BMC 1.5 diesel cylinder head bolt size

[GBW]

What size are they?  I believe 7/16" UNF but others say 3/8" UNF.

There are two "thicknesses" two carry the filter assy.

 

[Tony Brooks]

I had a feeling they have a coarse thread in the block, so take care. I am not going to swear to that, but it was common practice.

 

I seem to recall the socket size is 5/8 AF for all the true head studs, so probably 7/16 UNF (but you can never be sure with BMC).

 

The rocker post screws that screw into the head are, I think, 5/16, but again I suspect a different thread on each end.

 

As far as I know, the filter bracket fits on the normal head studs, so the same diameter as the others.

 

This site may help you get the stud size from spanner size:

 

https://www.bolts.co.uk/guides-and-tips/nuts-and-bolts/imperial-and-metric-spanner-sizes/

[GBW]

Thanks Tony.

I buy my bits from MG Owner Club as the service is slick (and the prices low) but the spares website is a little light on the illustrations (and they had a website problem yesterday).

I have mislaid two head bolt nuts.  I ordered what I thought were the correct replacements but received 3/8" UNF and thick washers (listed as 5/16" but actually 3/8".

Two of the head nuts are extra height, through threaded and the filter bracket bolts on top.

The OD of the bolt measures 0.437 which is 7/16".

Thanks.

[Tony Brooks]

4 minutes ago, GBW said:

Two of the head nuts are extra height, through threaded and the filter bracket bolts on top.

 

So height/length, not thickness.

 

I think that is the mariniser's adaption. I can't recall any longer ones on the Newage/Tempest marinisations. I don't recall needing a deep socket for the bracket nuts. The brackets from various marinisers did vary.

Edited April 12 by Tony Brooks

[GBW]

The fuel filter is fitted on the rear end of the engine (also the case on my existing soon-to-be-replaced fitted engine).

The bracket has two holes and the extra thick nuts to raise the filter(s) to clear the engine block.

I think you are correct about the thread difference.  It is certainly the case with other head threads.  I read somewhere that a coarse thread, UNC (but in my recall Whit) is a stronger solution in cast iron.

Thanks for the steer to spanner sizes.  The site confirms my feeling.

I found a 11/16" ring spanner to fabricate a "joggled" spanner for the nuts buried under the rocker shaft.  (The first attempt with an open ended spanner failed due to the high torsion involved).

[Tony Brooks]

43 minutes ago, GBW said:

I found a 11/16" ring spanner to fabricate a "joggled" spanner for the nuts buried under the rocker shaft.

 

So how do you intend to torque those nuts up? You either need a crows foot spanner/socket or fit the rocker shaft, tighten the thinner studs, and the draw shaft (assuming enough room) leaving the pedestals in place, torque up the head and then refit the shaft. That becomes a bit f a jigsaw with the washers, springs and rockers.

[GBW]

The ring spanner is welded to a Ø10mm bar at right angles to the spanner shank.  The bar length is ~60mm.  The other end is welded to another socket end, Ø17mm on the end of the ring remains of the first attempt spanner, such that the two socket ends are coaxial.  The top ring is welded to a scrap 1/2" square drive socket.

They do say a picture is worth a thousand words - I'll work on it!

The manual recommends a torque setting of 70 N/m which is pretty heavy.

I was wrong about the studs - they are 7/16" UNF both ends.

 

Don't know how to edit but this is similar;-

https://www.ebay.co.uk/itm/165316833785?_trkparms=amclksrc%3DITM%26aid%3D1110013%26algo%3DHOMESPLICE.SIMRXI%26ao%3D1%26asc%3D260662%2C259211%26meid%3Dc0e464d8d4714bf08a2bdf222dc6272c%26pid%3D101196%26rk%3D2%26rkt%3D10%26sd%3D282637444535%26itm%3D165316833785%26pmt%3D1%26noa%3D0%26pg%3D4429486%26algv%3DPromotedRVIPbooster%26brand%3DNeilsen&_trksid=p4429486.c101196.m2219&itmprp=cksum%3A165316833785c0e464d8d4714bf08a2bdf222dc6272c|enc%3AAQAJAAAA8CwDxH%2FaslyJlxG5OwCzDVsHsIpNfYFGjhmSnkcbenJ%2B6nDWuSVkbkB4hA4oh2CvlddofizzQXlReWwdqZopWRNfHi2CePero5V1lLpX8dLNwpRfjv%2FRu860dkqXFbCLUwx6Mpanz%2BIuLjAWVonEwNqdCaUCxZy%2BHdv67PxfgwaB8aEvfnMA2hdvVhE%2FEgE1ekCvN5CRzFcvGkiUpRCITuwn2ACJEOwFqoeI7EcgxzTojt4nVyatZ9t1vYsMy1dDNrY4cO817dD5h2eYn2RfQaaoNj8gArD2PcXgwmxzeNX4GUJfrlaNLHpMLMkIgYhddQ%3D%3D|ampid%3APL_CLK|clp%3A4429486&epid=12022202515&itmmeta=01HV9DEDG8WKZJZCQVABE82MRE

