Back on the Road but still not quite right

Got the GT6 back together this afternoon after replacing the manifold gaskets. However it's still pinking and making a noise under load. I'm pretty sure the noise is coming from under the bonnet rather than the exhaust system and it seems to be associated with the pinking,.

I did do a compression test while I had the manifolds off as I was a bit concerned that the noise could have been a blowing head gasket and I didn't want to have to take the manifolds off again if it turned out top be the head. Obviously as the car was apart the engine was stone cold when I did this so there was quite a lot of variation in readings, however none were really low so I carried on and put the manifolds back on. Anyway now the car is together I've done a hot compression test and it looks ago to me, readings are:-
Cylinder                                          PSI
1                                                      220
2                                                      240
3                                                      240
4                                                      230
5                                                      240
6                                                      220

There is less than 10% difference between highest and lowest which is within tolerance. Readings look pretty high but that could just be the gauge, the cheaper gauges don't tend to be calibrated and accuracy in terms of actual pressure is debateable, but the important thing is there are no cylinders with considerably lower pressure or any big variation. For the hell of it I did squirt some oil down the plug holes of the cylinders with the lowest readings and they did improve (up to c270 psi so there may be a little wear in the rings/bores but nothing too serious.

The ignition timing is around 10 deg BTDC at idle tested with a strobe, this is about right but I will try retarding it slightly to see if that sorts the pinking. The rasping noise is a bit of a pain though as I can't find where it's coming from...
 I thought the Engine had about 85,000 miles on it but checking the MOTs it looks like I've only done about 55,000 miles since I fitted it the Engine in 1993 so it's not a particularly high mileage unit so I'm hoping it doesn't have too much of a carbon build up as I know that can be a cause of pinking.

All my recent fill ups of fuel have been Shell V-Power so I don't think is a crap fuel issue.

I'll also give the carbs a tune.

Manifolds back on

I started putting the manifolds back on having got hold of the gaskets. Seems that the manifold gaskets are not as good as they used to be, the one fitted before had metal reinforced rings around the inlet and exhaust ports. I have a couple of new ones from 2 different suppliers and both are just plain gasket material so not as good and I bet they won’t last as long as the one I took off, this was fitted way back in 1992 when I replaced the Engine!


Anyway made up a couple of replacement studs where the nuts had seized on to old studs and they had come out of the head but couldn’t remove the nuts. I cleaned the threads on the head with a tap where studs need re-fitting with a tap and cleaned the studs that remained in the head with a die nut.

Cleaning the Threads on the studs with a Die Nut.

Cleaning the threads out in the head with a Tap.

I then fitted two replacement core plugs using blue hylomar to aid the seal and drifting the plugs into place carefully using a suitable sized socket.

Plenty of blue hylomar in the core plug hole.

Plenty of blue hylomar around the new core plug

Using a suitable sized socket as a core plug drift, tap into place carefully with a hammer.

A replacement Exhaust Downpipe manifold gasket was then fitted with a ring of fire gum to aid the seal. The New Manifold gasket was then fitted, I always grease my gaskets lightly before fitting, helps them, to seal and also helps next time they need to be removed. A little trick my Dad taught me years ago when teaching me how to fix motorbikes.
I then fitted the manifolds. As I said in my last post the lower ones are really awkward to get at, however Marcus advised that a 3/8 drive universal joint, extension bar and 3/8 drive socket would doe the trick. Thanks Marcus this did work a treat.

Using a 3/8 drive socket, universal joint and long extension to do up the hard to get at lower central manifold nuts

That’s it for the evening, I don’t think I’ll get a chance to finish off before the weekend now, as it’s my son’s birthday at a theme park tomorrow I’m out for lots of beers at a work re-union do in London on Thursday, a dirty job but it’s got to be done!