bmcecosse wrote:They are water ways - not oil ways - the single oil passage is perfect. It's never been a problem for me - certainly don't modify the gasket by cutting in to the rings! Smear of grease and clamp it down - torque to 44 ft lbf in easy stages. Retorque after the first heat cycle - and then reset the valve gaps to 12 thou inlet and 15 thou exhaust. Did you put 32 thou shims (washers!) under the exhaust valve springs to compensate for the 'sinking' ?
bmcecosse wrote:They are water ways - not oil ways - the single oil passage is perfect. It's never been a problem for me - certainly don't modify the gasket by cutting in to the rings! Smear of grease and clamp it down - torque to 44 ft lbf in easy stages. Retorque after the first heat cycle - and then reset the valve gaps to 12 thou inlet and 15 thou exhaust. Did you put 32 thou shims (washers!) under the exhaust valve springs to compensate for the 'sinking' ?
Both surfaces should be "clean and grease free" I clean the head and block with a solvent cleaner so there squeaky clean.
Grease doesn't do any sealing action on gaskets EG waterpump it's used purley to "stick" it in place while the assembly is clamped up.
particularly with copper laminated head gaskets, grease was the norm to help it move as it is being compressed. I always grease those but don't bother with composite caskets.
BMCE, of course it alters the valve timing as the rocker geometry is altered, I said nit picking, but it is true. The ideal geometry is for the rocker to be horizontal at half lift. Greatest valve acceleration is around that position and as the angle increases the acceleration drops off and the amount of lift per degree of rocker angle also drop off. So at opening the valve will lift slower retarded) than one that isn't. As for valve shrouding, it's not just in the throat but in the chamber as the valve has to lift to pre sink height before it starts flowing properly. Sinking valves improves power, never.
Ok -well - I agree to an extent - there could be a TINY change in the valve LIFT since the rocker may not be operating ideally - but the TIMING is only controlled by the shape of the cam lobe. I think KCs theory was that the reduced throat length helped the flow, and as I said - the valve should be unmasked with a small grind stone after it has been 'sunk' The vastly greater area exposed by the larger valves in the 940 head comfortably lifts the flow well beyond any standard Minor head. Remember -this is flow OUT of the chamber - the gas is at relatively high pressure when the valve opens, and so isn't so bothered by any masking around the valve as it would be on the inlet side.
I had the restricting copper rings around the waterways cut out from the gasket at the engine shop who did all the work on my cylinder head, and they were sure the slight overlap would not cause any problems. I'll keep you posted. I am now eagerly waiting for the early MGB thermostat housing to finish off this top end rebuild.[frame][/frame][frame][/frame][frame][/frame]
having just had a reminder about a new post on this topic, also reminded me that I hadn't replied to this point:-
"Remember -this is flow OUT of the chamber - the gas is at relatively high pressure when the valve opens, and so isn't so bothered by any masking around the valve as it would be on the inlet side."
What is important that although it is high pressure, the volume within the cylinder is very much more than the intake, and that any restriction in evacuating the cylinder affects the capacity for the cylinder to fill on the intake stroke, i.e it affects scavenging.
Alec - Of course it does - it's obviously not absolutely ideal - but it's perfectly possible to 'unpocket' the valve head with a small grindstone- and the greatly increased throat diameter (compared to the standard head) copes admirably !
I don't fancy the head gasket modification - there may be trouble ahead..... I hinted earlier that I had only ever used a proper copper gasket -not this 'cardboard' version..... With no flange around these water holes the coolant will have access to the 'cardboard'... Perhaps a trace of silicon sealer around the holes would be a good idea.
Too late for the sealer now, as everything has just been put together.
I will just have to keep my fingers crossed and hope for the best.
I noticed though that the other waterways between the combustion chambers, in line with the offending ones, do not have sealing rings either and they should be OK, I guess.
I also read in another (Mini) forum that people who encountered the same problem as I, blocked off the two waterways close to cylinder no 1 and no 4. What would the effect of this be on the cooling of the head, as effectively you're cutting the flow by 50%.
To avoid fouling the combustion chambers on the exhaust side I had the exhaust valves sunk in the head by 32thou.
I was told that it is an unleaded head from a 1992 Mini (12G940B). However as there were no inserts I was told that Leyland only hardened the surface of the valve seats to make the head unleaded. I should think that while grinding in the exhaust valves, the hardening will have been removed and I will need to use lead-substitute in my petrol as per my old 202 head?
The 998 heads were just 'hardened' (although it's not clear how this was done...) and they certainly used better quality exhaust valves - but the unleaded 940 heads DO have inserts... However - there is NO need to use any additives - just set 15 thou gap on the exhausts - and check/reset them every 3000 miles. If your style of driving does seem to cause the gaps to close up then by all means try an 'additive' - but the only one that actually contains any tetra ethyl lead is 'Tetraboost' - it's the ONLY one that's likely to do any good......
The car has been up and running for quite some time now. Compression is good at 50lbs when hot. The car is a fair bit more sprightly in acceleration than it used to be. I have kept the carb and manifolds original for now but did put on a K&N open air filter. There has been a steady droplet of oil at the front right hand corner where the oilway is though. I have tightened the head just a tiny bit more to see if it stopped but the tiny leak is still there. It is only noticeable after a long hard drive however. Since it is only a few drops of oil, I have decided to leave it as it is. I use Castrol 20/50 classic engine oil and I feel that this is a bit more fluid or thinner (if this is the right word) than other 20/50 brands. Since using this oil has also revealed some sweating on the 1967 Midget I own, I believe using another brand of oil next time could cure the tiny leak. In the old days (20 odd years ago) I used to put Valvoline 20/50 in, but I believe this is not available around here anymore . So for now everything is OK and I plan to put some more miles on the car this year. Next on the list of things to do are Polyflex bushes for the front suspension, but that will have to wait until spring I guess.
Good news - but I'm sure you don't mean '50 lbs' compression ??? You will need a larger carb on a non-heated manifold to get the best from it. Do check/reset the valve gaps - 12 thou inlets and 15 thou exhausts.
no I am sorry, of course oil pressure is 50 when the engine is thoroughly hot after a long run.
I do have a larger carb lying around and I may fit this in spring as well. For now the engine is running sweetly and I want to see how it behaves over the coming months before I start tinkering with different carbs or manifolds, which are still a bit of a mythical science to me. And I haven't read all the chapters in the Vizard bible yet ...
Excellent -as long as it's running well - that's the main thing. If the performance is adequate for you - the economy may well be best with the set-up you have now. Have a look at the plug colours after a hard run and report back. Also worth optimising the ignition timing by advancing it till you get a little bit of pinking - then take it back just slightly.
