Head gasket gone. Again + again +again + again.

[bigginger]

Ins't it just a question of spreading blue over the glass (on the assumption that it's flat, so it had better be new) and moving the head across it? Any places that don't pick up blue are therefore warped. That's my understanding of it, anyway.

[Dominic]

Ian
The plate glass method is as follows:
Plate glass, being flat, (assuming it's of a reasonable thickness) is coated with a very fine film of marking blue. This is then placed on the surface to be checked, and moved around slightly. Any high spots on the head or block will pick up traces of blue which can then be removed by careful filing, or better still, scraping. (Scraping is far more selective than filing, which can remove too much metal from the wrong places! It is however a slower process.) The above is repeated until an even mottling of blue covers the entire surface. It takes ages! Have fun!

[Onne]

It must be national blow your gasket week this week. Mine has blow between three and four, the fourth not having much of a compression

[chrisd87]

Perhaps that's the reason she'd only do 68mph, Onne?

[Onne]

might very well be, but last time I checked there were more psi's hanging around in nr 4

[Kevin]

Ian, Dominic`s method description is great, however if you are not used to hand tools I would not try and attempt to remove any high spots by either method, use of a file can be very problematic and you need to have planty of practice with a scraper to be able to use one correctly preferably with someone showing you how to use it.
What it does do however in using the engineers blue is show whether the head is flat or not and if not I would take it to a workshop where they can put it on a surface grinder and grind it true once again which is the method I personally would opt for and as I use to be a toolmaker this is far quicker than trying to use a scraper (I personally would never use a file on a cylinder head).
I also think that Dominic must have untold patience to tackle a job like this using a scraper as it sounds like he has done a few the hard way.

[Dominic]

Kevin
I haven't (yet) scraped a block or head, but years ago when a student of the art of violin making, I needed to flatten my woodworking planes via this method. The longest was 24", the shortest about 6". It took ages and ages........ and ages!

[Kevin]

Yes Dominic the things they make you do as a student or apprentice just to show you how it should be done in case there is not a machine available, my first experience with a scraper was with the curved type and I had to make a 6" bearing fit into a cradle and once finished I asked how long does it take an experienced engineer the reply was dont be silly its done on a line borer as its far quicker

[Dominic]

A very valuable part of my education all the same! I used a curved scraper, slightly radiused, rather like a giant screwdriver if my memory serves me correct! I made one up recently from an old file, invaluable for de-coking the piston tops, and removing old gaskets.

[wanderinstar]

Well thanks for that. How thick a piece of glass would you need and could you just go into a glass merchant and buy a piece of say 9" x24" plate glass.
Ian.

[Dominic]

Ian, it would only need to be a few inches larger in both dimensions than the size of the head and block face. As for thickness, the thicker the better as the actress said to the bishop! seriously though, I'd guess that 3/8" would be thick enough, 1/2" would be even more stable. Ring around the glass merchants for availability and prices?

[ian-s]

I would only use the glass to show if the block is flat or not, I doubt that the plate glass and scraper method is really viable to correct it. It is bound to show it is touching on only a few areas at first and gives you no idea how many thous out it is. I would think the time taken to scrape a block flat would be less than the time taken to take the motor out, strip it and get it machined flat . Whilst it is a valid method if no machinery is avalilable it will take days of hard manual work.

[bmcecosse]

Ian - a steel rule with a bright light behind it will tell you all you need to know ! It's unlikely any used head or block will be perfectly flat - there's a degree of acceptability. My 1098 blew it's head gasket 6 years ago - i changed it at the side of the road (had to walk a mile into town to buy a gasket (£3 - so I bought 2 !) and a mile back of course - so now I always carry a spare gasket!) using only hand spanners - and it was still in perfect condition when I took the head off earlier this year to fit the 12g940 head.

[Kevin]

Ian as you are unsure of most of these methods, things like scrapers etc do need quite a bit of engineering skill to be used successfully so to be honest I dont think you should use these methods and to some extent the same with the engineers blue method as well.
BMc`s method with a good quality steel rule is probably the easiest method but it does need to be a good quality engineers steel rule of about 12" with an undamaged edge otherwise it will not be accurate test, and dont forget to check the stud holes in the block as mentioned by Willie.
One thing I have to ask how did you determine that the replacement head was indeed flat ?

[bmcecosse]

Yesterday while changing the engine in my Mini - I decided to check the block (1360 so big bores) for flatness before fitting the head. The area around each stud hole seemed slightly domed - so a newish flat file was employed - held flat down to the block, and kept away from the bore edges - and this did a good job quite quickly of levelling off the stud area. I then put a very slight countersink on the threaded holes.