BMC 1.8 head gasket re torque or replace?

[Nick Bys]

Hi all, 

This is my first post, been a voyeur of the forum for a couple of years through Google searches sending me here, but now I’m in need of some of you guys knowledge directly. 
 

I have a 1978 Cambridge Carrington 27 with a 1.8 BMC which starts and runs great, was overhauling the whole cooling system yesterday (Raw and closed) when I ran up to temperature I noticed what looked to be combustion gases creeping from the head below the injector rail. 
One of the injector nuts had a little leak which I nipped up and all was well, thought that maybe it was just the diesel residue burning off as it hit the hot block. On close inspection it looks as tho the head gasket could be letting by (see video)

any thoughts on this would be much appreciated. 
The video is really short but it shows what’s looks to be bubbling at the gasket, needs to be played at 720p to clearly see the detail. 
 

TIA

 

Nick

Edited January 26, 2022 by Nick Bys
Playback quality

[Tony Brooks]

Well done for spotting that. If it has shown no signs of overheating, loss of coolant, or oil in the coolant I think, if it were mine, I would keep an eye on it to see if and how it develops.

Edited January 26, 2022 by Tony Brooks

[pete.i]

Definetly little bubbles there so the head gasket is leaking but it is miniscule at the moment. It will get worse the question is when. As Tony says I would leave it for now but it will get worse sooner or later. I would think that as the gasket is already leaking re-torquing the head wont do much if anything and could make matters worse.

[Nick Bys]

Hi Tony, thanks for taking the time to reply. 
 

No signs of concern in the year I’ve had it, it’s possible it could’ve lost around 1/2ltr of coolant from the exchanger but that’d be assuming it was full up when I last checked in the autumn. For which I can’t honestly remember.
 

No oil in the coolant, no sign of water in the oil or oil loss. 
 

oil pressure and temperature have always been spot on, starts on the button even in the last couple of weeks at sub zero temps. 20 seconds of glow plug and will start in 2-3 seconds of cranking. 
 

This is the first year I’ve managed to start prepping for the season early to avoid missing the good bits of boating when the weather allows. Also hoping to cruise to the upper Thames in the summer hence the thorough going over and renewal of suspect Parts and hoses etc. 

 

I’ll try and get a good days cruising in the next couple of weeks and observe the fluid levels. Also De-grease the block to see if any and how much is leaking by. 

I’m sure I read somewhere about re torquing the Bmc heads but can’t for the life of me find it, did I imagine that?

 

Nick

 

 

 

 
 

1 minute ago, pete.i said:

Definetly little bubbles there so the head gasket is leaking but it is miniscule at the moment. It will get worse the question is when. As Tony says I would leave it for now but it will get worse sooner or later. I would think that as the gasket is already leaking re-torquing the head wont do much if anything and could make matters worse.

Thanks Pete 👍🏼

[Tracy D'arth]

I would not worry unduly about this.

Certainly not to the extent of immediately replacing the gasket on an engine that is running OK.

BMC did have some porous  gaskets that breathed at the edges. The under warranty cure was to get the motor hot and paint the joint lines with their green paint as it cooled down, hopefully drawing the paint into the asbestos core.

 

I would retorque the head, it is a service interval requirement after all.

 

Loosen  by half a turn and retorque to 75 to 80 ft/lbs one bolt at a time working the sequence in the manual from the centre outwards. The manual is on line at https://calcuttboatsshop.com/BMC-18-Workshop-Manual-PDF-Download   Or you may find the free one elsewhere.

You will need the special tool or a 11/16" crowfoot wrench to do the bolts under the rocker shaft. Do not remove the shaft to get at these, it is vital to maintain the bolt pressures.

 

Then just keep an eye on it, with fingers crossed.

[Tony Brooks]

2 minutes ago, Tracy D'arth said:

You will need the special tool or a 11/16" crowfoot wrench to do the bolts under the rocker shaft. Do not remove the shaft to get at these, it is vital to maintain the bolt pressures.

 

I have often thought that if you have space and liked doing jigsaws you could take the shaft out of the posts and get a socket on those center nuts but 10:1 in re-torquing a post would move slightly so you can't get the shaft back through the posts. If anyone tries this make sure the shaft goes back in the right way round. Only one post has a drilling for the oil feed to the shaft and thus rockers.

[Tracy D'arth]

3 minutes ago, Tony Brooks said:

 

I have often thought that if you have space and liked doing jigsaws you could take the shaft out of the posts and get a socket on those center nuts but 10:1 in re-torquing a post would move slightly so you can't get the shaft back through the posts. If anyone tries this make sure the shaft goes back in the right way round. Only one post has a drilling for the oil feed to the shaft and thus rockers.

I have never tried this, sounds fraught with difficulties.  Easy enough to get a crowfoot. I have seen them fabricated from an old ring spanner but they need to be strong to resist the torque.

[Nick Bys]

22 minutes ago, Tracy D'arth said:

I would not worry unduly about this.

