motor issues involving rockers popping out

[GSTwkd]

I was having issues with my car where at times it would start acting like it was missing in the middle of driving for no rhyme or reason. It would come and go from time to time and this went on for about a year or so. Nothing would ever check-out when I did checks for fuel and spark problems. The car became un-driveable without worring if it was going to leave me strandid. So one day I started the car up and it seem to be OK until it got warm and then it started to act like it was missing again so I took it around the block and when I was coming back it died(as if it stalled, no knocking) as i was approaching a stop sign. Did some checks and saw I was getting fuel (42-45psi on fuelgauge on fuelrail), but no spark. Did a compression check and got nothing across all 4 cylinders. Took the valve cover off and found 5 of the 8 rockers on the intake side had come completely off and were sitting at the bottom of the head???? Weird but explains the lack of compression but how the hell did that happen??? Boast related??? So here's comes the million dollar question, if I remember correctly the 4g63 is an interference type motor and is easily messed up from stuff like jumping the timing and so forth and mostly likely my motor is done, right? Looking for some answers as to why this might have happen and looking for some good ideas on new motor set-ups with my current mods. Profile shows lastest mods but for the basics: 20g(21psi), 680's, fmic, s-afc, 3in exhaust. Thanks in advance!!

 

[steve]

Took the valve cover off and found 5 of the 8 rockers on the intake side had come completely off and were sitting at the bottom of the head? If I remember correctly the 4g63 is an interference type motor and is easily messed up from stuff like jumping the timing and so forth and mostly likely my motor is done, right?

It usually takes the valves hitting the pistons to cause the rockers to pop loose. That's directly related to the engine being an interferance design. WHat's likely done is the head. It will need to be rebuild or replaced. The pistons and lower end are usually fine after you clean up any marks from the valves.

Steve

 

[GSTwkd]

"The pistons and lower end are usually fine after you clean up any marks from the valves."

When you say clean up, do you me on the pistons cause I thought if the pistons had any marks I thought they were no good? I was thinking of pulling the head off and taking a look at the pistons tomorrow to see if there is any damage and go from there. I was told by one friend that if they are clean then I should be fine with a head replacement but I just don't want to take the risk of just replacing the head and then later my bottom end goes bad and causes me to get another head also again. Another friend felt that I shouldn't risk it cause he doesn't want me to half-ass it and see me having more problems later. Where is a good place to call for motor and head builds? Let me what you guys think. thanks again.

 

[Irrational]

"The pistons and lower end are usually fine after you clean up any marks from the valves."

When you say clean up, do you me on the pistons cause I thought if the pistons had any marks I thought they were no good? I was thinking of pulling the head off and taking a look at the pistons tomorrow to see if there is any damage and go from there. I was told by one friend that if they are clean then I should be fine with a head replacement but I just don't want to take the risk of just replacing the head and then later my bottom end goes bad and causes me to get another head also again. Another friend felt that I shouldn't risk it cause he doesn't want me to half-ass it and see me having more problems later. Where is a good place to call for motor and head builds? Let me what you guys think. thanks again.

My T belt went and I crushed all my intake valves. When i poped the head off for a rebuild(NAPA ). I just sanded the ruff edges down from the valves hitting the pistons. That was 10,000 miles ago and shes still runin strong.

 

[steve]

Where is a good place to call for motor and head builds?

If you update your location in your profile, people might be able to give you some suggestions.

Steve

 

[BISHILVR]

Just have a local GOOD machine shop replace the bent valves and the cracked valve guides and you will be set, unless you see a hole in the top of a piston, I would'nt recomend trying to sand or remove any metal from the top of the piston anyway since you will definately end up with abrasive in between the piston and cylinder wall, and that will do MUCH more damage than just leaving it alone. No matter how careful you are, you will most likely end up with abrasive where it dont belong. I would like I said just have the head fixed and go, people have been doing it for years and have went tons of miles like that with no problems.

