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1987 F350 Crew Cab 4x4 7.3 IDI Turbo ZF5
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Discussion Starter · #1 ·
Ok, so the back story - I bought an '87 crew cab 4x2 ZF-5 DRW dually a year or so ago.

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The 6.9 was seized; had water sitting in the cylinders and would have needed sleeves.

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Bought a 7.3 IDI-T non-running for $1000. Disassembled it to find the block was .040. Junked the block and kept everything else.

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Bought a running low mile (30k IIRC) '88 F350 4x4 plow truck. Falling apart from rust, but had a good running NA 7.3 that I yanked. Sold the carcass for $500.

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Converted the project truck to 4x4 using Sky's Offroad kit and a king pin Dana 60.

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Starting on 7.3 build. Figure I'll use turbo rods, standard bore turbo pistons (need a set of these), aftermarket camshaft, head studs, aftermarket valve springs, upgraded IP and injectors, as well as a new or rebuilt/upgraded turbo. Not going crazy, and don't plan to run an intercooler.

I'll be doing videos of everything on my YouTube channel but I plan to post details here, too. https://www.youtube.com/@THEBULLETPROOFGARAGE/videos
 

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1987 F350 Crew Cab 4x4 7.3 IDI Turbo ZF5
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Discussion Starter · #3 ·
After a good start, things went sideways. I have a crack in the valve seat and between two valves in one chamber on one head. This head is junk right?

FYI - the first pic is magnaflux; second and third are dye penetrant.

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1987 F350 Crew Cab 4x4 7.3 IDI Turbo ZF5
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Discussion Starter · #4 ·
From there, I went to the 7.3 IDI heads from a 1994 turbo engine to see if they were good.

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No cracks in the heads, but all pre-cups have multiple cracks, some past the fire ring. Still haven't found a source for new pre-cups so this could be problematic.

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The '94 heads are not warped, but the driver's side head is right at .002". Figure since it's less than .003" I'm good, but I haven't found the specific spec for an IDI.
 

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👍 Enjoying the project, looking forward to the rest of the build.
 
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It's good to see someone with the financial wherewithal and the time and skill set to rebuild one of these old trucks. Most (myself included) just run them until they fall completely apart. I'm trying to hang on to the one I have now to try a complete rebuild after I finally retire...provided I'm still healthy enough. That time is getting close now. A hint, head warpage depends on the thickness of the gasket you use, but I wouldn't go over .003" either.
 

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1987 F350 Crew Cab 4x4 7.3 IDI Turbo ZF5
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30 Posts
Discussion Starter · #10 ·
It's good to see someone with the financial wherewithal and the time and skill set to rebuild one of these old trucks. Most (myself included) just run them until they fall completely apart. I'm trying to hang on to the one I have now to try a complete rebuild after I finally retire...provided I'm still healthy enough. That time is getting close now. A hint, head warpage depends on the thickness of the gasket you use, but I wouldn't go over .003" either.
Well, I wish I had more financial wherewithal, more time, and more skill, but I'm still plugging away! Thanks, Scott
 

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The cracked seat has to be repalaced but cracks between the seats are one of those things that can be there for hundreds of thousands of miles but bug the S**t out of you once you see them. If you have a good machine shop that has been around a while they would be a great resource to tell you how tolerant these are for cracks. I pulled one apart years ago that I had turbo'd and it ran hot a lot under hard pulls (the fix for that was cutting a 4 x 16 hole in front bumper to mimic the opening they put in 1993.5 only I did it 1992). I had the cup cracks and one crack on each head that were small and the two sides of the crack had no vertical difference. Machine shop said no problem to either as they were on those heads and I put it back together and I sold it to a friend and it got 100K hard miles by him before he sold it with no issues.
 
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1987 F350 Crew Cab 4x4 7.3 IDI Turbo ZF5
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Discussion Starter · #13 ·
The cracked seat has to be repalaced but cracks between the seats are one of those things that can be there for hundreds of thousands of miles but bug the S**t out of you once you see them. If you have a good machine shop that has been around a while they would be a great resource to tell you how tolerant these are for cracks. I pulled one apart years ago that I had turbo'd and it ran hot a lot under hard pulls (the fix for that was cutting a 4 x 16 hole in front bumper to mimic the opening they put in 1993.5 only I did it 1992). I had the cup cracks and one crack on each head that were small and the two sides of the crack had no vertical difference. Machine shop said no problem to either as they were on those heads and I put it back together and I sold it to a friend and it got 100K hard miles by him before he sold it with no issues.
Excellent information! First-hand experience is always very helpful.

