css1634 Posted April 11, 2015 Report Share Posted April 11, 2015 I have a 77 620 that Jumped time, it warped valves, not yet sure how many. I have been looking around for replacements as i am going to pull head this week. Seeking ideas of best place to get them Quote Link to comment
datzenmike Posted April 12, 2015 Report Share Posted April 12, 2015 Very unlikely this has happened. Only seen this when a head has been removed and the cam turned off of TDC position then torqued down onto a piston top. If over revved sometimes the lash pad can jump out if the valve clearance was already too loose. Just pull the valve cover off and look. Quote Link to comment
css1634 Posted April 12, 2015 Author Report Share Posted April 12, 2015 I replace timing chain, guides and waterpump. Still turns over same, jus a little compression on back cylinder. Put air in spark plug hole and air came thru all holes from one. That is what made me think this Quote Link to comment
ggzilla Posted April 12, 2015 Report Share Posted April 12, 2015 Would have to jump several teeth to do that. In which case you need a new timing chain and chain adjusters. Never seen it happen either. It makes quite a racket when the chain gets loose, noisy long before it jumps a tooth. Quote Link to comment
css1634 Posted April 12, 2015 Author Report Share Posted April 12, 2015 Little history, truck was running great, took on 100 mile trip. Next day as i pull into station it died. Never heard a noise, spun over with little compression. Chain did have alot of slack so it wad replaced only to still lack compression Quote Link to comment
css1634 Posted April 12, 2015 Author Report Share Posted April 12, 2015 I would have thought i would hear chain leading up to it, never heard anything, no ticks, taps nothing it was very quite smooth running Quote Link to comment
ggzilla Posted April 12, 2015 Report Share Posted April 12, 2015 So all evidence is that the chain was OK. Slack is normal and taken care of by the automatic tensioner. Quote Link to comment
ggzilla Posted April 12, 2015 Report Share Posted April 12, 2015 The question now is: what is causing the low compression? Common causes include: * incorrectly adjusted valves * incorrectly timed chain * burnt valves * blown head gasket Quote Link to comment
ggzilla Posted April 12, 2015 Report Share Posted April 12, 2015 Oreilly Auto is a great place to get replacement valves. You can hand-lap them in if that's all that's wrong. Quote Link to comment
datzenmike Posted April 12, 2015 Report Share Posted April 12, 2015 I would have thought i would hear chain leading up to it, never heard anything, no ticks, taps nothing it was very quite smooth running Valves may have been too tight! You won't hear a tight valve! Valves cool off by contact with the valve seats when they are closed, specially the exhausts. If there is no valve clearance the valve eventually is making almost no contact and the exhaust squeezes past. It over heats and burns. Quote Link to comment
banzai510(hainz) Posted April 13, 2015 Report Share Posted April 13, 2015 im thinking valve lash fell off or soemthing. No way a chain will jump that far off unless a complete failure on slack side and maybe even that might not totally do it long as there is some tension on tight side. does motor spin around when using the starter? rockauto.com has valves also Quote Link to comment
scooter Posted April 14, 2015 Report Share Posted April 14, 2015 I had one where the chain was changed, and timed incorrectly and it bent most of the valves. Things happen. Check your guides carefully for cracks, and if they feel oblong, you should probibly get the head reconditioned, and get rid of the brass intake seats that let the valves sink endlessly into the head. Quote Link to comment
ggzilla Posted April 14, 2015 Report Share Posted April 14, 2015 Agreed. Use genuine Nissan valve seats, which are compatible with unleaded gas. Quote Link to comment
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