[Tony Brooks]

Very pleased to hear you have a tool for those nuts, I fear that nowadays many do not torque them up.

[GBW]

I have juat heard from MG Owners Club.  The MGA and B head studs are 3/8" UNF but the MGC are 7/16".  I have placed an order.

Thanks for your help.

[Tracy D'arth]

2 hours ago, GBW said:

The ring spanner is welded to a Ø10mm bar at right angles to the spanner shank.  The bar length is ~60mm.  The other end is welded to another socket end, Ø17mm on the end of the ring remains of the first attempt spanner, such that the two socket ends are coaxial.  The top ring is welded to a scrap 1/2" square drive socket.

They do say a picture is worth a thousand words - I'll work on it!

The manual recommends a torque setting of 70 N/m which is pretty heavy.

I was wrong about the studs - they are 7/16" UNF both ends.

 

Don't know how to edit but this is similar;-

https://www.ebay.co.uk/itm/165316833785?_trkparms=amclksrc%3DITM%26aid%3D1110013%26algo%3DHOMESPLICE.SIMRXI%26ao%3D1%26asc%3D260662%2C259211%26meid%3Dc0e464d8d4714bf08a2bdf222dc6272c%26pid%3D101196%26rk%3D2%26rkt%3D10%26sd%3D282637444535%26itm%3D165316833785%26pmt%3D1%26noa%3D0%26pg%3D4429486%26algv%3DPromotedRVIPbooster%26brand%3DNeilsen&_trksid=p4429486.c101196.m2219&itmprp=cksum%3A165316833785c0e464d8d4714bf08a2bdf222dc6272c|enc%3AAQAJAAAA8CwDxH%2FaslyJlxG5OwCzDVsHsIpNfYFGjhmSnkcbenJ%2B6nDWuSVkbkB4hA4oh2CvlddofizzQXlReWwdqZopWRNfHi2CePero5V1lLpX8dLNwpRfjv%2FRu860dkqXFbCLUwx6Mpanz%2BIuLjAWVonEwNqdCaUCxZy%2BHdv67PxfgwaB8aEvfnMA2hdvVhE%2FEgE1ekCvN5CRzFcvGkiUpRCITuwn2ACJEOwFqoeI7EcgxzTojt4nVyatZ9t1vYsMy1dDNrY4cO817dD5h2eYn2RfQaaoNj8gArD2PcXgwmxzeNX4GUJfrlaNLHpMLMkIgYhddQ%3D%3D|ampid%3APL_CLK|clp%3A4429486&epid=12022202515&itmmeta=01HV9DEDG8WKZJZCQVABE82MRE

That is similar to the official special tool that BMC used to sell.

I use a ring crowfoot 1/2" drive.

[GBW]

Despite an extended search, I could not find an original hence my own attempt.

[LEO]

I used to have one of those 'special' spanners shown in the illustration, purchased it from 'Snap On', made life a lot easier when I had a 1.5. Good luck, I recall the nuts were 5/8 AF........

[Tracy D'arth]

2 minutes ago, LEO said:

I used to have one of those 'special' spanners shown in the illustration, purchased it from 'Snap On', made life a lot easier when I had a 1.5. Good luck, I recall the nuts were 5/8 AF........

I thought they were 11/16" AF nuts,but time has passed......

Admirable bit of tool making, needs must etc.

[GBW]

11/16" or 17mm "modified" with a bit of effort!

The first attempt used an open ended spanner on the nut.  It couldn't cope with the torque.

[Tracy D'arth]

1 hour ago, GBW said:

11/16" or 17mm "modified" with a bit of effort!

The first attempt used an open ended spanner on the nut.  It couldn't cope with the torque.

I thought so.  I think the A series engines were 5/8".

I had an open end crowfoot, not strong enough.  I hope your welding is up to it!