85 720 4x4 head gasket & valve questions

1980-1986 Datsun 720 forums. All 720-specific topics and discussion can be found here.
TheSurlyBadger
Posts: 3
Joined: Sun May 22, 2022 8:19 pm
Car: 1985 Nissan 720 King Cab 4x4

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Hello all, I *did* do some searching before starting this post!

I picked up a '85 720 last fall, and just started digging into it. It ran when I picked it up, drive it home. Rather gutless (max about 45mph), pretty significant engine vibration on start, and ran pretty hot (even with topped off radiator) - lots of cracked vacuum lines, very poorly tuned carb (previous owner had no idea what he was doing and cranked on various knobs randomly) - so there are a lot of opportunities for improvement.

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I did some digging and came to the conclusion the head gasket was *likely* blown, but failed to do a compression test before tearing in - I definitely should have done that first, and would in retrospect.

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Regardless, I pulled the head off and snapped some photos. It appears that #4 is the problem child here, but I'm not having much luck identifying exactly what is going on in that cylinder, specifically the build up on the exhaust valve. I _think_ from what I can find via the google is that I'm burning some coolant in that cylinder, but thought I'd post a few photos in here in case someone with more experience that I do knows exactly whats going on.

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Next up, I have a machine shop where I'll be dropping the head off to machine it, do new valves, etc, as I don't have the equipment necessary - and I definitely trust this shop more than my garage.

FWIW the #2 and #3 cylinder look really good from what I can see, I'm reticent to spin the crank to check #1 and #4 without pulling the whole front off and dealing with the timing chain - any tricks there that I don't know about? Thanks!

-Badger


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VStar650CL
Technical Expert
Posts: 8962
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

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That problem in #4 looks more like oil than coolant, coolant will usually blow all the carbon off the valves and crown and leave everything shiny.

TheSurlyBadger
Posts: 3
Joined: Sun May 22, 2022 8:19 pm
Car: 1985 Nissan 720 King Cab 4x4

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Thanks VStar650CL! (My second bike was a VStar 650!)

I wasn't sure, thanks for weighing in on what could be causing that odd buildup on #4

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VStar650CL
Technical Expert
Posts: 8962
Joined: Thu Nov 12, 2020 1:25 pm
Car: 2013 Nissan Altima 2.5 SL
2004 Nissan Altima 2.5 S

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Happy to help. :dblthumb:

TheSurlyBadger
Posts: 3
Joined: Sun May 22, 2022 8:19 pm
Car: 1985 Nissan 720 King Cab 4x4

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Does anyone have a trick to rotate the crankshaft to check all 4 cylinder walls w/o pulling the front off and re-doing the timing chain?


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