Another L20 question

Engine, Transmission and related drivetrain.
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Re: Another L20 question

Post by Button » 30 Dec 2016 13:32

Thank you for the great input guys. I was planning on rolling the dice and running it since as Mike said it came out of a running engine that was keeping the oil and coolant separate. The problem I ran into is that where it cracked part of the head surface of the block raised up a bit at the crack and the deck is out of spec flatness and I didn't want to do a full lower end rebuild so properly decking it is out of the question for this engine. If I was going to do a full rebuild I have a different block that seems in better condition but has other problems that are keeping it from being runnable as is.

For this block the rest of the top of the block is nice and flat(less then .002) so I thought about trying to grind/sand/flatten the spot at the crack but I wasn't sure how to do that without creating a divot there. A straight edge tetters totters over the high spot and leaves about .01 gap on either side depending upon which way the straight edge is leaning. Obviously the correct method is to get it properly decked but do you guys have any suggestions of how to approach doing a home job on flattening that spot? I have a gasket kit so I figure I don't have much to lose but time.

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Re: Another L20 question

Post by Chickenman » 31 Dec 2016 12:40

Cracks are a sign and stress relief and not an indication that it will get worse.? Sorry, Cracks are a sign of metal fatigue from repeated stress loads, stress risers or defective materials.Cracks will always spread. Planes used to fall out of the Sky far to often due to undetected cracks. They still do...

The coolant can leak up the bolt hole. Happens all the time on some engine designs. The bolts threads are not a perfect seal. Engines where the head bolts are drilled through to the water jacket have a factory thread sealant applied to the bolt threads to prevent coolant leaks.

ARP and other manufactures carry combination thread sealants and thread lubes made specifically for engines where head bolts or other fasteners are drilled through to the water passages. Quote from ARP.
Do the threads of the bolts or studs going into the block need lube?
Yes. On blind holes use a small amount of ARP Ultra-Torque lube on those threads. Additionally, if the studs protrude into a water jacket, you will need to clean the threads in the block to remove all coolant and oil residue. Apply a liberal amount of ARP thread sealer or a high temperature thread sealer.
That being said. For a Daily driver, you can probably get away with just applying some thread sealant to the head bolt or stud in that hole. Competition engine.. not so much. Nice welding job...

Datsun head bolt washers are Blanchard ground and will seal pretty darned good against coolant leaks. So that's a bonus for us.

Some other engine makes do not have as tight of tolerances. You don't ever want to work on a POS Ford 2.0 liter CVH engine. Ford didn't use enough sealant on the head bolt threads, which go right through to the water passage. Very common to find these engines with the head bolts rusted solid into the block and head. And being very long " Torque to Yield " bolts they tend to break in half. Lots of fun...

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Re: Another L20 question

Post by Button » 31 Dec 2016 13:18

That is good information to know Chickenman, thank you, if I do decide to use this block I will use the thread sealent like you suggested.

Anyone have any thoughts about flattening the highs pot on the block like I mentioned in my post above?

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Re: Another L20 question

Post by James » 31 Dec 2016 19:30

A light touch with a fine flat file could get you there I would think.
Finished is better than perfect......

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Re: Another L20 question

Post by Byron510 » 01 Jan 2017 09:56

James wrote:A light touch with a fine flat file could get you there I would think.
I'll add to James post; a light touch with the longest sharp, single cut file is you best bet when using a file.

Do not file towards the cylinder bore, try to stay lengthwise down the block. If you have a good sharp file, you'll see the high point right away.

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because the opposite never works.

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Re: Another L20 question

Post by Button » 01 Jan 2017 12:39

Thanks Byron, I had to look up what a single cut file was. I think I might have a good file for that but if not it will be a good excuse to but a new tool. I will keep you guys posted.

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Re: Another L20 question

Post by datzenmike » 01 Jan 2017 17:07

Cracks are over rated. Lots of running engines have them and have had them for years and will continue to have them for many years to come. Like some prostate cancers, you die of old age long before it gets you. They are not an omen of imminent doom. I've found four blocks that were cracked and you would never know it. Daily driving just doesn't stress them enough. They won't leak, they are L series, heavily over engineered and won't fall out of the sky. I doubt anyone here has had a crack in an L series (short of of a rod through the block) that was cause to pull it off the road.
"Nissan 'shit the bed' when they made these, plain and simple." McShagger510 on flattop SUs

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