new guy with a 620

[Cuts metal like mad]

maybe its richened up too much, or you have the dizzy advanced too far... had similar issues when I first got my 620 an started working out the little bugs (too lean and bogging on the secondary). I had richened it up and advanced the ignition timing, which caused it to over rev and backfire on decel really bad... I readjusted the carb (weber 32/36) using the recommended procedure, and backed my ignition timing off a degree or two, and now it runs as good as a carbed motor could. It might still be a LITTLE lean but pulls pretty good when the motors warm and the secondary is opened.

[moparvwfreak]

i'll look into it but i think the carb is shot. timing is at 8* if memory serves. its been a while since i screwed with the timing. i would rather be a bit lean than running fat. hell i pulled 22MPG out of a 318 in a 72 Valiant. most likely killed the heads but meh... whatever. she needs a rebuild anyweay.

[datzenmike]

When warmed up check the choke plate on the carb it should be open like this:

 

http://i138.photobucket.com/albums/q251/datzenmike/carb720shouldlooklikethisLarge.jpg[/img]"]

 

Not like this:

 

http://i138.photobucket.com/albums/q251/datzenmike/carb720notlikethisLarge.jpg[/img]"]

 

If the choke isn't shutting off you will smell the extra gas in your exhaust. Also when the choke is on the fast idle cam will be being being used too. Here you can see the screw with the lock nut, the other end is sitting on one of the 'steps' on the fast idle cam.

 

http://i138.photobucket.com/albums/q251/datzenmike/carbZ24fastidleadjustLg.jpg[/img]"]

 

 

The choke on, will contribute to unburned gas in the exhaust that will light up in the pipes and cause backfiring. The fast idle will also spin the gears faster in the tranny making it more difficult to put into reverse. A constant tapping in the motor is likely too wide a valve lash. A knocking sound that varies (gets louder) with throttle, is likely a rod bearing. Thick oil will only postpone it's life a short while. If it spins it will cut off the oil supply, overheat and actually weld itself to the crank and the rod. On a running motor the rod will likely snap off below the piston and smack a hole in the block side. Drive slowly and keep lots of oil in it. I drove a slant six over thirty miles with a knock so bad I couldn't hear the radio and a 283 a mile and a half home only to hear a loud screeching sound as the bearing went dry.

Edited October 3, 2008 by datzenmike

[fastdadd]

did the issue start after you adjusted the valves

[moparvwfreak]

well right now i have a manual choke on the truck. but i dont think the cam is pulling off like it should. that would explain why it would have to be manually kicked down WHEN i can do it. sometimes it wont. also by the sound of it that would explain the backfireing on decel.

 

as for the knock, its not loud but i can hear it over the exhaust. anything over about 2700 RPM it seems to go away. maybe the exhaust noise is just over powering it. when i got the truck the valves were REALLY out of adjustment. and it tapped like mad. i adjusted the valves and the tapping went away for the most part. i had a few adjusted to tight so i readjusted to spec and now it sounds like its knocking. i dont feel any grit in the oil, even before the change tehre was none. i have had a rod bearing go on me. my first rabbit let a rod go. so i am very familiar with that sound. this is not what i remember hearing in that. its more like the sound a wrist pin would make. light even with RPM knock but it doesn't seem to get louder with the revs. just faster. i hope that made sence.

 

and yes it started not long after i adjusted the valves. so who knows. i have really noticed it the last 3 weeks or so.

[Cuts metal like mad]

maybe a broken ring or rings... some people call that the death rattle...

[moparvwfreak]

maybe a broken ring or rings... some people call that the death rattle...

 

thats exactly what i told my wife. as soon as weather cooperates with me its comp test time. i'll let her warm up then do it.

[Cuts metal like mad]

if the compression ring is intact you could still get good numbers... can you do a leak down test?

[moparvwfreak]

if my compressor is being nice i can. i have the tester on my shelf waiting for its first use.

[lynchfourtwenty]

from what i've seen if you have a rod knock that SOB is gunna chatter an rattle and all kinds of shit on start up.. it'll be like... #%$#^%$&$#%$@#$@# vroommmmmmmmmmmm

[moparvwfreak]

it really doesn't make that much noise on startup. i know it has been blowing oil on startup as i was about 34 of a quart low when i changed the oil. so who knows where its comming from. as said i dont think my little L-16 is long for this world. anyone got an L18 i can get for cheap???

