Took the head off. Thanks 1018cc for your help, knowledge, garage.
Why'd we take the head off? Driving home from dropping the boy at school yesterday, I revved it hard in first, it went bang, and started sounding like a mower.
So the immediate thought was head gasket. Got it home (very, very slowly), Nick suggested using DrMini's individually calibrated compression tester (i.e. a thumb, this time with a wet rag over it), and there was very little compression in cylinder 2. Removing the plug from cylinder 2 also showed no difference in sound (i.e. it didn't suddenly drop a cylinder).
So, we pulled the head today. This was informative. The gasket was intact.
The metal between cylinders 2 and 3 was blackened, though. And Nick's since discovered that the head's 0.006" (roughly) out of straight...
0.006" high in the middle.
Other things that we found? Well, I now know that my engine is a 1303 (0.030" overbore). There's still honing marks on the bores.
I've got 1.401" inlets, 1.151" exhaust (maybe it's 1.156", we were using a plastic vernier and it was by the light of the flouro!), with hardened inserts. The head is massively ported, the chambers significantly shaped.
All very good news.
And the biggest discovery? The quantity of coke in the engine.
I have photos that are scary! Layers and layers and layers of coke, on the pistons, throughout the chambers, all up the exhaust port... Even caked on the back of the inlet valves!
Caked rather thick - there were sections on the pistons that I would've put at 1mm or more thick!
When this thing goes back together, it should run much, much better. It might well not run on anymore, given the engine will be quite a bit cooler internally...
And maybe one day I'll get around to finding a pair of twin HS4's... The HS2's are
definitely the limiting factor on this engine. Ported head, decent valves, reshaped combustion chambers, big extractors... Intake breathing's the weakest link.
) after his car had a BHG. I think I've worked out the problem, head is bent 0.006". So it has to go to the machine shop before we can put it back on.
