L20B Rebuild

[IvyCap]

This is my first time rebuilding an engine and have been using guidance from a combination of the service manual, forums, the "How to Rebuild Your Nissan/Datsun OHC Engine" book by Tom Monroe, and YouTube for the teardown.

 

Starting a rebuild on an L20B w/ U67 head that came with a 510 wagon that I purchased a couple years ago. Some things I've noticed upon inspection during the teardown include a corroded section on the timing cover where the water pump is as well as some witness marks of the valves touching the pistons.

It looks like the engine has been rebuilt in the past judging by the flat top pistons (from a 280zx? correct me if I'm wrong), aftermarket gaskets, and RTV. 

 

I plan on getting new valves, but is there anything I can do to salvage the pistons? Or should I just move on and get new pistons?

 

My goal is not to make power but to make the rebuild simple and reliable. As close to stock as possible would be ideal.

 

[datzenmike]

Measure the bore on another cylinder. If 86mm then from a '81-'83 280zx.

 

Then measure the bore much more accurately about 1/2" down in the front and back direction, then at 90⁰ to that, then at 2" down and at right angles, and last at 3" down and at right angles. Record these measurements. From this you can determine if the cylinder wear is tapered or oval. If within specs pull the pistons hone the walls and put new rings on.

 

Do all the pistons have the valve marks???

 

As long as the valves can be re-faced and I assume new valve seats put in, they don't need replacing. 

 

Picture of the water pump area on the timing cover. Mine had some erosion on the case near the impellers. I use JB weld

 

 

 

[IvyCap]

My timing cover is far more corroded than what you have shown. Verdict?

 

Also yes, all the pistons show the same valve marks on them. See below for a side view.

 

I ran into another potential issue which is the clogged coolant jacket ports. I picked out the gunk and it looks like a decent amount of the surrounding material has corroded as well. How bad does this look?

 

And cylinder 3 and 4 intakes look wet with oil at the base of the valve guide so those likely need to be replaced

 

Lastly, cylinder 4 exhaust valve guide is definitely going to need to be replaced

 

The real questions is, at this point does it seems worth it to rebuild given the work the head needs? And is the corrosion bad enough to just look for a new head?

[Stoffregen Motorsports]

That's a good head. Though low compression, it's got big valves and is a great head for a big bore 2200 or 2300.  I'd see about having someone weld the head to be able to use it.

 

Whatever you do, do not throw any of those parts away. Even if you;re not up to the task, someone can weld up the head and machine it to be usable again.

 

Also, never remove the cam towers from the head if you can help it. Yes, they have alingment dowels, but sometimes replacing them can take time to get them lined up well enough for the cam to spin freely.

[IvyCap]

I guess too late on the cam towers as I already removed them as a unit with the cam still in place. 4 of the 8 bolts were loosened just by finger so I don't think they were doing much if that helps.

 

I definitely won't be tossing anything and I'm bagging and tagging everything as best as possible.

 

I'll ask around and get quotes for welding and machining the head to start.

[Stoffregen Motorsports]

Where are you? I know guys who can weld that head up.

[Stoffregen Motorsports]

Oh, and welcome to Ratsun...

 

And all that bullshit.

[IvyCap]

59 minutes ago, Stoffregen Motorsports said:

Where are you? I know guys who can weld that head up.

Los Angeles. Any recommendation in my area? I see that you are up north.

58 minutes ago, Stoffregen Motorsports said:

Oh, and welcome to Ratsun...

 

And all that bullshit.

Thanks. Long time lurker but never made an account. 

 

 

I might even try and source another head if possible and just cut some losses.

[datzenmike]

 Hard to imagine revving an L20B so high the valves float above the seats that the piston hits them closing. As soon and the valve starts to float the engine looses power and should struggle to rev higher. With all four it would act like a rev limiter. I can see putting the head on without setting the cam timing to match the TDC on the crankshaft. Then spinning the engine around could hit something in all cylinders. Spinning the cam would only affect two pistons at most. It's just weird.

 

Timing cover has got to go. That rusty crap and the erosion of the head passages is from running water and not a water/anti-freeze coolant mix like the old owner should have.

 

Below...

The guides have been knurled before. A machining process that displaces metal making a worn hole narrower. Then it is reamed to the correct clearance. It avoids knocking the old guides out and pressing in new ones and reaming them to size. I have a 340 head done in the '70s.  This is much cheaper than replacing them the only down side is if you ream a guide that is worn out and really needs replacing. 

 

 

ABOVE. It appears that larger valves may have been put in, so wider valve seats. To me it looks like a step below the valve seat was not machined away. You could do it with a dremel. That 'step' will impair smooth air flow in or out.

 

 

 

 

Keep in mind that this much erosion is also in the coolant passages inside where you can't see the damage.

 

It's all fixable.

