671 Vibration Trouble

Sammy · September 25, 2006, 03:06:35 PM

I'd do a compression and leakdown test to all cylinders.
I would also remove the Jake brakes and run the engine.
I had a set of defective Jakes cause smoking and missfire symptoms, don't believe it's a very common condition, but worth checking.
Good luck.

guy 4905 · September 25, 2006, 05:21:39 PM

You indicate that this problem has been around for quite a while. You might try to get your mechanic to do a compression test. If by some chance somebody installed pistons or kits and got two cylinders with turbo pistons, that would give you lack of output on two cylinders, plus the different weight of the piston assemblies might give you the unbalance condition. Just a guess, but these weird things happen occasionally.
Guy 4905

GM0406 · September 29, 2006, 01:12:32 PM

Just to keep you all up to date, I just had a long conversation with Martin about this. They are going to look for their tool to do a compression test on the engine. I reminded him that I have noticed backfiring from the jakes when they are applied. I know jakes make a lot of noise, but this engine actually makes explosions or back firing when you activate the jakes. You can duplicate it by going back there and activating the jakes while letting it coast down from say 1500 rpm. I don't know if this could affect the operation of 2 and 5, but I asked them to check. I suspect that somehow these jakes are causing valves to remain open if this is related to the miss with the jakes off. Bill

GM0406 · September 30, 2006, 12:07:43 AM

Well they are going to do a compression test, and now that I put them onto the jakes, they will check them. Amazing about the turnbo pistons. Sure hope I don't have them. But that just might be it! Bill

mak · September 30, 2006, 04:34:14 PM

Had the same problem years ago when I operated 5 of the old 4104's. Turned out to be the fan blade, one of the blades was a little lose and shook at the higher RPM. I know you have check it, but that was the problem in mine, new fan blade, problem gone, $100 back then....
mak

GM0406 · October 05, 2006, 05:26:33 PM

Tom,

Currently I am trying to get hold of Vance Butler in San Diego who built this engine. I am hoping he can shed some light on what might be the problem. I don't think I am going to turbo this engine. I can jump in my '06 with an 8V71 TA. Believe me, that coach wasteth no time whatsoever and there are precious few coaches or trucks that can catch her. In fact I have to get in the fast lane on the passes around here to avoid being bogged down by people who routinely slow down in the left lane on a climb. It is as if they don't understand the principle of "crank her up"! No, the '04 is a very nice coach to relax and set the cruise control, watch the fuel mileage that is reasonable, and basically have less stress in the driver's seat and at the diesel pump. Meantime the 40' coaches can pass me on the way to the next diesel stop where they will have the priviledge of filling up first! Fuel still way too expensive for us here.

Bill T.

Bill T.

GM0406 · October 09, 2006, 09:03:41 AM

Just an update here. I started another topic as I thought we had a jake problem. The jakes have been checked and are not the cause of the vibration or miss. I have not heard the coach run yet, but Bay City DD shop tells me that the injectors got rid of the miss, but not the vibration which is pronounced at 1,400 RPM. They have found that there is 0.024 endplay in the crank. It should only be 0.014 max. They see the flywheel moving back and forth, but the rainout on the flywheel is in spec. Numa, the mechanic that is working on it, says we need to drop the pan and go in and replace the mains to avoid likely future damage. They will also check to see if there are any other problems when they have the pan off. If we still have a problem after this work is done, then the trans will have to come out for further checking.

Geoff · October 09, 2006, 12:53:10 PM

If the engine is out of balance after it was apart I would suspect the cam/balance shaft weights are incorrectly matched up. For your information, the crank uses thrust washers that are also available in oversizes in case the crank machined. I hate to say it but from the guessing game the shop is playing I suspect they aren't used to working on 2-stroke Detroits.

--Geoff
'82 RTS AZ

GM0406 · October 09, 2006, 06:30:54 PM

I understand that the thrust on this engine is one of the mains that must be worn. Is this correct? If so, it better be replaced. And that means removal of the pan. I understand that this may not be the cause of the vibration, but I think it is better to get the excess endplay out of the crank as long as they found it. So currently they have solved the miss, and now we are going for the second known, which is too much end play in the crank. They will also take a good look when the pan is off and check that all in there is tight. They will also install a spin on oil filter adaptor on this engine so I can use spin on filters from now on. I was going to have them pull the Frantz off that Geroge Thornhill installed, until we looked a little closer. I didn't realize that George had installed this filter to filter the oil scavenged from the blower before it returns to the pan. When I saw that, I told them to leave her be. No need to remove an important part of what is happening on this coach. There are no oil leaks from this engine, period! I can almost hear the cheering from here!! LOL! But this I am a witness of, that George conquered engine leaks. But, the transmission does leak a little as well as the two speed. Another day for that. First I would like to get the miss and vibration gone. My guess on the miss was an injector, and that proved right. The vibration is a little trickier. And they can even give a good mechanic reason to cringe. I really appreciate your input here and will keep all informed of the progress. When we solve the problems, I will report here for the benefit of all of you here. Thanks Again to all that have contributed here, Bill T.