My buddy purchased a soda blaster for his business, which came very handy for cleaning the engine. Definetely not a fun process, but it’s worth it.

Heads before soda blasting

Heads after soda blasting

Soda blasted engine block. Looks like it just came from the factory.

Quick clean up of the valve faces

The valves looking pretty good after a quick lapping job.

Checking the valve seal using compressed air. No bubbles!

A little scotch brite to clean the pistons. Make sure to seal all the holes in the block first.

After lapping the valves, I did another leak-down test. The results were much better this time, but still pretty inconsistent. The worst cylinder had 25% leakage and the best 7%. I put a little engine oil in the cylinders to see if it would seal a little better, but I noticed no improvement. You could clearly hear the air passing through the piston rings. Since my build is on the budget, I decided not to continue with the cylinder job. The scrap yard was nice enough to take the engine back and give me a full refund. It was a little disappointing as I spent quite a bit of time on it.

LM4 after I was done cleaning it. Too bad it had to go back.

For the next engine I decided to spend a little more and get an L33 aluminum block. These came with 799 heads, which are pretty much the same as the ones that came on LS6 Corvette engine, minus the sodium filled valves. It was a little overpriced at $1200 CAD, but I couldnt afford to sit around waiting for a good deal. The engine looked pretty clean, and only had 80,000 miles.

L33 Aluminum Block from 2005 GMC Sierra 1500

Got straight to work

799 Heads

I took the heads apart and as expected the valve faces and seats were pretty gunked up and pitted, not to mention all the crap and leaves that were in the cylinders. Since I didn’t have money to get the valves recut, I decided to lap them. Most people are against this, but this is a budget build, so screw it. I used a hand drill and a little piece of air hose to do the job. Again, most people advise against this, but there was way too much pitting to do it by hand.

There was a fair amount of buildup and pitting on the valve faces

The seats weren’t as bad, but they definitely needed some lapping

Lazy way of lapping the valves using a hand drill and a piece of air line. You have to be really careful when using the drill, its pretty easy to screw up. Make sure to lift off pretty often and switch rotation. Also keep checking the seat width to ensure you stay within the spec. Of course the best way is to get them cut at the shop, but if you must, a hand lapper is the next best thing.

You can see that the valves still have some pitting, but I wanted to stay within the seat width spec.  Lapping the valve more would look nice, but it would cause all kinds of problems in the long run. From what I read, a wide seat allows for too much heat transfer from the valve, which can cause some serious carbon buildup.

I decided to check the engine to see what kind of condition its in and if it would need a tear down. We built a leak down tester from some parts my dad had laying around and hollowed out a spark plug to make a fitting (I will do a full write-up on how to build one). Long story short, all the cylinders but one had zero compression. You could pretty much hear the air coming from all the valves, so I decided to take the heads off for a some cleaning.

Home built leak-down tester. Just some simple NPT fitting and gauges. Pretty easy to make, except for hollowing out a spark plug. I will do a writeup on how to put one together in the near future.