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Old 05-19-2018, 01:32 AM   #1
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Default 1986 D21: fix the original motor or swap in something different?

As I mentioned in another thread; my 8 plug four banger has low compression on cylinders 2 & 3 (90PSI) but, 1 and 4 seem to be OK (180 PSI).

My Q being would I be better off overhauling the present engine or; can I (easily) swap in something else; another Four, V6 or V8? Note I'm not interested in having a hot rod although some more power; especially at freeway speeds, along with hill climbing ability; would help.

It's starting to seem I'd either be better off fixing my present engine or going with a 4 four cylinder Frontier motor vs 'crossbreeding'. As it stands; the FI was removed by a previous owner and, apparently I have a 720 carb which seems to work well to boot. If my head's junk; what 4 plug head would work, if any, assuming I work with what I already have? My present motor seems to have decent oil pressure and, makes no weird bottom end noises. If I go with the Frontier Four; I'd have to use the OBD II engine management/FI system and, I'm OK with that.

I have my flame retardant suit on so; have at it.
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Old 05-21-2018, 06:39 PM   #2
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Your options depend on how ambitious you are. If there are no other issues with your current setup, then fixing what you have seems easiest.
Swapping a newer 4 might be a good option, but it may also need the crank sensor that goes in the bell housing.
A v6 would require the matching transmission.
A v8 swap in a D21 is straight-up fab work. There is nothing easy about it unless it is something you are used to doing.
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Old 05-23-2018, 01:46 AM   #3
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Quote:
Originally Posted by Reserector View Post
Your options depend on how ambitious you are. If there are no other issues with your current setup, then fixing what you have seems easiest.
Swapping a newer 4 might be a good option, but it may also need the crank sensor that goes in the bell housing.
A v6 would require the matching transmission.
A v8 swap in a D21 is straight-up fab work. There is nothing easy about it unless it is something you are used to doing.
I'm leaning towards fixing my existing engine since it doesn't knock, smoke or use oil. It does run hot at times and, has been known to spit water/coolant out of the overflow tank; at least after climbing a long grade (10+ mile @ 6 percent) with it pinging away.

And I ordered a head gasket kit as well as the timing chain holder.
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Old 05-23-2018, 03:27 PM   #4
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Look into replacing the radiator with a v6 version. It is thicker and should solve your overheat problems, assuming that everything else is in good shape.

Pro tip: you can remove the intake manifold with almost everything on it. Disconnect harness connections and throttle cable.
remove the intake bolts at the ends, and on top that are fairly easy to reach. When you get to the studs under the middle, you only need to loosen the nuts. The manifold is slotted and will lift straight up off of those studs.
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Old 05-25-2018, 04:03 AM   #5
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Parts came in yesterday and; I yanked the head today.

Poor head gasket is munched between cylinders 2 and 3 plus, the head has some erosion in the same area; I dropped off the head at the machine shop and, will get it milled along with having the damaged area filled in, if needed. Block has some slight damage between the same two barrels but; since the motor doesn't smoke and/or use oil along with no low oil pressure issues; I'll wing it with just the repaired head.
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Old 06-05-2018, 02:14 AM   #6
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Head was relatively undamaged; no welding needed, it cleaned up. Block was slightly eroded by cylinders 2 & 3; I gambled on the 'meanest' JB Weld out there, let it set overnight then, sanded it flush with the deck.

Went to put head on and, dropped the #%$%**^ timing chain down; off came the front cover and, our lead mechanic was able to retrieve it and, got everything buttoned back up.

Short story; got it started, it idles like a new truck and, the driveability is a 1,000% better.

Tomorrow I'll change the oil and filter, etc.
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Old 06-05-2018, 04:12 PM   #7
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Happy ending.
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Old 06-06-2018, 06:39 PM   #8
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If the head was milled,you'll need a shim below the head gasket. I learned this the first time mine['86 1/2 4x4] blew the head gasket. On the advice of the machine shop guy,I used the copper sealant on both the shim and gasket and it's running well for now. I replaced the radiator and power washed the block,though no trash came out. I made a chain holder from a 1x2,8" long with a blunted point at one end and it worked well.
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Old 06-16-2018, 03:22 AM   #9
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Quote:
Originally Posted by Lha View Post
If the head was milled,you'll need a shim below the head gasket. I learned this the first time mine['86 1/2 4x4] blew the head gasket. On the advice of the machine shop guy,I used the copper sealant on both the shim and gasket and it's running well for now. I replaced the radiator and power washed the block,though no trash came out. I made a chain holder from a 1x2,8" long with a blunted point at one end and it worked well.
Oh boy; engine's all back together, so I'll think I'll let sleeping dogs lay. Note this D21 has alomst 250K on the clock. Odd; this this is the first time I heard about needing any sort of shim..........
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