Certainly not to the extent of immediately replacing the gasket on an engine that is running OK.

BMC did have some porous  gaskets that breathed at the edges. The under warranty cure was to get the motor hot and paint the joint lines with their green paint as it cooled down, hopefully drawing the paint into the asbestos core.

 

I would retorque the head, it is a service interval requirement after all.

 

Loosen  by half a turn and retorque to 75 to 80 ft/lbs one bolt at a time working the sequence in the manual from the centre outwards. The manual is on line at https://calcuttboatsshop.com/BMC-18-Workshop-Manual-PDF-Download   Or you may find the free one elsewhere.

You will need the special tool or a 11/16" crowfoot wrench to do the bolts under the rocker shaft. Do not remove the shaft to get at these, it is vital to maintain the bolt pressures.

 

Then just keep an eye on it, with fingers crossed.

Thanks for this,

 

I’ll source the crows foot and re-torque over the weekend.

 

I already have the manual you linked, I knew it’d come in handy one day

 

out of interest do any of you guys know where to source a replacement tacho sender (tin can) looking version for a yazaki tacho with two blue wires?

 

Thanks again

 

Nick

 

[Tony Brooks]

36 minutes ago, Nick Bys said:

out of interest do any of you guys know where to source a replacement tacho sender (tin can) looking version for a yazaki tacho with two blue wires?

 

Short answer no, but if it is for the boat then unless a mechanical tacho was ever fitted it is probably an inductive sensor that senses the presence of steel close to the sensor tip. It normally produces one pulse per steel tooth or finger. If it is screwed into the flywheel housing or if it is close to some extra steel fingers on the front pulley it is probably an inductive sensor. If it is positioned in a way that suggest it is driven by a  gear then it may well be a generator producing a voltage proportional to  speed. I don't think you would find it easy to get one of those.

 

If it is inductive then Wema list one at just shy of £50 that may or may not work and you might have to fabricate a bracket. I also suspect that an ABS sensor  from a car scrappy could be persuaded to work

 

Some webpages suggest a revcounter using an inductive sensor can also be driven form the W terminal on the alternator or a phase tap if it does not already have a W terminal. However you would need the instructions for re-calibrating the revcounter. A phase tap could be fitted to any alternator.

 

There is not much more to an inductive sensor than a permanent magnet and a coil so I am not so sure what could go wrong unless it has suffered mechanical damage. Their tip also need to be pretty close to the teeth or fingers that trigger them so  it may need adjusting.  Wema say their tip needs to be about 1mm away from the teeth/fingers.

 

Any chance of a photo so we can see it and maybe what is wrong with it.

 

Unless a wire has fallen off I would stick a multimeter set to Hz (if yours has that function) on the two wires and rev the engine. If the Hz goes up and down with the engine than the sender is probably OK, look at the other cables on the actual meter in case it has lost ts feed or negative.

[RLWP]

1 hour ago, Nick Bys said:

Thanks for this,

 

I’ll source the crows foot and re-torque over the weekend.

 

 

Before I had a 'proper' twelve point offset socket, I used one out of a set like this:

 

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

 

Slightly more faff as you may have to keep turning the 'spanner' over as you tighten. Otherwise, works fine

 

Richard

[Nick Bys]

That’s the set I just picked up from machine mart 👍🏼

[Nick Bys]

3 hours ago, Tony Brooks said:

 

Short answer no, but if it is for the boat then unless a mechanical tacho was ever fitted it is probably an inductive sensor that senses the presence of steel close to the sensor tip. It normally produces one pulse per steel tooth or finger. If it is screwed into the flywheel housing or if it is close to some extra steel fingers on the front pulley it is probably an inductive sensor. If it is positioned in a way that suggest it is driven by a  gear then it may well be a generator producing a voltage proportional to  speed. I don't think you would find it easy to get one of those.

 

If it is inductive then Wema list one at just shy of £50 that may or may not work and you might have to fabricate a bracket. I also suspect that an ABS sensor  from a car scrappy could be persuaded to work

 

Some webpages suggest a revcounter using an inductive sensor can also be driven form the W terminal on the alternator or a phase tap if it does not already have a W terminal. However you would need the instructions for re-calibrating the revcounter. A phase tap could be fitted to any alternator.

 

There is not much more to an inductive sensor than a permanent magnet and a coil so I am not so sure what could go wrong unless it has suffered mechanical damage. Their tip also need to be pretty close to the teeth or fingers that trigger them so  it may need adjusting.  Wema say their tip needs to be about 1mm away from the teeth/fingers.

 

Any chance of a photo so we can see it and maybe what is wrong with it.

 

Unless a wire has fallen off I would stick a multimeter set to Hz (if yours has that function) on the two wires and rev the engine. If the Hz goes up and down with the engine than the sender is probably OK, look at the other cables on the actual meter in case it has lost ts feed or negative.

