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Bmc 1.5 Cylinder Head Rebuild


RLWP

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This was a recent job, and I would rather not reveal who the boat belongs to so as to avoid embarrassment.

 

My heart sank when I took the rocker cover off and found this. This is the valve clearance as found:

 

tappet-clearance.jpg?i=722697901

 

The clearance here should be around 0.015", this must be four or five times this. Notice how 'dry' the rockers are.

 

The pushrod end looked pretty nasty too:

 

rocker.jpg?i=1988861995

 

Several of the adjusting screws had been running completely dry, producing the characteristic red frettage powder:

 

pushrod-1.jpg?i=1946239599

 

This looks like a classic oil feed problem. There could be a variety of causes for this, starting with wrongly assembled rockers. One of the pillars has an oil feed in it to line up with the feed in the head. You can see the hole between the studs at the bottom:

 

oil-feed-1.jpg?i=315765862

 

The right pillar was in the right place, so next stop is at the head gasket

 

Bingo!:

 

oil-feed-2.jpg?i=1858528716

 

This isn't right, the oil feed to the head should be here. Sure enough, under the head gasket was:

 

oil-feed-4.jpg?i=1754237425

 

The oil feed! What's wrong is that the gasket is on upside down, the hole in the gasket being at the wrong end:

 

oil-feed-3.jpg

 

And it was bloody glued on as well!!!

 

Anyway, net result was that no oil got to the rockers, so the bearings wore out.

 

rocker-1.jpg?i=1362885902

 

rocker-2.jpg?i=1241051682

 

Naturally the shaft was completely wrecked too. Fortunately, the bushes, rocker shaft and valve guides are the same as for a BMC 1.8 in an MGB - meaning car prices rather than boat prices!

 

This is a new bush:

 

rocker-3.jpg?i=353548904

 

They are supplied undersize and have to be reamed to size when installed. I took some of the meat out first in the lathe:

 

rocker-4.jpg?i=657264603

 

There are two oil feeds in the rocker. One sprays oil about to lubricate the valves and springs, the other feeds to the top of the pushrods. That feed has a plug in the end:

 

rocker-5.jpg?i=436652358

 

Which had to be removed:

 

rocker-6.jpg?i=369541681

 

so that a hole could be drilled through the bush:

 

rocker-7.jpg?i=821724230

 

before finally reaming to size:

 

rocker-8.jpg?i=643277002

 

I made up and fitted some brass plugs to finish the oilways, sorry no photo.

 

Richard

 

I can't get any more photos into this posting

Edited by RLWP
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Meanwhile, at the other end of the rockers:

 

rocker-9.jpg?i=1988766124

 

This is where the ends of the valves have worn into the pads on the rockers. This means that you can't set the clearance with a feeler gauge, and - worse - the 'cup' grabs hold of the end of the valve and pulls it sideways, damaging the valve guides.

 

I fixed this the old fashioned way - by hand with an oilstone:

 

rocker-10.jpg?i=977018349

 

All of the valve guides were wrecked, so they were replaced. For reference, they are all 'long' guides, the same as the MGB exhaust valves:

 

valve-guides-1.jpg?i=514416966

 

These guides have to be reamed to size once installed:

 

valve-guides-2.jpg?i=664861075

 

and because the guides may no longer be coaxial with the seats, they had to be recut as well:

 

valve-seats.jpg?i=1242337329

 

Everything got bunged in my new toy,and we are ready to rebuild:

 

cleaner.jpg?i=593304782

 

Richard

Edited by RLWP
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Yes Ray, I'll slip you into a box under the bench

 

I forgot to say, I had the head lightly skimmed:

 

skimmed-head.jpg?i=1127002257

 

Not much to add now. The head gasket the RIGHT WAY AROUND:

 

head-gasket.jpg?i=1253420735

 

Next, the famous BMC head nut problem. There are three like this:

 

head-bolt-1.jpg?i=1896113471

 

OK when the rocker shaft is off, but not so when it is in place:

 

head-bolt-2.jpg?i=1428645250

 

Right underneath the shaft, so you can't get a socket and torque wrench onto it.

 

The solution is a crow's foot spanner on a 3/8" extension:

 

head-bolt-4.jpg?i=2139998808

 

And, all together again - much quieter!:

 

top-end.jpg?i=445089726

 

I even got away with chucking my phone in the cut:

 

wet-phone.jpg

 

Richard

Edited by RLWP
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Did a similar rebuild on an MGB head with the 2708 casting - 43mm inlets. Went to the trouble of adding 3 angle unleaded valve seats, necked the valves, opened up the ports, matched the ports to the manifolds, equalised the combustion chambers etc. It's sat in the garage ever since and for the last 15 years not moved a wheel!

 

There's a special tuning mod that opens up the diameter of the water feed to the head that's meant to improve flow to the head.

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Nice work Richard, I might have to get in touch soon about my challenging engine.

