TAZZJR
Member
- 67
- 99
- 18
- Location
- Baytown Texas
The motor of my m35a2 has developed a load hard knock. I have done about a week of testing to narrow down what could be the cause of the problem. I was able to drive the truck over an hour to get it home without the noise increasing in volume or rhythm. The knock is only once every four strokes and not twice every four strokes. The noise seems to come from the exhaust side of #3 cylinder.
I decided to check each injector by loosening the supply fule line and listening to the motor. I found that the knock goes away when I loosen the #3 cylinder injector supply line. As soon as I tighten the line and pressure returns the knock also returns. This can be done with a 90° turn of the wrench between not knocking and fuel spraying, and a closed fitting and the knock returning.
At this point I swapped #3 and #5 injector to see if the noise would follow the injector. The noise stayed in #3 cylinder and no additional noise was made. I swapped #3 and #5 injector again this time make 100% sure that I was actually swapping them and not making a stupid mistake. The result was the same.
Next I removed the valve cover and checked my rocker arms there was a noticable amount of play in the rocker arms of #3 cylinder. I adjusted all of the rocker arms. There was no change in the noise. I also inspected the flow of oil up and through the rocker arms. There was good flow with no problems the the bearings.
Next I checked the push rods and lifters of #3 cylinder. The push rods were true and did not seem to suffer from impact. The lifter of exhaust valve came up and out of its hole while I was inspecting the push rod. I was able to turn the lift of the exhaust valve over and take pictures of it and a few of the cam with the valve cover off. I would not suggest anyone do this intentionally. To get the lifter back in place with out taking the motor apart at this point is a nerve wracking experience and requires an extendable magnetic on flexible metal hose, a cut of coat hanger wire with a 1/2 in 90° turn in the end, a large flat head screw driver to prevent the lifter from jumping to the other cylinders, a flashlight and to lay on your stomach ontop of the truck for a few hours.
After a week of work I put the truck 100% back together, prayed, and turned it on. The motor still ran, the knock was still present.
My only two ideas of what it could be now is a damaged valve or a blown head gasket.
I believe I need to do a pressure test on it now. I'm not sure how to go about this.
Any advice would be appreciated.
I decided to check each injector by loosening the supply fule line and listening to the motor. I found that the knock goes away when I loosen the #3 cylinder injector supply line. As soon as I tighten the line and pressure returns the knock also returns. This can be done with a 90° turn of the wrench between not knocking and fuel spraying, and a closed fitting and the knock returning.
At this point I swapped #3 and #5 injector to see if the noise would follow the injector. The noise stayed in #3 cylinder and no additional noise was made. I swapped #3 and #5 injector again this time make 100% sure that I was actually swapping them and not making a stupid mistake. The result was the same.
Next I removed the valve cover and checked my rocker arms there was a noticable amount of play in the rocker arms of #3 cylinder. I adjusted all of the rocker arms. There was no change in the noise. I also inspected the flow of oil up and through the rocker arms. There was good flow with no problems the the bearings.
Next I checked the push rods and lifters of #3 cylinder. The push rods were true and did not seem to suffer from impact. The lifter of exhaust valve came up and out of its hole while I was inspecting the push rod. I was able to turn the lift of the exhaust valve over and take pictures of it and a few of the cam with the valve cover off. I would not suggest anyone do this intentionally. To get the lifter back in place with out taking the motor apart at this point is a nerve wracking experience and requires an extendable magnetic on flexible metal hose, a cut of coat hanger wire with a 1/2 in 90° turn in the end, a large flat head screw driver to prevent the lifter from jumping to the other cylinders, a flashlight and to lay on your stomach ontop of the truck for a few hours.
After a week of work I put the truck 100% back together, prayed, and turned it on. The motor still ran, the knock was still present.
My only two ideas of what it could be now is a damaged valve or a blown head gasket.
I believe I need to do a pressure test on it now. I'm not sure how to go about this.
Any advice would be appreciated.