 

[Nick Bys]

I do have voltage at the sender and at the tacho albeit very little 0.23v at tickover 0.65 at guessing 2500rpm actual engine speed. This displays 300rpm and 700rpm respectively on the tacho gauge. 
 

unfortunately I don’t have Hz on my multimeter, could borrow one to check the output tho. 
 

Nick 

[Tony Brooks]

2 minutes ago, Nick Bys said:

I do have voltage at the sender and at the tacho albeit very little 0.23v at tickover 0.65 at guessing 2500rpm actual engine speed. This displays 300rpm and 700rpm respectively on the tacho gauge. 
 

unfortunately I don’t have Hz on my multi-meter, could borrow one to check the output tho. 
 

Nick 

 

Thanks.

 

That looks very like a generator sender but I can't see exactly where on the engine it is or what it might be driven from. If i am correct then a Hz meter might not do any good, but if the sender produces AC then it would. You need the meter set to AC volts, not DC in all probability. Trying to measurement AC voltage with a DC meter will give all sorts of odd and probably low voltages because each half wave tends to cacel the last one out. However the sampling rate of a digital meter will also screw the readings. See what you get when using the AC volts.

 

If I am correct it is probably just a spinning permanent magnet and a stationary generating coil, so not much to go wrong. The last time I saw one of those was on a Jaguar gearbox for the speedo. You may find one from vintage tractor spares outfit.

 

Now I fear that I may be complicating things. I have seen a mechanical rev counter drive fitted to BMC 1.5s that look like that so the date and that drive makes me wonder if you really have a BMC 1.5. Where is the injector pump mounted? Stuck out the side of the engine where a distributor would be on a petrol engine or tucked under the alternator parallel with the engine block?

 

I suspect if you undo the large nut immediately under the tin can the sender will lift off. you could then inspect the drive.

 

 

 

[Nick Bys]

21 minutes ago, Tony Brooks said:

 

Thanks.

 

That looks very like a generator sender but I can't see exactly where on the engine it is or what it might be driven from. If i am correct then a Hz meter might not do any good, but if the sender produces AC then it would. You need the meter set to AC volts, not DC in all probability. Trying to measurement AC voltage with a DC meter will give all sorts of odd and probably low voltages because each half wave tends to cacel the last one out. However the sampling rate of a digital meter will also screw the readings. See what you get when using the AC volts.

 

If I am correct it is probably just a spinning permanent magnet and a stationary generating coil, so not much to go wrong. The last time I saw one of those was on a Jaguar gearbox for the speedo. You may find one from vintage tractor spares outfit.

 

Now I fear that I may be complicating things. I have seen a mechanical rev counter drive fitted to BMC 1.5s that look like that so the date and that drive makes me wonder if you really have a BMC 1.5. Where is the injector pump mounted? Stuck out the side of the engine where a distributor would be on a petrol engine or tucked under the alternator parallel with the engine block?

 

I suspect if you undo the large nut immediately under the tin can the sender will lift off. you could then inspect the drive.

 

 

 

The sender is bolted just behind the bell housing, pump is located under the alternator.

Pics attached 

sender pic is upside down sorry 

Edited January 26, 2022 by Nick Bys

[Tony Brooks]

Thanks. Its a1.8 but I have never seen a tacho drive there. It's driven off the camshaft.

 

It seems VDO  supply similar senders but at a minimum of $120 + currency conversion + carriage + duty & VAT a new alternator driven one is likely to be cheaper. Also Farier seem to imply their revcounters can be generator driven and ASAP Supplies stock those gauges.  Calcutt Boats specialise in BMC 1.5s and 1.8s so they may have a lead.

[Nick Bys]

49 minutes ago, Tony Brooks said:

Thanks. Its a1.8 but I have never seen a tacho drive there. It's driven off the camshaft.

 

It seems VDO  supply similar senders but at a minimum of $120 + currency conversion + carriage + duty & VAT a new alternator driven one is likely to be cheaper. Also Farier seem to imply their revcounters can be generator driven and ASAP Supplies stock those gauges.  Calcutt Boats specialise in BMC 1.5s and 1.8s so they may have a lead.

Thanks for all of your help, I’ll continue my investigations and report back with my findings. 
 

Nick

[RLWP]

Buying a modern tacho to read off the W terminal of the alternator may be a simpler answer

 

Richard

 

 

[Nick Bys]

13 minutes ago, RLWP said:

Buying a modern tacho to read off the W terminal of the alternator may be a simpler answer

 

Richard

 

 

It’s looking highly likely this will be the route I’m forced to take. The gauges are all original and matching, I was hopeful I may be able to keep them that way. 

N

[Jen-in-Wellies]

37 minutes ago, Nick Bys said:

It’s looking highly likely this will be the route I’m forced to take. The gauges are all original and matching, I was hopeful I may be able to keep them that way. 

N

New innards in the old gauge may be possible. Try the classic car fraternity. Help you keep the matching look of the old gauge, but at a cost.