 

[Irrational]

Just have a local GOOD machine shop replace the bent valves and the cracked valve guides and you will be set, unless you see a hole in the top of a piston, I would'nt recomend trying to sand or remove any metal from the top of the piston anyway since you will definately end up with abrasive in between the piston and cylinder wall, and that will do MUCH more damage than just leaving it alone. No matter how careful you are, you will most likely end up with abrasive where it dont belong. I would like I said just have the head fixed and go, people have been doing it for years and have went tons of miles like that with no problems.

an air gun to blow out the "abrasive" left from sanding down sharp edge's caused by the valves hitting the piston's should work fine. I did it on mine and have grate compression to this day. I'm not implying you break out the belt sander, just touch it up if there are any sharp edge's. Sharp edge's like this cause hotspots that can very likely lead to detonation. If you do go this rout after sanding and blowing out each cylinder rotate the engine so the piston goes to BDC then hit it with a clean rag.

 

[GSTwkd]

"If you update your location in your profile, people might be able to give you some suggestions."---Delaware----sorry about that, it use to be up there on the old format of this site back in the day.

Thanks for the input guys I appreciate it. I use to be a regular here and would go to all the meets in PA at the one park but like I said I have been sidetracked for awhile. I'm really hoping thats all I need to do is just the head cause that is something I've been waiting to do for a while now. My plans had been to get a ported head, port-matched 1g intake mani, 1g TB, HKS 264/272 cams, and finish up the rest of the head with some nice internal parts to compliment the rest. The car ran strong before this happen and had been at some dyno days that we had at Xotic. Last time I had dynoed there was a couple years ago when I had my 16g/550s/smic and got about 305whp/342wtq which i was happy about, for the time. But now my goal is to hopefully get closer to 350-375whp on a reliable/street set-up. Again thanks in advance for any and all input.

I'm asking these questions cause knowledge is power and haven't kept up with the current facts and I wanna do it right the first time.

 

[blue1]

Original question was "why did this happen?" you didn't state whether you had done a timing belt or not! To lose rockers if the belt is still in place and timed correctly you will have to look a bit further, has the engine ever been rebuilt before? reground cams? lifters noisy? or just a lack of oil pressure to keep the lifters pumped at constant revs. the nissan S15's did this as soon as you put big cams in them and you didn't fit the Tomie rocker stabiliser plates, but it not common on the 4g's so do a bit of research and keep us posted!

 

[GSTwkd]

The motor was replaced in 2000 by the dealership for what we call crankwalk. It was around then I decided to start moding the car. Only the short block was replaced and they kept the original head(had 50k on it then). I did replace the old lifters with the new ones but that was in 2001. I'm guessing that my crank angle sensor has been going bad for awhile and when I took the car around the block with it acting up/missing, it must have jumped timing when I was hitting the gas. The only thing is it died when I was only rolling to a stop. My rpm's were no higher then 1500 at the time it died.

 

[BrokenTsi]

Just do a head rebuild and you'll be fine. I hit some valves last year, timing belt jumped as soon as i started it, never revved higher than idle. About 10 seconds later, it wouldn't start. Cleaned up the pistons where the valves hit, slapped on a new head, and I was good to go.

 

[GSTwkd]

"Cleaned up the pistons where the valves hit, slapped on a new head, and I was good to go."

From what I'm hearing that seems to be all I need to do. Is that something where I have to pull the whole motor out to do? If so then the labor alone might kill me cause thats where I would need someone else to do that. Thanks again for the replies..

 

[BISHILVR]

The whole motor can stay in, just pull the head off.

 

[BrokenTsi]

Yeah, just yank the head off and inspect the tops of the pistons. If they hit the pistons in the valve reliefs, you can just kinda buff it out. I did it to mine with no issues and drove it a few thousand miles, but since then I rebuilt my motor with eagle rods etc...

 

[GSTwkd]

Thanks for the replies guys! That's what I'll plan to do once it gets a little warmer out here. Pull the head and hope for the best. Then I'll put a nice head set-up with complimenting intake mani, throttle body and a better exhaust mani while I'm in there. Thinking of putting a pair of 272 cams but as for valves and springs I'm still open to ideas. Should I go with 1mm oversized stainless valves and titnm springs? Also still not sure if I wanna go with a ported 1g intake mani(and 1g tb) or a nice aftermarket sheet metal intake, any thoughs? Are adjustable cam gears necessary, cause I have heard that they really aren't?