First Time Engine Rebuild

[Declan_Burns]

When I did the 940 head I used a vernier gauge to measure the depth of the valve from the head surface.[frame][/frame]
I then used a valve seat cutter to sink the valve and then a final grind with coarse and fine grinding paste.[frame][/frame]
No issues with the head gasket and has been running fine for the last six years.

Regards
Declan

[edd_barker]

Got to love a good debate! Thanks for all the replies, interesting that there is no one 'right' way to do anything it seems.

Thanks for those pictures Declan, I had managed to track them down on the original post on a mini forum, that makes it very clear the sort of caliper I need to buy to measure my current clearance.

BMC, I'd be interested to hear more detail about exposing the top ring to excessive heat, what problems this might cause, and how you learnt that this was the case? I haven't read my Vizard in a while, so I will go back and see what his 2 cents are regarding block pocketing.

The block is already completely stripped down, for dipping etc. It's a spare engine. I started this project for the enjoyment and challenge of rebuilding an engine, not because I needed it. Whilst I don't want to spend a lot of money, I don't consider this to be a budget rebuild, and I would like the engine to be 'as new' when I fit it into the car, preferably better than the original!

Regarding sorting the rest of the car, the chassis and underside are available for eating ones dinner off, its the sh*t paint job the previous owner did that needs removing and respraying (snore). Suspension is standard, all polybushed over the last 3 years. I replaced all the brake components last year, and fitted a servo! Shock horror...I much prefer it for brake feel, and I am definitely not lacking in the leg strength department. Tyres are new and fitted to wider LP936 wheels, so it stops pretty well.

As soon as I hear back from the engineers I will post what they say, and then let you all know how the engine progresses along, I'm sure there will be many more questions!

Thanks,

Edd

[bmcecosse]

It's obvious - if you grind a 40 thou pocket in the cylinder wall - you can SEE the top ring! I did this 50 years ago now - it's not a new thing - when I fitted a Cooper S head to a 998 engine, The ring could be seen at TDC. It was a short run 'race' engine, so was acceptable then - but it's far far easier to just sink the exhaust valves. No-one has come on to 'defend' the pocket idea - just your 'engineers' who don't understand how a countersink works !! Good luck with them - we've given you our collective advice on how the job can be done very easily and without any problems.

[Declan_Burns]

Edd,
Here's a cheap way of measuring the valve depth-same principle as shown above but a lot cheaper.
http://www.ebay.co.uk/itm/Digital-Tyre- ... SwGotWtgAL
It can also be adapted for a pillar drill or fitted to a lathe tail stock.
Regards
Declan

[amgrave]

or, get yourself down to an Aldi's branch near you they have got Digital Callipers @ £7.99 on sale from the 7th Feb.

[philthehill]

Well I will defend the pocketed small bore block for what it is worth.
As I have said above it is a well tried and tested modification and Vizard refers to it with diagram in his Book 'How to Modify Your Mini' ISBN 0-86343 0414 (U.K.) page 63.
Only if you are greedy and take too much out of the block will you get problems.
Edd - it is up to you how you tackle the valve to block fouling but I know which way I would resolve it.
Phil

[edd_barker]

Not sure I was expecting such a heated debate!

Thanks Declan and Mr. Amgrave for the advice on measuring, I will get myself down to Aldi this afternoon, the tyre gauge looks really handy as well, even just for the van tyres!

BMC, thanks for your advice and input, I fear that what may be obvious to you with 50 years of A series engineering experience is not so obvious to someone who has only had a moggie thou' for 4 years, and seen a piston ring once in their life (4 days ago when I took them off). So far I have had advice from 3 forum members advocating the pocketing of the block, and then advice from yourself and others regarding sinking the exhaust valves. I am trying to weigh up what is best by listening to as many opinions and reading as much as possible, hence my persistence with querying both options.

Hopefully I will be getting an exchange, recon head, with unleaded seats and enough clearance from Minor Millennium. I just have to get myself to Manchester with a big rucksack in the near future.

Thanks again all, I look forward to asking more questions!

Edd

*EDIT* - Thanks Phil! I think using terms like 'defend' is only going heat up this debate even more! I suggest we settle with a fist fight at the next AGM. I don't have that book, just the 'yellow bible' modifying the A series, is the relevant chapter/page in that book also? Look forward to more passionate opinions on the topic

[philthehill]

Edd
I have the Vizard book 'Tuning BLs A Series Engine. I have not had chance to dig into the subject of fitting 940 heads to small bore blocks as there is a lot of information contained in his book but sometimes you have to look in areas you may not expect to find the information you want.
Sometimes you also have to read his books in conjunction to extract the full information.
Here is a post I put up regarding publications relating to tuning and improving the 'A' Series and associated works which you may find interesting.

http://www.mmoc.org.uk/viewtopic.php?f=4&t=61780

The one subject that has not been touched upon and relates to sinking the valve into the head is the valve rocker geometry. If you want to get the very best out of the engine you have to maintain valve rocker geometry. Sinking the valve even by a small amount puts that geometry out. It is no different as to when you skim the head to improve the compression and then have to pack underneath the rocker shaft pedestals the equivalent amount of metal removed to maintain the geometry.
Incorrect valve rocker geometry can lead to valve stem and valve guide wear.
There is a lot more to engine building than just putting it together.
Phil