Have you got a bead roller by any chance? I have some 32mm stainless elbows that need, err... ...beads rolling

 

Robert

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Hmmmm no embarrasment Richard .... it was my head that got rebuilt ..... I am extremely grateful and would thoroughly recommend Richard and Primrose Engineering to any one here who has engine problems .... his work was meticulous, he is a great guy and my head came back spanking clean and painted a lovely shade of green wub.png

 

(mind you, I have not had the invoice yet wink.png )

 

Some of you will have been following the recent overheating shenanigans on previous threads that myself, and Bengt, had been struggling with following the earlier "screw incident" .... my head had been off earlier in the year and put back on by a well respected and time served spannerman, but with the gasket on upside down. People make mistakes, and in mitigation, it was sub zero and blowing a blizzard at the time.

 

Whether we have cured the overheating or not will be revealed hopefully today when I finally get to leave the fleshpots of Brownhills ..... but good job done Richard and great pics

clapping.gif


and glad the phone survived its swim in the curly wyrley biggrin.png

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Thoroughly enjoy these threads Richard.

 

It is the modern equivalent of reading a Haynes manual. I get to look at the photo's and see the progress without having to get grease under my fingernails (and on this occasion without having to foot the bill!)

 

It is a lovely feeling when you find something that is causing a problem. I bet you are really looking forward to trying it out now Bunny

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{snip}

 

People make mistakes, and in mitigation, it was sub zero and blowing a blizzard at the time.

 

{snip}

 

They do indeed, I do too. You'll remember I was more annoyed by the sealant than the gasket being upside down :). Indeed, some BMC gaskets are made with two oil holes to protect the unfortunate mechanic

 

Richard

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Very nice work and photos Richard!

 

I'd like to think that had I been the previous bod who put the head on with the gasket upside down, I'd have noticed the absence of oil oozing from the rocker bearings on initial running the engine and adjusting the tappets.

 

Maybe he was just pleased not to get splattered with the tiny spots of oil that spray everywhere prior to replacing the rocker box, or maybe he was just too cold. I've never done it in a freezing blizzard either!

 

MtB

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It seems there's now a very Happy Bunny.

 

You would think so ..... BUT despite Richard's careful work, that was clearly in need of doing, and a head restored to lovely condition .....

my overheating problem has not been cured ........frusty.gif

 

so everything flushed and bled, head pressure tested etc etc etc ...... (this has to be said in the style of Yul Bryner in "The King and I") ......

 

she still starts to heave and belch as soon as she is asked to do more than 1200 rpm, and comes to a rolling boil at above 1500 rpm

 

she never did this before the "screw incident" earlier this year, when the head came off for first time (since I have had her) .... and it has got worse as time has gone on.

 

Any suggestions ?? unsure.png

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An obstruction to the water somewhere. Is it possible that when the first lot of work was done some foreign body or detritus found it's way into the water jacket and is preventing the water circulating. as fast as it should.

 

It is a tricky one because it could have moved it's way around the water system from where it first entered and lodged somewhere where it just stops it flowing fully.

 

I feel daft saying this as I know Richard will have already thought this through but have you tried flushing the water system and have you checked the water pump?

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I feel daft saying this as I know Richard will have already thought this through but have you tried flushing the water system and have you checked the water pump?

 

Oh yes. I got wet!

 

And, I'm still on the case smile.png

 

One of the problems (I think) is that, although appearing simple, this system is actually tricky to bleed properly.

 

Richard

Edited by RLWP
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Is there enough of us with overheating BMCs to create a club?

 

As yours was ok before the screw incident I'd suspect getting it flushed and and all the air bled out will fix it.

 

Good Luck

 

Rob

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I suffered with an overheating BMC 1.5 diesel for many years as most of my boating is on the river Nene . Cured it in the end by taking it to Charlie Fox at March and having external cooling pipes welded on as he fitted to his boats . This does away with the skin cooling tank that was never up to it . Best money I ever spent as engine has never overheated since that day plus the cooling system is no longer pressurised with just an open header tank .

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Is there enough of us with overheating BMCs to create a club?

 

As yours was ok before the screw incident I'd suspect getting it flushed and and all the air bled out will fix it.

 

Good Luck

 

Rob

 

Hmmm what is the collective noun for people with hot and bovvered BMC engines?

 

A blather of BMCs ..... A swelter of BMCs ..... A simmer of BMCs ?

 

Many innocent people have now been liberally soaked during numerous attempts to flush and bleed the cooling system .....

 

It is good to know I am not alone ..... smile.png

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Nice work and good pics but do I take it I should reconsider buying a boat with a BMC engine? Do they all overheat and what are the good points?

 

hmmm a deafening silence on the good points ..... despite this recent problem .... mine is a much loved and trusty reliable old friend now .... and you can get most parts / spares / filters etc in a motorfactors rather than having to pay chandlery prices

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