How To: Repair a Cracked K-Series Engine Block (At Oil Sender)

Oh, Come On

I was putting in an oil pressure sender, and the engine block casting cracked. The threads in the back of the block that hold the oil pressure sender are 1/8" British Standard Pipe Thread (BSPT), so they're tapered. What happened to cause this was probably some oil being left on the threads, and it affected the reading on my torque wrench. By the time I reached 13 ft-lbs, the sender unit was far enough into the threads to crack the casting off the block. Anyway, on to solutions.

The Carnage

There's a couple ways to go about fixing this fortunately. If this happened to you, you need to choose what makes the most sense for you depending on the crack severity and location.

Possible Solutions

1. Grind off the casting, re-tap the hole, and plug the block. Install an oil filter sandwich plate and get oil pressure from there.
2. Remove the engine and weld the block back together and re-tap the threads.
3. Remove the engine and swap the block for another K20 block, or a K24 block from the junkyard or eBay.

If you need to do things to the engine out of the car anyway, having it welded, or you want to make more power and need an excuse to do it, K24 swapping or K24 frankenstein-ing your K20 might be a good option. If you have a Type-S, you might need to get the transmission out anyway to fix your gears and synchros if they're grinding or popping out. If you have a base model and K-Pro or K-Tuner, you might want to swap your engine for a K24. Think of it as motivation to do what you were already planning to do.

If you don't need to mess around in your engine, or want to make it as simple as possible, you'll want option #1. This is what I chose, and what I'll be teaching you how to do. 

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Tools Required

• 3/8" 16NC Tap
• Ratcheting Tap Wrench
• 1" Stainless Steel Hex Socket Head Cap Screw
• HondaBond OR Permatex Grey Silicone Gasket Sealer
• Q-Tips
• Grease
• Right Angle Mini Die Grinder and Air Compressor OR Electric Right Angle Mini Die Grinder
• Sanding Discs
• Dremel (Optional, Read Below)
• Metal Cutting Discs (Optional, Read Below)
• Isopropyl Alcohol
• Shop Towels
• Torque Wrench
• Fender Washer 7/16" ID, 1 1/4" OD Stainless Steel
• 5W-30 Oil (6 Quarts)
• K&N Oil Filter
• Oil Drain Crush Washer

                   

Instructions

1. I removed the front strut tower brace, and the Variable Valve Timing (VVT) solenoid so I could see better. I would not suggest skipping this step. When you disconnect the VVT solenoid, there shouldn't be a lot of oil that comes out; maybe a couple drips at most. 

Removing the Strut Tower Brace and VVT Solenoid Clear Up Your Workspace

Remove the 3 Bolts in the Front of the VVT Solenoid, and Remove The 2 Electrical Plugs To Remove the Assembly. They are 10mm.

2. I cleaned the VVT solenoid mounting surface with a shop towel and isopropyl alcohol and put duct tape over it to avoid accidentally hitting it with the dremel or die grinder and ruining the sealing surface since it's slightly above the oil pressure sender hole.

NOTE: Personally, I didn't have a die grinder until later in this project, so I used a Dremel and metal cutting disc to slowly "sand down" the majority of the damaged block area. For most people, I wouldn't suggest this since it can leave an uneven surface that you have to smooth later, and trying to sand a non-flat surface flat in a location you can't see very well is not very fun.

I Tried to Keep the Surface Even, But it Was Difficult In Such a Tight Space Without a Die Grinder

If you're confident enough to try to fix this and you have enough experience under your belt, make the investment and get either the electric or air mini angle die grinder and skip this step. It allows sanding this tiny area to be super easy and takes a lot of the guess work out of a potentially very difficult repair.

You Can Sorta See Here the Curve Introduced by the Dremel; I Had to Take This Out Patiently Later

3. I picked up a die grinder, and some sanding discs to get a flat surface on my engine block that I can tighten a bolt and washer up against. I only used 2 60-grit sanding discs.

This is my Mini Angle Die Grinder; I Removed the Safety Trigger Guard, and it Helped Comfort a Lot

NOTE: My air compressor is not huge, and the weather was 93 degrees Farenheit outside. As you can imagine, it was getting very hot with continuous use of the air die grinder. I cooled it off when it was running by getting a friend to spray water out of a squirt bottle onto the heatsink area. The water evaporates on contact and is extremely effective at dispersing heat and keeping your air compressor healthier.

You Can See the Surface is MUCH More Uniform Around the Hole, Post-Die Grinder

4. After the surface was flat around the hole with enough room for a washer to sit flush against, I brought out my 3/8" 16NC tap and started the slow process of tapping the block. I chose this size and thread because 3/8" fits the hole and cast aluminum generally takes course threads more reliably than fine threads. I used a general purpose grease to capture the metal chips. Once the tap is started in the hole and going in straight, bring the tap back out and clean the metal shavings off. Regrease the tap, and continue making progress slowly. Take your time, and focus on it going in straight; this is imperative to making sure it seals and threads possibly.