I do have a local machine shop that I trust; I'll plan to bring them by.
 

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1987 F350 Crew Cab 4x4 7.3 IDI Turbo ZF5
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Discussion Starter · #16 ·
Checked the valves today to see if the stems were still within spec. Measured at top of valve (area where it doesn't enter valve guide) and then measured 1/3 down, and then 2/3 down the stem (areas where it travels in the valve guide). All valves were within spec, I believe, with no more than .001" variance on each valve.

All the 1988 NA 7.3 valves were .371: with one exception that was .372" for two measurements. Pretty sure this engine was never rebuilt.

All the 1994 7.3 turbo valves were .386". This engine had been rebuilt, so the rebuilder must have found the valve guides to be a bit loose, so they ordered .015 oversize valves and honed out the guides a bit.

I haven't checked the guides yet, but my guess is that the guides on the '94 heads are a bit tight because some of the '94 valves are showing wear on the stem and several of them were difficult to remove from the heads.

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1987 F350 Crew Cab 4x4 7.3 IDI Turbo ZF5
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Discussion Starter · #17 ·
Measured guides this weekend with small hole/split ball gauge and a mic.

The '88 NA heads are pretty damn good - all in the .0022" range, give or take. The factory spec was .0021" or so and max allowed is .0055" so I'm nowhere near that. Too bad one of the heads is cracked in between the valves; even if it passes a pressure test, I'd be nervous about using these.

The '94 turbo heads are another story. Most of the exhaust valves had some galling, and after checking clearances, I could see why -- some were as tight as .0005"! If I'm going to use these - and it looks like I am - the guides will need to be honed out (.002" on the intake and .003" on the exhaust?) and it will need 8 new pre-cups and probably all new valves, too.

I can pop out the pre-cups and install some new ones, but I'm going to leave the valve honing to a pro. I'd like to get a Sunnen valve honing setup but it's not in the budget at this point.

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1987 F350 Crew Cab 4x4 7.3 IDI Turbo ZF5
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Discussion Starter · #18 ·
Ok, just got off the phone with Justin at R&D IDI. When I told him what I wanted to do, he recommended an RD2-90 pump, the Stage 1 drop in turbo, Stage 1 camshaft, and some Stage 1 injectors. That's about $3k in parts, but I was expecting that. He recommended the turbo pistons (Mahle $750/set, can add ceramic coating on the top for $275) but he said only .020 and .030 were available right now. I need to call Mahle tomorrow to see if they have any standard bore available or in the queue. I'll also need a set of head studs; he has ARP stud kits for $585. Justin runs factory pistons and compression ratio up to 400 hp/800 ft lbs.

Justin told me to steer clear of the head that I have that's cracked between the valves, and also mentioned that the pre-cups on the market weren't the highest quality, so run the cracked ones (even if cracked past the fire ring) or harvest the pre-cups off the '88 NA head that's cracked and install these in the '94 heads. For valves, I need to source exhaust valves with the stellite face.

We talked about intercoolers and he mentioned that I should be fine if I keep an eye on EGTs and don't tow heavy.

Justin mentioned the cranks were different turbo and NA - same forging but turbo had more weight added to balance. Apparently I can check the casting number to verify that the 1994 crank that I have is the turbo version.

The good news is that I can expect to make 250 hp and 550 ft/lbs at the wheels - manual trans - with the above setup. Hell, I would have been happy with 500 at the crank, so 550 at the wheels is mighty fine by me.
 

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1987 F350 Crew Cab 4x4 7.3 IDI Turbo ZF5
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Discussion Starter · #19 · (Edited)
Some good news and some bad news today - bad news is that the crank from the 1994 IDI turbo engine that I disassembled is not the correct one for the turbocharged engine. It's a 1805420C1 (regular 6.9/7.3 crank) not the 1805420C2 turbo crank, which is balanced differently because of the heavier rods and different pistons.

I could try to source a C2 crank and proceed but I'm not hopeful that I'll find one. I could also buy new turbo pistons and then have everything balanced, which would set me back $350 or so + cost of mallory. It could easily end up costing $500.

However, if stayed with the stock NA bottom end, I could sell my turbo rods, use my existing pistons (30k original miles on the block), and wouldn't have to have anything balanced. That would be significant cost savings.

Obviously the turbo rods and pistons would be preferable, but there are plenty of these engines out there running turbos on stock bottom ends, and I keep the boost and EGTs under control, I should be fine.
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