Friday, April 14, 2017

Triumph Spitfire Engine Rebuild #17 - Piston Installation

Continuing with the rebuild, the pistons were up next. The machine shop had called to inform me that they only needed to take another 0.010" off the bores to get rid of the pitting from the rust. Armed with that information, I gave a call to Moss Motors and ordered a set of 0.030"-over pistons (part number 814-543). Like most piston sets, they came with the pistons, manufactured by County in Taiwan), full set of rings (manufactured by Grant), wrist pins and the circlips.

All told, with shipping, it was about $245. Their prices were comparable to everyone else and, being in VA, they were relatively close. Unfortunately, they didn't have any in stock in VA, so they had to come from their CA warehouse. All told, it took a week and I had them sent directly to the machine shop to save an extra day.

First item was to install the rings, which are installed from bottom to top. This is done because they do not fit tightly in the grooves and it would be relatively easy to break a ring trying to get it over another one if you started from the top. The package that the rings came in was kind enough to indicate this.

The plastic bag the rings came in, denoting ring numbers and a note​ to install in reverse order.

Before installing them, however, I checked the ring gaps inside the cylinder. The two compression rings, one at a time, are put inside the cylinder. The an inverted piston is used to push the ring several inches down the cylinder. Using a piston ensures that the ring is level inside the cylinder. Then a feeler gauge is used to measure the resulting ring gap. Thankfully, all of the rings were of the right gap and I didn't need to file any down.

Forgot to take a picture of this, but here's one out of the manual.

With that done, it was time to install the rings on the piston, the oil ring first. This is a three-piece set up for the Spitfire (and most other pistons in my experience). There is a corrugated expander ring and two thin rings that go on the top and bottom of the expander. The expander ring is corrugated to rapidly collect the oil and return in to the sump through the groves in the side of the piston wall.

Expander ring. The full red and green portions, not being overlapped, denote proper installation. Nice touch.

The two thin seal rings go on next. They work independently to provide the maximum oil removal. I offset the ring gaps by a few inches just to be sure. Probably not as important here as with the compression rings, but there you go.

The two seal rings installed, the gap on the lower one being evident just off to the right a bit.

The compression rings were next. They were each of a slightly different design, one ring having a step in it while the other was fully square. There was also a marking on each for "TOP" so it was obvious which way they went in. Some rings use a dimple or some other way to mark the top, so it's important to know which method the rings that you have use. The top ring provides most of the seal against the cylinder wall while the lower ring provides the rest. For this reason, it is important to offset the ring gaps by a few inches so that you don't provide a straight shot for blow-by.

Top. Got it.

Unless you want to break a ring, I highly recommend using piston ring pliers. For the $8 from Amazon, they are cheap insurance against breaking a ring.

I repeated the ring installation process for all of the pistons and installed them onto the connecting rods, attaching the circlips. Like with the main bearings, I cleaned the heck out of the bearing surfaces with Brakleen and got the crank pin bearings installed as well.

Rings all installed. Tags designate the piston number.

To get the pistons in requires a ring compressor. I picked one up at Harbor Freight. Based on the size of these pistons, however, I would recommend a different set as this one had problems staying circular when it got to the small size of the piston. With some work, though, I was able to get the rings compressed enough to clear the cylinder walls.

Just before installing the pistons I cleaned the cylinder wall with Brakleen and wiped it down with a lint-free cloth. Then I liberally applied 10w-30 (cheap-o oil that I used when I was trying to do the cylinder honing) to provide lubrication.

Oiled up. I used a clean, latex-gloved hand to spread the oil evenly around the cylinder all, changing the glove for each cylinder.

I rotated the crankshaft around so that wouldn't contact the connecting rod when installing it. Then I set the piston, with the ring compressor, in the cylinder with the "FRONT" marking on the piston top point towards the front of the motor. Then, using the wooden handle of my hammer, I knocked the piston down into the cylinder. You don't need to knock the heck out of it. If you do, something is wrong.

Ready to start tapping in the cylinder.

I repeated this process for each piston. I did not bolt the connecting rods up to the crankshaft yet, however.

She's in! I put them all in to this depth before bolting them up.

Once all the pistons were in, I rotated the crankshaft as necessary to bolt up the connecting rods. Again, I cleaned the heck out of the bearing surfaces, applied the assembly lube, and bolted them up, but not torqued.

Bolt installed. The older motors used lock tabs, which is the bright metal you see under the bolt head.

Once all the bolts were in and snug, I went back to start torquing them down to the required 42-46 ft-lbs. As I started to torque one of the bolts, however, it just wouldn't tighten up. I gave it a few more turns and decided to stop as something was obviously wrong.

I pulled the bolt back out and looked for stripped or damaged threads. Not finding any, I decided to try a different bolt and got the same result. This was pretty frustrating as I now thought I had a connecting rod problem. I pulled that bolt out and inspected in a bit more closely. I put it against the other one that wouldn't tighten and another that I hadn't installed yet and it became obvious that the bolts were stretching, done playing bolt for the rest of their lives.

L to R: "Good" bolt, the second bolt and then the first bolt.



Closeup with obvious stretching and elongation on the right-most bolt.

I queried the gang on my favorite forum, concerned that I had other problems and not just bad (old) bolts. Based on the symptoms, the consensus was that the bolts had just had it and new ones were in order. Thankfully, I was able to source original bolts from a forum member. These were still in the original box (love that old stuff) with 50 year-old masking tape protecting the threads.

Three of the bolts that were still solidly in the masking tape.

The original British Leyland box.

At some point, the bolt design was improved to no longer require the use of locking tabs. So, with these bolts, the locking tabs were not installed but I did put some Loctite Blue on them just to be safe. All went in smoothly and all torqued down with no issues.

All pistons installed, though no bolted up in this picture (reason they're all at same height in cylinder).


Up next is head and camshaft installation.

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