Inspection is Probably The Most Important Aspect of Our Cracked Cylinder Head Repairs
Visual Inspection: It sounds silly but sometimes it can tell you a lot. The biggest problem we run into in cracked cylinder head repair is when the engine has been replaced with an engine from a different year. Doesn’t mean it won’t run right but parts can be different (torque specs etc).
Thickness of the head: Who cares? We Do! If the head is below minimum before we start, this can be serious (particularly for overhead cam heads, cam timing, not enough belt or chain adjustment, valve to piston clearance to name a few).
Is the cylinder head warped? Goes back to minimum thickness. If it’s out .025″ and it is .005″ from minimum thickness, it will be under after we’re done. We can straighten it (we made our own plates 25 years ago, long before many people thought of it) but a less costly alternative is a “shim”. We always check before we do anything for availability. There are more aspects to that, if you’d like go to our cylinder head repair blog, we’ll discuss them.
Disassemble valves, springs, cams, rockers, lifters, if applicable; remove freeze plugs and anything else that is appropriate.
Cylinder Head Pressure Test: Another critical area of cracked cylinder head repair.
There are various methods of pressure testing. We feel that sealing the cylinder head, pressurizing it and submerging it under water is the best method. Even if you can’t see the leak, you always see the bubbles.
The following is a picture of a head that was brought to us after being removed from the engine 3 times. YES, 3 TIMES!!!
It was removed originally when it overheated and twice more after supposedly being pressure tested each time. Each time it was re-installed, it had water in the oil. The cracks are outlined with black marker.
This cylinder head isn’t cracked; it’s almost in 2 pieces. I don’t know how the head was tested but this is a bad result for you. This poor girl’s car has been in the shop for 2 months. We found this an hour and a half after it hit our door.
Cleaning: We use a variety of methods but since aluminum cylinder heads are the majority of the heads we cover, we’ll discuss that. We use a 2 step treatment consisting of spray wash and ultrasonic cleaning. We knock the heavy stuff off in the spray and finish clean with Ultrasonic. Ultrasonic is good because it gets the inside as well as the outside clean. The following is a before and after view of a pair of Mercedes Benz V-6 cylinder heads. These were done as a test so there was no tear down, nor pre-wash, both of which we do automatically every time.
This is the result after 20 minutes in the Ultrasonic. This has greatly improved not only the quality, but the speed at which we can complete the work and get you, or your customer, back on the road.
Valve Grinding: Not a big deal, but an important one. We use a grinder accurate to .0005″. Again it’s a small point but that’s why we’re able to offer our Lifetime Warranty* on all reconditioned and new cylinder heads.
Valve Seat Finishing: I don’t want to sit here and point out the pros and cons of cutting the seats versus grinding the seats. There are too many people doing that already. The fact is both have their strong and weak points; that’s why we use both.
The advantage to cutting the seat is that you can accurately put the seat angle anywhere on the valve you want. You also can control the depth to within thousandths of an inch.
By using a narrow finish seat width cutter, we can stop .005 to .010″ short of our assembled height and finish with stones.
Seat grinding stones come in all shapes, sizes and varieties. By getting the seats so close with our 3 angle cutter, we can use very fine seat finishing stones to make the perfect seat. Best of both worlds!
Resurfacing: According to “Fel-Pro Gaskets Tec Tip, Understanding Multi-layer Steel (MLS) head Gaskets”:
“Most MLS require a surface smoother than 40Ra… Regardless of the brand of MLS gasket chosen, for the gasket to seal properly, the finish on the head and block must be flatter and smoother than what has traditionally been required for composite gaskets.”
That being said, the following is a comparison between what it should not be and what it should. The first cylinder head is one we received after it had been to a shop, put back on the car, overheated again but the 2nd time it cracked the head. Below is what it shouldn’t be.
This was surfaced on a stationary grindstone surfacer I haven’t seen in 25 years. It’s not accurate and produced a Ra finish between 62 and 96Ra. The MLS head gasket had no chance. The picture below is what it should be.
This was done on a variable speed CBN (cubic boron nitride) surfacer. The Ra is between 22 and 27Ra. We can get it as fine as 12 to 15Ra, crankshaft smooth. It can also be adjusted to produce a rougher finish for composite gaskets.
In either case, having the right equipment and people to operate them will make your life so much simpler. Whether you use us or someone else, I hope this helps.
Assembly: Right tool for the right job!