Illustrated rebuilding of a L36 into a supercharged 3800... - Page 7 - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


Performance, Brainstorming & Tuning Talk about modifications, or anything else associated with performance enhancements. Have a new idea for performance/reliability? Post it here. No idea is stupid! (please use Detailing and Appearance for cosmetic ideas)

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Old 01-13-2007, 01:25 PM   #61
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No pics....
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Old 01-14-2007, 12:05 PM   #62
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Ok, with the heads taken down and cleaned of carbon (or at least as much as I could scrape and wash out) time to start the inspection process.

First, the head needs to be checked for warpage. You need a good machinists ruler/straight tedge to do this (one of the I-beam types) Lay it across the machined surfaces and use feeler gauges to measure any gaps. The critical one is the head-to-block deck surface, since this will provide the clamping force on the head gasket to seal it up. These check out pretty well, so we'll keep on trucking on the rebuild.

If the head is warped, you have two choices:

1.) Rebuilt or New replacement heads. Considering the price of the heads, this is a viable option. Same will hold true if any of the valves or guides are screwed up...it'* the law of diminishing returns in action. The cost to fix the head can soon exceed the cost to replace them. (There are a few motors in the world that are so rare as to warrant doing a lot of work to refurbish the original parts, since the replacements are made of pure "Unobtainium"...the Series II 3800 is not one of them.)

2.) Resurface the existing heads to square them back up. Note: This has some negative effects as well. Removal of material from the head means the chamber volume of the heads is reduced, also, the intake manifold may also need surfaced too..since the heads will sit a little lower and move the intake manifold flanges down closer to the block deck.

Another important little tidbit involves the block deck surface. The machine shop checked that for me and did not have to resurface the deck. That'* good news to me, the 3800 is NOT a "zero-deck" motor (as we'll see when we reassemble the block) The pistons extend beyond the block deck into the head gasket area. Any change to the block'* deck would mean either shim head gaskets or machining the pistons down so they don't hit the head.

But we were talking about cylinder heads, so here are a pair of cleaned up valves:



The top valve is the #1 exhaust valve, the bottom one is #1 intake. Note the long silver "scratches" down the stems...they aren't scratches at all, just the reflection of the camera flash on the hard-chrome finish of the valve stem. Each valve is made of two parts. The stem is hard-chromed steel to give it long wear in the guides. The "Valve" is a milder cast steel that has been brazed to the end of the stem. It'* done this way so the mating surface of the valve to the seat can be ground to a good seal.

Cleaning the valves is pretty simple. Soak them in solvent, then scrub the carbon off. When they are clean, check the diameter of the valve stem with a micrometer. You are looking for any taper in the stem that would be an indication of wear and allow the valve to rattle against the valve seat. Also, if the motor was starved of oil, you would see a lot of wear down here.

Last, check the width of the seat area on the valve. If it gets too wide, then the valve needs to be replaced, also if any ridged have formed on either the lip of the valve or it'* seat in the head, both will need to be remachined or replaced.

With the valves cleaned up, the valve guides in the cylinder head need to be cleaned out. A 30caliber rifle bore brush (phospour bronze, not steel) is the perfect fit to scrub out the guides. You can check the diameter of the guides with a set of pin gauges, however I found this to usually be a waste of time. If you didn't find any damage on the valve stems, then it'* highly unlikely there is any problem with the guides. If you do have a problem with a valve stem, then the only solutions are to ream the guide larger and use an oversize valve..or ream the guide WAY oversize and install a sleeve to restore the original bore diameter to the guide.

Lapping valves....

With the valves ready for reassembly, the seats need to be lapped using the actual valve that will ride on it. Lapping compund is like liquid sandpaper. It has a fine grit (around 600) and a little smear of it around the lip of the valve is all it takes. Apply a little pressure to the valve to force it against the seat and spin it in the bore. That will polish both the valve and seat together, giving you a nice tight seal when the valve is closed. Clean it off with solvent when you are done.

Here'* #1 cylinder valves ready to be lapped into the seats:

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Old 01-14-2007, 12:40 PM   #63
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Here'* a better view of lapping in action:



See the dull grey ring on the exhaust valve, that'* the surface created by the lapping compound. It should be uniform in width, and not missing any spots. This is a visual sign of where the valve surface is in contact with the valve seat. For the factory 3-angle valve job, that'* about the right width. For a competition 5-Angle or 7-Angle valve job, the contact area is much thinner. The radius of the both the valve and seat is smoother, so they get a little better airflow.

