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Tuesday, January 31, 2017

Triumph Spitfire Engine Rebuild #10

I've decided to change the titles to "Rebuild" vice "Refresh". I think it tells the story better.

Couple of odds and ends done over the last few visits. I measured the crankcase breather hole quite some time ago and found it to be about 3/4". I went to Napa and sourced a stand-alone 3/4 core plug and put it in. I was hoping to recess it a bit, bit it did fit rather snug. Since I don't expect any real pressure to build behind this plug (unless I screw up the crankcase venting in some way) I'm not concerned for a really good fit. I mainly just want to prevent oil from seeping out. Guess I'll find out eventually!

3/4", though it says .760 in decimal form. Last time I checked, those two were not equivalent!

Plug installed. It is flush with the block.

After that, I removed my old pilot (spigot, as the Brits refer to it) bushing from the rear of the crankshaft and put a new one in. It was in there pretty good so I used a tricked I learned on my favorite forum. The pilot bushing is installed in the rear of the crankshaft and it takes the end of the input shaft of the gearbox. It is not a tight fit, so I think it is for alignment more than anything as you would obviously want the gearbox and motor to be able to spin a different RPMs.

The trick is to pack the blind hole that the pilot bushing is installed in with regular grease. Then, using a rod or something that is just a bit shy of the pilot bush internal diameter, compress the grease. I used a hammer and a 1/2" bolt (the bilot bush is a 1/2" ID) wrapped in electrical tape for a very tight fit. With no where to go, the grease fills in behind the pilot bushing and, as you compress it in there with the bolt and hammer, eventually pushes the pilot bushing out.

Pilot bush just starting to clear the surface of the crankshaft.

Once enough of the pilot bushing was sticking out, I grabbed it with a pair of vice grips and slowly worked it out of there using a rotating motion.

Gripped with the vise grips.

Old pilot bushing out. It was in there pretty good.

Based on how difficult it was for the old pilot bushing to come out, I was concerned with putting the new one in. I cleaned up the hole and the new one slid right in with no problems.

New pilot bushing on its way in.

After that, it was on to cleaning the pistons and measuring the connecting rods. The pistons cleaned up very well and the before and after pics don't quite do it justice.

Before cleaning. The top had looked worse than this originally.

After cleaning. Don't think these things have many miles on them!

Side view. Nice shape.

I was also able to locate the number stamps on the connecting rods. On one side was the number "1", "2", etc while on the other were some random stampings, letters mostly. They did match, however, and it easily kept orientation correct.

This would be number one. The cap and rod match up assembly wise on this end.

Then I needed to measure the small end and big end clearances. Since my bore gauge was not small enough to do this, I used my telescoping gauges. As you may suspect, these were from Harbor Freight, of course. They worked okay, but I did have a specific problem that I'll get to in a second.

The appropriate telescoping gauge is inserted into the diameter to be measured. The gauges come from 5/16" to 6". For the small end, I used the 3/4" to 1 1/4", or there about, gauge. The telescoping gauge is a "T" shape with the "arms" of the "T" spring loaded. There is a knurled knob at the bottom of the "T". You loosen the knob, allowing the spring loaded arms to expand as much as they can. The gauge is inserted into the diameter, compressing the spring arms. I rocked around the gauge a bit to get a good fit, then tightened the knob. This locks the arms in place.

The arms of the "T" installed.

The gauge is removed and measured. In my case, I used both a digital caliper and a micrometer. I got different readings for both, but I assume this to be due to the differences in accuracy and measuring method. The 0.8125 from the caliper was what I was looking for while the micrometer measured a bit smaller. Based on the fact that one measurement was right down the middle and that I could slide the piston side to side on the connecting rod, I called the measurements good.

Telescoping gauge measured in the digital caliper.

And in the outside micrometer.

Since my measurements were good and these bearings don't see the wear that the connecting rod or main bearings do, I decided to leave them in. A visual inspection did not reveal anything abnormal, either.

I did the same thing, using the same methods, for measuring the big end diameter. Like with the main bearings, the bearings were cleaned and installed and the caps torqued to specification. Being an older Mk1 motor, the connecting rod bolts use locktabs. I included, though didn't bend, the locktabs in the bolt up just to make sure that they wouldn't throw my readings off if I didn't include them.

Torqued and ready for measurement.

As with the small ends, the big ends all came in spec. I did have a problem, that I mentioned earlier, however. The telescoping gauge I used for this measurement was faulty. When I tightened the knob to lock it in, it tended to draw in the arms just a bit, making the measurement smaller than it should have been. It took me several times of trial and error to prevent it from doing this. In the end, while I've been happy with every other measuring tool I've been using, I should have spent the extra money on a slightly better set of these. Lesson learned.

Finally, before installing the pistons back on the rods, I weighed the rods. According to the workshop manual, they should all be within 4 drams. That works out, as best I could figure, to about 7 grams. Fortunately, all of my connecting rods were within about 3 grams of each other, so no worries.

My kitchen scale in a foreign land. I didn't tell the wife!

Doesn't seem like much, but there were a lot of cleaning and other iterations going on. I also had done some more stuff that wasn't worth documenting, like measuring the gudgeon pins (they were fine) and other items.

I also make the big decision to get the block bored. Those pits that I mentioned in my brush honing video that I wasn't going to fix just kept gnawing at me. What a waste it would be to do all of this work and the car be fundamentally flawed by an engine that won't hold compression because I did a shoddy job putting it back together. I asked on my favorite forum and it was a unanimous answer.

Outside of the machine work, however, this is going to cost me extra because I'll have to buy oversized pistons. Hopefully the pits aren't too deep (I don't think they are) since I've only got about another 0.020" before I get too nervous about machining out more. I had intended to drop the block at the shop today, but the snow messed that up. I'm hoping for Thursday, now, but we'll see.


  1. You can also remove a pilot bearing with BREAD:


    I wouldn't have believed it if I hadn't seen it.

    1. That's crazy. Grease seems much more appropriate for the job. Of course, the snack after...