Well, we certainly tried to do it "right" but something did not work out.
I broke down and had to get flat-bedded home. When I got the car home I had zero compression in cyl 1 & 2 and only 100psi in 3 & 4. So the bad ones were clearly bad, and the "good" ones were low.
I ordered a boroscope attachment for my phone to look inside before going through the effort to open it up. I could see a ring of metal I initially thought might be a valve seat, but it was the fire ring from the head gasket:
That pointy metal ring was hard to ID; the dark bottom is the top of piston #1.
I pulled the car apart, in a personal best 1:40 and sure enough it was the head gasket. It had shredded in a couple places in Cyl #1, most importantly perhaps between cyl 1 & 2 which is how I got my zero reading. I do the readings with the plugs out, so when piston 1 came up, the pressure it tried to generate leaked into cyl #2 and out the plug hole.
An expert on the Triumph boards asked if the .040 over pistons are too large and perhaps are hitting the fire ring. So I took some measurements. In the race preparation manual they use TR6 pistons - which are .040 over, and then do some other machine work to make it all fit. Here in the Spitfire, the stock head gasket is supposed to be good up to a .040 overbore and up to around 10:1 compression or a bit above. Interestingly, the pistons are beveled on the edge, perhaps to ensure that they don't hit anything:
The piston has some dings in it from the head gasket failure, but nothing terrible. You can see the recess for the fire ring here as well as the bevel on the edge of the piston. This is at TDC for cylinder #1 20139 is the part number for a 9:1 piston (flat top); the overbore is also noted (+040). The arrow is for proper orientation.
The irony is, I suppose, that the recess is there to help with compression and keeping the cylinders from leaking. But it does complicate the head gasket which is really 2 different gaskets. The depth of the recess essentially determines how much pressure goes on to the fire ring and how much goes to the rest of the gasket (coolant and oil). It has to be perfectly cut and clean all the way around. The top of the block is ok, it looks very scratched up but those are old machining marks and aren't big enough to feel with a fingernail. As long as it is flat, the block should be fine. But to ensure the flatness and the correct recess I will probably need to remove the engine and send it out for machining. Still mulling over whether I should put it together one more time first before I tear the car completely apart to remove & rebuild the engine, and there is also who should do that (me, or hire someone)
And there is another detail which could be related. Some installers insist you should have assembly lube on one end of the new studs although ARP does says to lube both ends. ARP also says (as I read it) if you use loctite to hold the studs in place that you should torque the head down before the loctite sets.
It is an interesting problem because blind holes are not precision drilled or threaded so you are not tightening until they hit "bottom" - & they will be too short, well the heights will vary a lot. This was one of my issues - I think. I put them into the block too far and did not leave enough thread above the head for the washer & nut. I also could not use the 12pt nuts that were supplied - I subbed in the old 6-pt nuts from before. 2 of them got a little stuck on the studs and I think that messed up their actual torque spec and may have contributed to my issue. On top of that, you have the studs themselves which seem too free to rotate or vibrate loose. I spoke to a number of folks I know who have built a lot of engines professionally, and the consensus was the make sure the studs were the correct length and would not move around themselves. The torque we apply would all go to the nut pressing down on the washer up top to hold the head on. The washers are very important to have in place. These studs are delivering an incredible amount of pressure.
While the engine is apart I cleaned up the studs, chased the threads with a chaser (not a tap - I have since learned that using a tap is not ideal for this task) and ground down the valves to clean up the seats and help them seal better. I have also pre-measured all of the studs with a nut and washer fitted through the head to mark off the depth the studs should go into the block. This will allow me to make sure that the studs are not screwed too far into the block and will have enough thread in the nuts to hold the full torque.
So the head and block and pistons are cleaned up, the head studs are measured and ready to go in. We'll try this one more time and hopefully we will be a bit more successful.
Here I have the 12pt nut and the proper washer on the head stud at what I'd like to have as a finished height.
I marked off the bottoms with a paint pen, and this told me how far to put the headstuds. I used blue loctite to hold them in place for later assembly. I marked every bolt.
After marking them all, I used Loctite and hand turned them into place at the marked heights by hand. This new gasket is the Lucas brand one; it has a good reputation so we're trying it out.
In general it worked out well. Some nuts don't have 100% coverage (see the one in the rear in pic) Next time I could take actual measurements or have assigned studs in case various spots were different thicknesses. But I think this will be fine. We'll see. I followed the ARP procedure again - using the stock head-stud pattern and tightening to 1/3 of the final value through 3 rounds, so 15 all around, then 30 and finally 45ft/lbs.
Head is on, rockers are in place and I have marked off the fasteners that have been torqued to spec with a yellow paint pen so I know where I've been, and if anything is moving around. A good tip I got from the good folks at Butzigear.
The rest of the engine assembly is pretty standard (and covered in the prior article although I may smoosh these both together and shorten it a lot)
The engine started up, had a few water leaks and a small exhaust leak. Otherwise it sounds good so far.
The key thing (hidden down here ath the end of part II? Really?) is that when you go to start it up again, disconnect the coil. This lets you turn it over for a while (I do 30-45 seconds) to pump oil around the engine. Then you can connect the coil again and try to get it started. But make sure you have nice new clean oil on everything you possibly can first.
Nothing complicated or dangerous. Just pull out the big wire to the distributor.
May 30 Update
After fixing the leaks, I got her started up, checked the ignition timing (set to 10 deg advanced) filled it up with super (91 octane) and have been taking progressively longer and longer drives. I'm at around 50 miles so far in total, already farther than the previous attempt. I am keeping the RPMs under 3,000 for now and taking it easy on the throttle.
This weekend I'll change the oil, put in real coolant (it still has the plain water from the re-assembly and testing) and check the torque on the head studs.
Engine heat is stable and pretty low. I won't need the electric fan by the look of it. Its starting well and running very smoothly. So far so good; hopefully this one is going to take.
June 1 Update
I ran the car up to temp and then shut it down to take a compression reading. All cylinders read about 135-145psi except for cyl #1 which read a bit low at 120 psi. I drained the oil once that reading was complete.
Once the engine had cooled, I checked the torque on an exposed head-bolt and got about 20 degrees of rotation out of it. So I removed the rocker shaft and went over all of them in the standard order shown in the manual. I did not back them off one at a time, I just turned them from where they were. Then I re-installed the rocker shaft, set the valve clearances, and set the timing to between 8-10 deg BTDC with a timing light and idle at 900RPM.
I re-checked the Cyl #1 compression once the engine was hot again, and now it read 135psi. I was surprised it had moved so much, especially since the car has not gone that many miles since the head work. (under 100 miles) but there we are. Compression testers are not very accurate and old timers will generally tell you to focus on all 4 cylinders being within 10% more than the actual reading, and also not to try to infer your CR from the reading either. "In theory" if both valves are closed during the compression cycle you should get a reasonable relationship of CR to pressure. 14.7psi is sea level and 8 times that would give you 117.6psi for a CR of 8:1 in theory. 140psi would equate to 9.52:1 But this isn't a good measurement to do this way due to how your camshaft is timed. There is overlap, and they have to start opening early (in order to open fully in time) and things like that. "Its complicated" So I am just happy that all 4 cylinders are in a good range now and the car is running smooth and strong. (so far, so good!)
Comments