Down side to a multi-angle valve job is that they don't last as long as the 3-angle factory valve job. Yes, they flow better, but the seat surface is thinner. Since many racers run heavier than stock valvesprings, the force applied to the smaller valve seat surface is higher. You'll see "peening" or dents in the valve seat surface forming sooner.

High-end valve tricks like "Swirl Polishing", more angles, etc. do work, for a while, on race motors. If you are looking for max performance, I recommend doing it and living with the higher cost over the life of the motor. But on a street motor, carbon build-up on the valves and seats will render these tricks useless in a few hundred to a thousand miles. I guarantee that is you pull the heads of a street motor after a few thousand miles of use, they will look just as nasty as these did when I started cleaning them. Running without EGR, and a good fuel-air mixture will keep them cleaner and make the tricks work longer, but in the end, the valve job will wear out and have to be redone.

Hence, I'm going to stick with the factory valve job. It'* not as efficient, but will last longer in the application this motor is going to be used in.

When each valve is done, a little wrap of masking tape on the valve stem on top will keep the valves in place and protect the seats until we're ready to finish assembling the heads.
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Old 01-14-2007, 04:32 PM   #64
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With the valves lapped back in, we still have some more finishing work to do on the cylinder head.

All of the threaded holes need to have the threads chased with taps. And there are a lot of holes to be done, so get comfortable. You will need the following bottoming taps:

1/4"-20 is used on the valve cover bolt holes.
5/16ths-18 is used on the intake and exhaust flange bolts as well as the rocker arm bolts.
M10-1.50 is used on the exterior bolts
M14-1.25 is used on the spark plug holes



After a loooong coffee break from threading holes, the next operation is to gasket match the cylinder head intake ports to the intake manifold gasket (On this one, I'm using FelPro MS95977 gaskets)

The process is pretty easy, tape the gasket to the head and scribe the outline of the intake port in the gasket to the cylinder head. It may not seem like a lot of metal hanging out into the airflow, but every little bits helps, and this stuff is free.



I'm not going to go very deep into the intake ports. The goal is to break the sharp edge of the intake port casting that sticks out beyond the gasket. The same operation is going to be done on the intake manifold.
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Old 01-15-2007, 02:36 AM   #65
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Aren't you swapping on L67 heads? Or are you putting your injector bosses into an L67 LIM?
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Old 01-15-2007, 02:39 AM   #66
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There is a L67 head in the pic above. You can see the injector boss is in the head.
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Old 01-15-2007, 08:21 AM   #67
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Quote:
Originally Posted by willwren
Aren't you swapping on L67 heads? Or are you putting your injector bosses into an L67 LIM?
Yes, I'm swapping on L67 heads, but the pair I got from Ed Morad were still used ones and need a good "going-over" to get them ready for use.

The original L36 heads are going to get cleaned up as well. Haven't decided what to do with them yet. I offered them to Ben before Christmas, but never heard back from him. They will either hang around here, get sold on eBay, or..if the mood strikes me..get injector bosses milled into them and be converted to L67 heads.
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Old 01-16-2007, 05:15 AM   #68
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Quote:
Originally Posted by clm2112
I offered them to Ben before Christmas, but never heard back from him.
Dude, I totally forgot about that! Gosh, I feel like a jerk....
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Old 01-16-2007, 08:07 AM   #69
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Quote:
Originally Posted by big_news_1
Dude, I totally forgot about that! Gosh, I feel like a jerk....
No sweat, I get all screwed up over the holidays. Yeah, our conversation about the heads is what started this thread. I went to pull them and get them ready to ship when I found the mess inside the cylinders and started the whole rebuild thread.
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Old 01-16-2007, 10:16 AM   #70
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Oh, before I forget, there'* another step in cleaning out the cylinder head. The head bolt holes and injector bosses need scrubbed out too.

To do this, I chuck a 20ga shotgun bore brush into an electric drill and pass it through all the head bolt holes and into the injector bosses. The injector bosses need a smear of grease on them when done, just to keep the O-Ring surface clear and ready for the injectors during assembly.

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