[bmcecosse]

There is no 'right' way to do the job - however you look at it - it's a 'bodge', fitting a head from a different engine - but a very economic bodge, that works very well and releases a good deal of extra power from a 1098 engine at little expense. You do not need 'unleaded' seats for the exhaust - you do ideally want a well worn 940 head - small valve version - fit new guides and measure the exhaust valve head depth. You may not need to do anything at all! However it seems to me the whole thing is a lot of worry for you - so perhaps you would be better to just find a 12G295 head (ex MG 1100 etc), skim it 60 thou (if not already skimmed) and bolt it straight on with no mods to block or valve sinking required. It won't give quite as much power - but it will be better than standard, and save you having sleepless nights about water leaks ! Phil is of course right about the valve geometry - but the effect is minimal as long as you don't sink more than 40 thou, and hasn't affected my engine in the last 9 years or so with the 940 head fitted. Of course - if you do fit a skimmed 295 head - you still have to 'worry' about the valve geometry.....

[les]

Don't blame the man for worrying about getting things right, I've found those that don't worry are the problem!

[panky]

That'll be me then

[edd_barker]

Guys help, I went to Aldi and bought a measuring caliper, but I can't make any sense of it?!

Whatever the depth I try and get it to measure, it always shows the same thing, but in F?? What kind of measurement is this??

Any help would be great, how many F should my valve gaps be?? is 72.1F enough clearance?

Thanks

Edd...

[frame][/frame]

[panky]

Erm, that looks like a digital thermometer

[panky]

Nice warm garage you've got there

[bmcecosse]

It's a kitchen thermometer - little use in an engine rebuild ! I'm assuming you are 'joking' with us here.....
The problem of course with pocketing a 'good' block' is that if for some reason you run into a problem with water leaks or gasket blowing (I don't know why - but you may be unlucky..) there's no way back to using a standard head. If you keep the modifications in the head- then you can put the engine back to standard very easily.

[edd_barker]

Haha, I must admit I made myself laugh with that one!

The calipers from Aldi seem decent, I haven't measured anything precision engineered yet, but construction/overall quality seems good and they return to zero when closed each time. They have a depth gauge on the end.

I think the most likely option is I will go for a 940 with the valves already sunk, from Minor Millennium, their recon exchange price is good, I just have to go via Manchester to pick it up.

The engineers will dip the block, fit new cam bearings, rebore, skim, if its only £40 I'll have that waterway plugged so you all won't be worrying about my sleep patterns...then crank ground and new pistons/bearings all round. Should be a proper reconditioned engine.

Do I need to consider cam timing much? I'm aware I can't go for a higher lift cam, I've been reading about timing variation with the dots on the cogs not being enough to accurately base cam timing on, worth getting the Kent timing disc? It looks quite straightforward, if the engine is already out.

Thanks,

Edd

PS - If you don't have a kitchen thermometer, get one. Never serve dry roast chicken again!

[bmcecosse]

Sounds like a plan. I've checked cam timing before with the 'equal overlap lift at TDC' method and never found anything wrong with the dot to dot method. It's not easy to do accurate cam timing - you need a dial gauge and it's fiddly to get any really accurate readings. With a standard cam and new timing gears - it will be fine.

[philthehill]

To bring the rocker geometry somewhat back into line a rocker post locking plate (Pt No: 2A259) (or the spacer below from Mini Spares) can be inserted under each rocker shaft pillar.
http://www.minispares.com/product/Class ... .aspx|Back to search

Two other things that need to be considered when fitting a 940 head to a small bore block is the length of the pushrods used and the length of the tappet adjustment screws.
Note: BMC used to sell special tappet adjusting screws to accommodate the change over.
If using the original rocker assy and decide to upgrade the valve springs make sure that the rocker adjusting screws are not hollow. This was done on early 'A' Series engines to allow oil from the rocker shaft to reach the adjuster end of the rocker and eventually the cam follower. The hollow ones are not suitable for stronger springs.
Also make sure that if you have the tapped No: 1 rocker shaft pillar you will have to move the tapped pillar to pillar position No: 2 and drill the new No: 1 pillar to allow oil to pass from the head to the rocker shaft The way oil is delivered to the rocker shaft is different on the 940 head. You will also require a new shaft to suit the new pillar arrangement. The details are in the Vizard book.
Phil

[Mark Wilson]

Nice one! At least you know exactly how heated the debate is getting....

[philthehill]

So long as you do not use a reground camshaft and fit a new camshaft from a reputable supplier there is no requirement to time the cam just go for dot to dot.
To accurately set the cam timing you will need the timing disc & two dial gauges . One on the top of the piston to determine TDC; and one for the cam follower to determine lift at the manufactures specified degrees.
I have a Kent Cams vernier adjustment duplex set up fitted to my Minor engine and the only way you can set the initial cam timing is to use the two dial gauges and the timing disc.
Phil