It Doesn't Look Straight in this Picture, But I Promise It's Just the Angle. The Ratcheting Function Made All of This Possible.

To tap this hole, you'll have to apply significant pressure on the tap wrench while holding it straight and level. The ratcheting tap wrench I suggested makes this possible. The ones that come in tap sets are usually garbage and the tap will fall out of them. (Trust me I tried, it sucked.)

Max Tap Depth For Me Was A Tiny Bit More Than An Inch. I Used 2 Washers to Be Safe.

The hole you'll be putting the tap into is decently long. If you measure from an unbroken K20 block, there's about 2" of room to tap into. Considering we broke off part of the block, there's less room in there. Just keep in mind not to go too far. If you do, it probably won't go through the wall, but you don't want to try.

NOTE: You can feel how far you are from the end by sticking a screwdriver down into the hole, and marking it with a permanent marker where it exits the block. Then you can tap to just before this depth. Just make sure you can fully insert the bolt without bottoming out.

5. Now that the hole was tapped, I cleaned every bit of grease, metal chips, and oil off the threads. Yep, this is the cleaning step. I used general purpose grease on a bunch of Q-tips and swabbed the entire hole's internal area until I stopped seeing aluminum chips and dust. If it takes all day, it's worth it to protect your engine from possible damage.

6. After you stop seeing metal chips and dust, put isopropyl alcohol on some more Q-tips and wipe out the inside of the hole until you don't see anymore grease. Grease can stop the sealant we're using from curing properly and creating a good seal. It might feel like it takes forever, but it's really important, again.

When you're done, use a shop towel with isopropyl alcohol to wipe off the general area around the hole.

7. When the threads are completely clean, open your HondaBond or Permatex Grey Silicone Sealant and spread a coat of it onto the threads of the bolt. After applying, put on the washer and tighten it into the hole you tapped.

Put in a bolt and washer with some Hondabond, and tighten it with a hex key. I used an 8mm hex key socket on my bolt, and turned it until it was tight against the washer. Keep in mind you're tightening into a cast aluminum block. I hand tightened the bolt until it felt tight, and didn't force it further. If you're the measuring type, don't tighten it beyond 13 ft-lbs with your torque wrench.

If you're worried about the fastener coming out due to vibrations, you can also use a lock washer. I'm not too worried about it since it's tightened in at the factory torque spec, and HondaBond can absorb some vibrations. I'll keep an eye on it though.

It's Finally in There! As I Said, I Used 2 Washers To Spread Force and Prevent Bottoming Out

8. Let the sealant dry for 24 hours before you start up the car. Otherwise you'll just blow it out the hole along with the contents of your oil pan at 13 PSI when you start the car. Letting it dry for longer can't hurt if you can keep yourself busy with something else.

9. If you have K-Pro, turn off oil pressure sender input. Alternatively, you can install an oil filter sandwich plate and attach the sender to that location if you don't have K-Pro. (Article on this incoming)

Uncheck This Box

10. Drive a couple miles, and then come back home and change your oil and oil filter. Also remove your VVT solenoid and check the filter screen for aluminum chips. Most should be sent through your oil filter though, since it's right next to the oil pressure sender location. I would also do your next oil change sooner than usual just so you don't have any of the stray pieces that loosen up as you hit VTEC become a problem. I included some cheap Amazon Basics oil, a great quality oil filter, and some fresh crush washers in my parts list. Despite being cheap, the oil got good reviews, and we need the stock oil weight combined with a strong filter to ensure no aluminum pieces get sucked into anything important. You can run this oil for 2,500 miles or less just to be careful, and then swap it out with what you normally put in there. After this process and the abbreviated oil changes, your engine should be nice and clean inside. Don't forget to replace your oil drain crush washer to prevent leaks!

Check the Filter, Labeled "B", for Leftover Aluminum Chips

That's about it! I sincerly hope it works out for you. It can be a little heartbreaking when you do something that feels silly like cracking your block in this way, but at least there's a way out of it. If you made a mistake with the tap and messed up the threading, you can either drill the hole out more and try to thread in a bigger size, or take it as a sign to get another block and do some maintenance while you're at it. Cars are challenging sometimes, but they usually teach you something about yourself.

If you're interested in hearing my how to properly choose an oil sender replacement and install it without cracking your engine block, that will be out soon.

FOLLOW UP: I have since finished my repair on my own engine. I stress tested it, and have been daily driving since the repair, and I'm happy to report everything is operating as it should. No leaks, no check engine lights, and smooth sailing.

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