enough space in front or behind the engine.

Fit the head nuts and rocker shaft but only nip the nuts up enough to secure the rocker shaft pedestals. Then take the split pin out of one end of the shaft and draw it out carefully putting each spring, spacer,and rocker in order in a tray. Then torque up the head nuts and fully tighten the pedestal nuts. Finally push the shaft back in threading each piece onto it in turn and adjust the valve clearances. Do it all again when the engine is nice and hot and again 100 hours or so later - probably easier to buy a crows foot.

You have more patience than I Tony.      5/8 AF Crowfoot or cut a ring spanner and weld an extension at 90 degrees.

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1 minute ago, Boater Sam said:

Only if something extremely dramatic has happened to the engine at very high revs!

No, if you check you'll find 1.5 pistons pop up above the top of the block. I have measured them in the past and skimmed the piston crown to equalise them

 

Richard

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Ah, only into the gasket space yes.

I had images of busted cranks and stretched rods!

You equalise on a diesel? Is that not  a bit OCD? I used to do full stroke and chamber equalisation but only on a petrol race engine. Those were the days. 12 to 1 stoichiometric mixtures with 15 to one compression ratios.

 

Would love to build a 1.8D fully balanced, they are a mile out usually.

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16 minutes ago, Boater Sam said:

Ah, only into the gasket space yes.

I had images of busted cranks and stretched rods!

You equalise on a diesel? Is that not  a bit OCD?.

No, it isn't in the slightest bit OCD, it's standard practice on most of them. Listers and Petters have their heads shimmed to get equal compression

 

Richard

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Thanks again for all input.

I have now ordered the 'crowsfoot' sockets

Gathered the valve seating gear, found the 40+ year old torque spanner etc., got gasket set, washers and thingies for injectors.

Will certainly do the injectors.

Have considered doing stud removal in-situ but would not be easy. Also, knowing that head has not been removed for 20+ years am curious as to the condition of things inside. The condition of the engine has not given me cause for concern up to now. Good starting, Quiet running. Only one tappet slightly louder than the rest which gives a certain rhythm to things (yes I will attempt to sort that out). Fuel consumption excellent at about 1 L per hour. Virtually no oil loss between oil changes.

 

Many thanks to all, Colin

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19 minutes ago, RLWP said:

No, it isn't in the slightest bit OCD, it's standard practice on most of them. Listers and Petters have their heads shimmed to get equal compression

 

Richard

But those are proper engines that mere mortals like me don't get to work on, not BMC junkers. I've rebuilt lots of 1.5s and 1.8s and never machined any crowns.

Did have a customer a long while ago with an ex firms Cortina 1.3 Xflow that they had put a short motor in before giving it him as a retirement present.

Unfortunately it was a flat head cross flow and they used early flat top pistons instead of bowl in crown too! Hate to think what the compression ratio must of been. They had retarded the ignition massively.

When we tuned it, boy, did it pink!

Found him a chambered head to sort it out.

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Just now, Boater Sam said:

But those are proper engines that mere mortals like me don't get to work on, not BMC junkers. I've rebuilt lots of 1.5s and 1.8s and never machined any crowns.

 

Fair enough, I think I have only done it a couple of times. I do always check the pop up 

 

In theory the Lister Alphas have different thickness head gaskets to set the compression (which is much, much more important on a diesel than a petrol). In practice, you can usually only get the thickest one. The Alpha also has pop-up pistons

 

Richard

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Set and check the tappets before you tear it down, if one still taps badly, check the cam followers, easy to do in the side chest whist the head is off,  as this motor has a habit of follower wear.

Also easier whilst the head is off, clean the skew drive gear and filter. they get neglected.

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On 08/03/2019 at 12:27, Boater Sam said:

Set and check the tappets before you tear it down, if one still taps badly, check the cam followers, easy to do in the side chest whist the head is off,  as this motor has a habit of follower wear.

Also easier whilst the head is off, clean the skew drive gear and filter. they get neglected.

 

On one car engine I had the followers were rather domed and flatted them on an oil stone. I'm not sure if it made much difference as what was really worn was the camshaft!

 

Still, if you can get them out it's worth doing so and having a look at their state.

 

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The early Fraud ohv 997 and 1340 engines as fitted to Anglia 105e and the early Classic used cast top hat flange cam followeres which sometimes a bit of the flange would snap off and the follower rotate so the break was across the cam and then in a very short time would actually machine the cam into a round shape, so perfectly it looked like a lathe had done it. it was always an inlet valve cam follower that did it for some reason. The car would come in on 3 cylinders popping through the carb like a machine gun. The followers were inserted into their guides from below before the camshaft is fitted.

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  • 4 weeks later...

Job now completed. Broken stud removed & helicoil fitted. Head stripped & cleaned. Valves reground (not really needed). Head refitted, tappets done. Glowplugs checked by applying 12v - all glow OK. Injectors replaced by CAV Reconditioned items as supplied by Calcutt. Diesel blown through injectors with glowplugs out to check for diesel vapour OK. glowplugs 12V checked in situ both by voltmeter on glowplugs and by 12V meter needle falling slightly indicating current drawn. So I do not consider there is any glowplug problem.

Upon startup - glowplugs for 40 seconds, attempt to start - clouds of un-burnt diesel. Reapply glowplugs startup OK, engine cughs into life and then immediately runs beautifully. Tappets quiet, all seems OK

Next day:  glowplugs for 40 seconds, attempt to start - clouds of un-burnt diesel. Reapply glowplugs startup OK, engine coughs into life and runs beautifully. Re-start engine later in the day whilst still slightly warm, immediate start, no white un-burnt diesel cloud.

This palaver seems to be pretty much how it starts every day now. 1st attempt, clouds of white, 2nd (or maybe 3rd) attempt will start with a cough and run really sweetly. Will restart (say) after lunch stop or lock/tea break etc.

 

Any thought on this one? Much appreciated.

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Unburnt diesel, You'd sort of think it was timing or compression really. If the timing has not been fiddled with and the injectors are reasonably ok then I think I would recheck valve clearances then maybe check electrical connections to the glow plugs.

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