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jdemaris
07-17-2006 19:13:59
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Re: diesel compression in reply to MF294-4, 07-16-2006 06:42:37
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Compression should test at around 400 PSI. It's normal for the first revolution to show a low reading, but it should then come right up. If it seems to build up slowly and not reach its peak until 6 or 10 revolutions, then you've got piston/cylinder wear problems. In regard to anyone simply blaming it on "rings", that's rediculous. There was a time when engines had soft cast-iron rings that would wear faster than the cylinder wall or piston grooves. But with todays modern engines - especially diesels - if the rings are bad, so will be the pistons and the cylinders. In the case of the turbo- 396 cube (6.5 liter), it uses Keystone triangle shaped rings which are more durable than the straight side conventional rings. If you've run the engine with the exhaust manifolds off, and the smoke is concentrated on certain cylinders - and not ALL the cylinders equally - then you've surely ready for a teardown. If they all smoke, but the engine starts and runs well, I'd do some further checking on the advance timing. If not advancing properly, it will smoke and skip - especially in a no-load situation. I'll assume you are sure the turbo is not pumping oil into the intake. You mentioned your 6.5 being a 94 with no emmissions and an electronic pump. I'm not sure what you mean by that. The electronic pump is PART of an emissions package - if you have electronic, then you have SOME emmissions controls. 93 I believe was the last year of the 6.5 turbo with mechancial pump for civilian use - unless a replacement engine was used. GM sold mechanical replacement engines into the late 90s. If it was my truck - I would not use the electronic pump. It was a awful setup and 1994 -95 were the worst and GM lost millions. Then it was updated to the 2nd generation pump and it was still bad - but better. At the end of 1997, GM came up with the 3rd generation pump which was finally somewhat reliable. In my mind, why bother? The fuel mileage is just as good if not better with the old mechancical pump, the old pump is MUCH more reliable, much cheaper to fix or replace - to me it's a no-brainer. I've got many GM diesels and love them. Not as powerful as my Ford/IH diesels, but always better on fuel mileage. My standard bragging unit was my 87 6.2 Suburban with 505,000 miles on it with NO tear-down. Well - it just blew up - with no warning. Going down the interstate at 80 MPH - running great, 80 PSI oil pressure, cool engine - and wham! - seized up so fast the fan belts flew off. I suspect the crankshaft broke in half - 6.2s and 6.5s sometimes do that at high miles. So - I'm now looking for a good used 6.5 with 100K miles or under. They are hard to find at a reasonable price. I would NOT buy a rebuild with a reground crank. I suspect 6.2s and 6.5s have a metal fatique problem with the crankshafts and that's why they sometimes snap in half after many miles. I don't see how regrinding a crankshaft is going to "unfatique" the metal. I've seen that some marine racing 6.5s have forged cranks - but the standard cranks are all cast-iron or nodular iron I believe.
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