[lynchfourtwenty]

dude phleb is auctioning a l16 off in the sale section to help ratsun.. i dont think the bids are very high yet an its a pretty nice lookin motor.. check it out

[moparvwfreak]

yeah i think i might look at taht.

[]2eDeYe]

maybe a broken ring or rings... some people call that the death rattle...

 

My last 2 motors died that way :(

[datzenmike]

Next time the valve cover is off check the chain guides for wear and the chain for slack. Use a flashlight and look down at the tensioner too. They can rattle on start-up and are sometimes sensitive to oil pressure and thickness. I know a 720 guy who says when his starts to rattle it's time to change the oil and it goes away.

Edited October 4, 2008 by datzenmike

[moparvwfreak]

last time i had the VC off i didn't notice anything. there again that was a while ago. will check that as well.

[moparvwfreak]

well i ran another comp test on it. this time at op temp.

 

#1 165

#2 168

#3 170

#4 165

 

i cant complain about those #s. all within 5 of each other. i also check teh valves. had 3 that were out of adjustment. adjusted those and checked the timing chain guides and whatnot. no issues there either. i also added another spring to the carb. so far i have not had to kick it down to get it to idle. but the pedal is now REALLY firm. maybe thats a good thing.

 

oh and i didn't notice the knock i was getting either. maybe it fixed itsself?????

[]2eDeYe]

Good numbers, at least you narrowed it down...coulda just been valves way out...

[moparvwfreak]

the funny thing is they weren't that far out. omly about.002 in out of spec. but i could hear em chatter alot even though they weren't to bad.

[tdaaj]

it really doesn't make that much noise on startup. i know it has been blowing oil on startup as i was about 34 of a quart low when i changed the oil. so who knows where its comming from. as said i dont think my little L-16 is long for this world. anyone got an L18 i can get for cheap???

 

i've got a running L18, let it go for $175

[moparvwfreak]

might have to look into that. but $$ is not real good right now.

[moparvwfreak]

drove the truck again today and its still rattling. no grit in the oil so i am fairly certain its not a bearing. i am REALLY leaning to a loose wrist pin. if i ahd more $$ i would pick that motor up off ya tdaaj but right now i just cant. i am just going to run it till i have a catastrphic failure and have her towed home. i really need to license my Marquis.... just in case.

 

but on a side note, it no longer does its 3K rpm spikes!!! :D

[Cuts metal like mad]

low oil pressure maybe... hmmm...

[Phlebmaster]

drove the truck again today and its still rattling. no grit in the oil so i am fairly certain its not a bearing. i am REALLY leaning to a loose wrist pin. if i ahd more $$ i would pick that motor up off ya tdaaj but right now i just cant. i am just going to run it till i have a catastrphic failure and have her towed home. i really need to license my Marquis.... just in case.

 

but on a side note, it no longer does its 3K rpm spikes!!! :D

 

Have you considered the L-16 in the "Ratsun Auction"? You could get it cheap, and I would even be willing to help you put it together and get it running.

[datzenmike]

If you suspect a bearing put a new $4 filter on and cut the old one open and do a CSI on it. It's probably fine. Probably just worn bearings which will 'bleed' oil pressure faster than good ones. This will lower the oil pressure at idle where the pressure is lowest.

 

Go to a wrecking yard and find a KA24E RWD motor from a D-21 truck or 240sx or a Z24i from a D-21. This is a hi output (volume not pressure) unit and will bring your hot idle pressure up. Before changing mine on my 300,000km L20B, the hot idle was 17lbs. With no other change but the pump the hot idle went up to 29lbs!!!This was a used pump!! Do not pay more than $20. Tell the guy they are $50 new with warranty. Tell him if it fails he has to buy you a new motor after you sue him... :lol: that'll bring the price down. Don't take any shit from them, just go somewhere else. This is a Nissan part that even used, is better than a re-manufactured one.

 

 

Here is a stock oil pump. You can just barely see the top of the shorter rotors:

http://i138.photobucket.com/albums/q251/datzenmike/motorHi-volumeoilpump1Lg.jpg[/img]"]

 

 

Here is the hi output oil pump. The taller rotors are much easier to see on them. This is the only diffeence.... there is no way to tell from the outside, you have to remove and look down into the inlet at the rotor.

http://i138.photobucket.com/albums/q251/datzenmike/motorHi-volumeoilpump2Lg.jpg[/img]"]

Edited October 7, 2008 by datzenmike