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post #1 of 10 (permalink) Old 10-09-2008, 07:21 PM Thread Starter
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rebuilding diesel engines

Hey guys, Im an automotive student and Im fairly familiar with rebuilding gas engines but I would like to try my hand at rebuilding a diesel. Could someone tell me the major differences in rebuilding a diesel? Is it common practice to replace cylinder sleeves as opposed to boring the cylinders as in gas engines? Do these even have sleeved cylinders or are they integrated into the block? Im probably thinking 5.9 cummins. Do diesel rebulds usually include new pistons?
How about heads? are valve guides and seats basically the same? Thanks, Brian

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post #2 of 10 (permalink) Old 10-09-2008, 08:46 PM
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Well, to say it simply, their isnt alot of difference in rebuilding a gasser and a diesel. Only you are dealing with a front geartrain (not much different than a gassers timing chain/belt) for the cam and inj pump and accy's(ps pump,vac pump, compressor)

The smaller cummins's do not have sleeves, they are a parent bore block, like gassers, this includes the 5.9. You wont find alot of smaller diesels with wet sleeves, i know for one, john deere does make some, we have a 4045JD (4cyl 4.5L) thats wet sleeved but none of our 3.3/3.9/5.9 cummins's are.

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post #3 of 10 (permalink) Old 10-09-2008, 09:52 PM
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Subscribes....... Good info here. And good post!

Welcome to the forum Brian.

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post #4 of 10 (permalink) Old 10-09-2008, 10:38 PM
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Brian, Valve guides are where the stem of the valve rides in, valve seats are what the valve rests on to seal the combustion chamber.
As far as pistons go, they can usually be reused. Hone the cylinders and replace the rings.
All cumins B series engines are parent bore engines as stated above, however, there are over sized pistons available if the cylinders need bored.
If only one cylinder needs repaired, the block can be bored to accept a sleeve, then the sleeve bored to accept a standard bore piston, or whatever size the rest of the pistons are, then you only have to buy one piston. (belive me, they're pricey)
Hope this helps!
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post #5 of 10 (permalink) Old 10-10-2008, 06:20 PM Thread Starter
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Thanks guys. I have an engine overhaul class coming up and the 5.9 is a possible victim. Where can I get a rebuild kit for one? Any major differences between model years besides the switch to 24v? (what year was that anyways?)
Thanks, Brian
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post #6 of 10 (permalink) Old 10-10-2008, 06:31 PM
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98.5 is when they switched to the 24valve

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post #7 of 10 (permalink) Old 10-11-2008, 04:13 PM
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and the dreaded 53 block!


Also, while its torn apart, dont forget to take care of the KDP

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post #8 of 10 (permalink) Old 10-12-2008, 11:11 PM
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Most overhauls you will see will need minimal work on the wear surfaces unless the engine has been severely abused. Modern chemical engineering makes rings practically not wear, to the point that running dry often wipes out a crank and rod, not the bore.

The only real wear issues on a properly maintained diesel will be; valve seats and valves, carbon buildup on valve stems, and soft items such as valve seals etc.

The main difference with diesels is the accommodation of the compression ratio. On IDI engines that run 23:1 give or take, the valve job can SIGNIFICANTLY change the compression ratio. DI engines such as the Cummins are much more forgiving as they are 16:1 (etc engine) or 16.5:1 (eth engine) so valve depth plays much less of a role in compression ratio.

However, valve face protrusion is still a major concern and worth careful measurement if you replace valves, and ESPECIALLY if you replace seats. This is mainly for preventing piston/valve contact, but is worth careful note. When determining course of action on the head, the fact that it is a DI engine may sway heavily towards minimizing work on the head. The main problem with valve/seat wear is difficulty starting the engine cold, but DI engines are MUCH MUCH more forgiving of being out of spec. IDI engines can be a NIGHTMARE to start if the valves are excessively worn. Most engines allow about .015" of wear to give you an idea.

I'm not sure about the Cummins, but all the IDI diesels I have cracked had multiple head gasket thicknesses to match compression accordingly. They were all IDI's though, so the Cummins MAY just have one. I dunno. Incidentally none so far has needed a complete overhaul, and some were SEVERELY abused.

If you don't do the head, I would encourage you to still pull the valves and clean the carbon off the stem/face as this will improve performance/efficiency measureably. You may be tempted to lap the valves, but if you do, go light. It's pretty easy to take them out of spec.

To summarize, the main difference in a diesel overhaul is the care regarding the valves and head.

PS, before ordering parts, I would consider taking measurements. IE ring end gap, plastiguage all the journals, and measure valve depth. You may be surprised.

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post #9 of 10 (permalink) Old 10-14-2008, 06:34 PM Thread Starter
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thanks guys, good info. I will definately be going through all the journals, clearances, gaps, etc. for the purpose of the class. What is the KDP, IDI and DI?
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post #10 of 10 (permalink) Old 10-14-2008, 07:02 PM
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How about this question. Why are the connecting rod caps angled? The Powercroak 6ohno has this design also. I have heard two different reasons. One reason is so the rod can fit in the bore and the other reason is it somehow centers the stresses better.

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