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Allow me to share my expensive and frustrating lessons learned after having to fix the mistakes made by a commercial engine re-builder. I purchased a 6VD1 long block not long ago and after a mere 6,800 it blew a head gasket and hydraulically locked cylinder #3. After removing the engine from the vehicle, I began the tear-down and wanted to determine the cause of the failure. I carefully measured the EXISTING torque on all the head bolts of both banks with a precision strain-gauge torque wrench and found that the majority of the bolts were way below the specified torque value of 47 Ft. Lb. for both the M11x1.5 and the M8x1.25 bolts. Some bolts were as low as FIVE Ft. Lb.!! These are not TTY (Torque to Yield bolts).
I was flaming mad that the engine builder could not get these critical fasteners installed correctly and that I was having to fix their sloppy workmanship. However, I soon found out perhaps one important clue why the assembly failed. The company I bought the long block from sent me a new set of gaskets and new head bolts. As with a lot of things these days, it was all made in China.
After making sure there were no bent connecting rods and/or valves (since there was a hydraulic lock up) I proceeded to reassemble the heads to the engine block. It is important to note here that my Isuzu factory manual clearly states to (a) use new head bolts and (b) do not oil the threads of the bolts when installing them. So like any good mechanic, I followed the book verbatim.... and that's when the problems started.
After making sure that both the block decks on both banks were spotless, wiped down with denatured alcohol and compressed air dried, I installed the head gaskets, head bolts and proceeded to start my torque up procedure. After getting to less than half of the required 47 Ft. Lb I started experiencing what's called "Thread Seizing" or "Cold Welding". This is where the fasteners hang-up and stick, then suddenly break free only to repeat this sticking as the bolts keep tightening. The reality is that after one or two of these sticking events, you have no freaking idea what the torque value is on your bolt. The torque wrench might say 47 Ft. Lb. but that's only because the bolt is frozen or stuck in position due to "cold welding". The bolt is actually well below that shown value.
I was not about to have another head gasket failure so I took the whole assembly apart to find out what was going on. Of course, once you've clamped down a head gasket, you can't re-use it. So I purchased a set of Felpro head gaskets locally....And that's when I got yet another lesson in how Chinese made stuff is often such a lower quality than what's made elsewhere. The Felpro head gaskets were made in Germany and the level of difference in quality compared to the Chinese gaskets was astounding! I was actually glad I had to take the heads off.
So once again, I cleaned and started to reassemble the heads to the block, following the Isuzu factory manual's instructions. And once again I encountered the "thread seizing" issue after being well under the final torque of 47 Ft. Lb. The only logical solution was to say to hell with the Isuzu instructions in this case and oil both the bolt threads and the bolt heads (which have attached hardened flat washers) with 10W-30. Lo and behold.... every bolt goes to full torque with no seizing or cold welding! I realized that the engine builder I bought this from probably had the same issues but didn't attempt to correct the problem and simply let this engine go out to a customer. That fact together with a low quality head gasket pretty much guaranteed that this engine was going to have a failure.
The engine has been successfully running now for ~ 100 miles with no issues. So the lessons I learned and wanted to pass along is that (a) There are often huge differences in quality based on who makes a part and where it's made. So when it comes to critical items like head gaskets, etc. buy the highest quality parts you can afford. And (b) the Isuzu factory information, while certainly your best resource for reliable information .... sometimes leads you astray and it's up the mechanic to be the final quality "inspector" to be sure the job is done correctly.
I was flaming mad that the engine builder could not get these critical fasteners installed correctly and that I was having to fix their sloppy workmanship. However, I soon found out perhaps one important clue why the assembly failed. The company I bought the long block from sent me a new set of gaskets and new head bolts. As with a lot of things these days, it was all made in China.
After making sure there were no bent connecting rods and/or valves (since there was a hydraulic lock up) I proceeded to reassemble the heads to the engine block. It is important to note here that my Isuzu factory manual clearly states to (a) use new head bolts and (b) do not oil the threads of the bolts when installing them. So like any good mechanic, I followed the book verbatim.... and that's when the problems started.
After making sure that both the block decks on both banks were spotless, wiped down with denatured alcohol and compressed air dried, I installed the head gaskets, head bolts and proceeded to start my torque up procedure. After getting to less than half of the required 47 Ft. Lb I started experiencing what's called "Thread Seizing" or "Cold Welding". This is where the fasteners hang-up and stick, then suddenly break free only to repeat this sticking as the bolts keep tightening. The reality is that after one or two of these sticking events, you have no freaking idea what the torque value is on your bolt. The torque wrench might say 47 Ft. Lb. but that's only because the bolt is frozen or stuck in position due to "cold welding". The bolt is actually well below that shown value.
I was not about to have another head gasket failure so I took the whole assembly apart to find out what was going on. Of course, once you've clamped down a head gasket, you can't re-use it. So I purchased a set of Felpro head gaskets locally....And that's when I got yet another lesson in how Chinese made stuff is often such a lower quality than what's made elsewhere. The Felpro head gaskets were made in Germany and the level of difference in quality compared to the Chinese gaskets was astounding! I was actually glad I had to take the heads off.
So once again, I cleaned and started to reassemble the heads to the block, following the Isuzu factory manual's instructions. And once again I encountered the "thread seizing" issue after being well under the final torque of 47 Ft. Lb. The only logical solution was to say to hell with the Isuzu instructions in this case and oil both the bolt threads and the bolt heads (which have attached hardened flat washers) with 10W-30. Lo and behold.... every bolt goes to full torque with no seizing or cold welding! I realized that the engine builder I bought this from probably had the same issues but didn't attempt to correct the problem and simply let this engine go out to a customer. That fact together with a low quality head gasket pretty much guaranteed that this engine was going to have a failure.
The engine has been successfully running now for ~ 100 miles with no issues. So the lessons I learned and wanted to pass along is that (a) There are often huge differences in quality based on who makes a part and where it's made. So when it comes to critical items like head gaskets, etc. buy the highest quality parts you can afford. And (b) the Isuzu factory information, while certainly your best resource for reliable information .... sometimes leads you astray and it's up the mechanic to be the final quality "inspector" to be sure the job is done correctly.