 

[banzai510(hainz)]

get this Japan made pump if using the stock type 510 4 blade fan.  cast impeller

 

front cover looks good enough.

the head with the water passage erosion. I had this on my L16 with L20 head.Not running good antifreeze,change out every 3 years or so).  I had to put a new head gasket and it stopped leaking out by the fuel pump area for my head

 

https://www.ebay.com/itm/295894480263?fits=Model%3A510|Make%3ADatsun&epid=74483302&itmmeta=01HQB3YWTMNWK65WP9ZQT8BD5R&hash=item44e4af7587:g:HTYAAOSwhXRlv8fo&itmprp=enc%3AAQAIAAAA0HZkvOnIz5Sejztg%2Bzq%2FBUXtlsBRw1MRU%2Fe6eI3hfeiXL80iRm4cCBktx1JBzgX46Ym%2B8%2FFhvKauv6FkgI5fU7F7kQeAwhnx6L5mvYOxrdSB%2FdGCt%2FMdii5x1tezlvhPswTzGvDODMP0ClTSSsqVB7q0ZpnJbhc2Btd6DRTHh6OGH%2Bp9aHA2doPXKEuMwLz2F3PGXj%2BfSKwQRUUfLe7uz8xAlwBjl135DNjzzyJ0acDISfGIqVglj8PMYH%2FWXLAylSsyVn5%2Ftc39GOskT4RCLsM%3D|tkp%3ABk9SR7bN--O6Yw

Edited February 23 by banzai510(hainz)

[Stoffregen Motorsports]

@IvyCap no, I don't know of any shops in LA, but with all the hotrod and racing shops around there, shouldn't be hard to find someone. I'd start with a local engine machine shop and see who they would recommend. Heck, they may even be able to cut the head enough to get a clean area around that water passage.

 

Mike, flat tops and big cams - it's easy enough to make piston to valve contact with that combo. And it's easy enough to cut the pistons for clearance. You can even do it with the bottom end assembled. Take a couple old valves and weld three spots on them, then grind those welds to form a cutting edge. Stick the valve in the head and put the head on. Attach a drill to the new cutting valve and go to town! Done it. It works in a pinch.

[docbainey]

Slover's Porting Services

Address: 709 Arroyo St, San Fernando, CA 91340

Hours: 

Open ⋅ Closes 6 PM

Phone: (818) 768-0155

 

This place, I believe, used to do the Datsun Comp stuff in the day.

 

[Stoffregen Motorsports]

Good call.

[iceman510]

Cam towers are not that big a deal.  The process is to install them on the head with the camshaft with the bolts snug.  Then you can hit them with a rubber mallet to settle them until the cam turns freely.  Fully tighten them, then check again.  I have had to do this a few times and it works.

 

Typical cylinder head stuff like replacing seats, guides, etc., and doing a valve job should be considered even if you buy a different used head.  Unless you get something already done, no guarantee it might not need the same work.

[datzenmike]

 

DO NOT OVER TIGHTEN!!!!!! THEY WILL STRIP!!!  Someone will say but 5 pounds seems right. One side has headbolts clamping them so no need to tighten them too much.

 

 

[IvyCap]

I ended up finding another L20B but with a W58 head and smog equipped. I removed the valve cover and water pump to get some basic visuals on the condition.

Crusty but the condition looks much more promising than the initial engine. Also looks like it hasn't been rebuilt which hopefully means less detective work.

 

I'll save the L20B/U67 for future build someday.

[Stoffregen Motorsports]

Flush that block! Probably install new freeze plugs too. The gunk in that water pump cavity is not a great sign for the freeze plugs.

 

Do you know how to replace freeze plugs?

[IvyCap]

6 minutes ago, Stoffregen Motorsports said:

Flush that block! Probably install new freeze plugs too. The gunk in that water pump cavity is not a great sign for the freeze plugs.

 

Do you know how to replace freeze plugs?

I've never knocked out freeze plugs or installed them. 

I bought the "How to rebuild your Nissan/Datsun OHC Engine" manual which does cover replacing freeze plugs.

Any suggestions for methods to flush the block? 

[Stoffregen Motorsports]

Removing them is easy. You knock one side into the block and then pull on the other side with a channel lock pliers.

 

Get yourself a wire cup brush and mount it in a drill, or better yet, an air grinder. Use this to clean the holes in the block before you install the new freeze plugs.

 

Installing them, you should use a piece of tubing or a socket of the same diameter so you knock the plug in from the inside diameter of the plug, not by hitting it on the rim of the plug.

 

Oh, and also, use thin bead bead of super weatherstrip adhesive on the plug before it goes in. This will help glue it into place.

[Stoffregen Motorsports]

Flush the block with a garden hose. If it is chunky, run a thick piece of wire inside the freeze plug cavities and poke around inside the block to loosen up any crap that may be stuck.