01-10-2017, 01:28 PM
Oh dear! Whilie running the engine on my Nippy I recently noticed traces of black oil coming up past the centre cylinder head stud accompanied by occasional bubbles. So "off with its head" and go for a decoke, the first for 10 years and 3000 miles most of which were to Beaulieu and back in 2012. It certainly needed that; I've never seen such a roasted gasket before! All was cleaned up nicely with my grandson's enthusiastic help and the valves reground and fitted. Then when it came to re-fitting the head, an original 9E Nippy head, I noticed it was cracked! All the way across the top of the casting from the sparking pliug hole, round the edge and partially along the flat surface over cylinder No. 2. Ripe expletives!
So, while sorting out what to do about this - repair with metal stiching? new head? - I decided to fit the Supalloy head that the Nippy originally had when I obtained it in 1968. This went without a hitch - nice layer of grease on the HC gasket, cool the head in the freezer and fit it while cold, run the engine. Perfect! Then fill with cooling water and run engine again. Perfect again! Lovely smell as the excess gasket grease that had squeezed into the cylinders burned off!
A couple of days later the car would not start, it seemed almost like a kick-back as if the ignition were far too far advanced. A bit of investigation showed that water was leaking into the cylinders, particularly 1,2 and 3 and to a lesser degree No. 4 as well. Of course some water also got into the sump! What mystifies me is that the gasket should have been so very leaky. From "reading" the gasket it appears that the water may have been emerging from the central water passage, next to the central head stud since this passage in the Supalloy head is not concentric with the passage in the gasket and, in addition, is slightly corroded on one side. The surface area of the gasket that should seal this area is very small. I am also wondering whether I applied too much grease to the gasket and that the thick grease layer could be burned away from the cylinder(s) to the water passage(es) thus forming an escape for the water. Does anyone have any thoughts on this?
What I also noticed while examining all this is that neither a low compression nor a high compression gasket really fits either cylinder head properly. The LC gasket has more "meat", covers the sealing head surfaces better but also overlaps the edges and the head side of the gasket is exposed to the gases in the cylinders. I think I may have originally used LC gaskets with the supalloy head when I first had the car since I still have one of those non-copper (fibre?) LC gaskets and I do recall that this type of gasket was the only one that ever "blew" back in the 70s. All things considered it seems to me that the HC gasket is the most appropriate though two sources have advised me to fit an LC-shaped gasket.
In all this I should mention that I have not checked how flat the heads are - that would now be only relevant for the Supalloy head.
In the meanwhile I see that new 9E heads are available from Seven County Austins - maybe that's the way to go!
I'd really appreciate any remarks and ideas about this business. Thank you everyone for your help!
Best wishes
Steve
So, while sorting out what to do about this - repair with metal stiching? new head? - I decided to fit the Supalloy head that the Nippy originally had when I obtained it in 1968. This went without a hitch - nice layer of grease on the HC gasket, cool the head in the freezer and fit it while cold, run the engine. Perfect! Then fill with cooling water and run engine again. Perfect again! Lovely smell as the excess gasket grease that had squeezed into the cylinders burned off!
A couple of days later the car would not start, it seemed almost like a kick-back as if the ignition were far too far advanced. A bit of investigation showed that water was leaking into the cylinders, particularly 1,2 and 3 and to a lesser degree No. 4 as well. Of course some water also got into the sump! What mystifies me is that the gasket should have been so very leaky. From "reading" the gasket it appears that the water may have been emerging from the central water passage, next to the central head stud since this passage in the Supalloy head is not concentric with the passage in the gasket and, in addition, is slightly corroded on one side. The surface area of the gasket that should seal this area is very small. I am also wondering whether I applied too much grease to the gasket and that the thick grease layer could be burned away from the cylinder(s) to the water passage(es) thus forming an escape for the water. Does anyone have any thoughts on this?
What I also noticed while examining all this is that neither a low compression nor a high compression gasket really fits either cylinder head properly. The LC gasket has more "meat", covers the sealing head surfaces better but also overlaps the edges and the head side of the gasket is exposed to the gases in the cylinders. I think I may have originally used LC gaskets with the supalloy head when I first had the car since I still have one of those non-copper (fibre?) LC gaskets and I do recall that this type of gasket was the only one that ever "blew" back in the 70s. All things considered it seems to me that the HC gasket is the most appropriate though two sources have advised me to fit an LC-shaped gasket.
In all this I should mention that I have not checked how flat the heads are - that would now be only relevant for the Supalloy head.
In the meanwhile I see that new 9E heads are available from Seven County Austins - maybe that's the way to go!
I'd really appreciate any remarks and ideas about this business. Thank you everyone for your help!
Best wishes
Steve