How high do you rev your Z? My 260 is ill.......

[Ron Earp]

Well I we mangaed to get the car down to Roebling to race this weekend but things went badly. The car had not been running well as I was re-wiring everything, but I attributed it not running well to having sat in the garage for three weeks with a weak battery and little starting.

I got it off the trailer at Roebling Thursday night and drove it around the paddock a bit and didn't like the way it sounded. It was flat, idled rough, and seemed to be getting a little worse.

I took it out for the first session on Friday morning but it wouldn't pull much over 4k and really ran poorly. I bought it in after a couple of laps. Had a look and the engine didn't have the plug I had on the drivers side that seals that tube that goes down into the block. It used to have one, but it blew the plug off. Hmmmmm.

After fiddling some more with it things were definitely worse - there was a plume of smoke coming from my oil can that was definitely under pressure. We borrowed a compression gauge from Gerald Potts (has a nice 325 ITR car BTW!) and found compression was pretty bad across the board:

1- 0 psi
2 - 20 psi
3 - 1XX psi (can't remember but was the strongest)
4 - 120 psi
5 - 90 psi
6 - around 90psi

Damaged rings. Might as well check valves too so we pulled the cover - 12 operating valves and no stuck ones with good oil flow (This check would have made a good Bevis and Butthead episode. All we needed was Mr. Anderson to walk up and say "What the hell?" in the middle of the flying oil scene). Actually, oil pressure is good all around at 40-50 psi when hot and above idle, about 20 psi at idle. Motor has 20 hours on it and was reported to be just rebuilt as new when we bought the car two years ago.

I think I killed the motor at CMP a few weekends back. It was strong at CMP, but I might have been too rough on it. I was running it regularily to 7k and sometimes a bit more in the AutoX section to avoid a shift to fourth. Probably a dumb idea. And, I now can recall the last couple of laps I backed off the motor because it didn't "feel quite right" but couldn't find anything wrong. It still ran well right after that weekend but then the stuff I described at the beginning of this post started happing.

So, now that I've got to pull this thing and re-ring it (as well as bearings, head check, etc.) what do you Z guys recommend as a standard shift point?

Anything you can recommend for the future or for my impending rebuild that can help?'

Ron

[zchris]

If you need pistons you should buy forged as they are now allowed and the cast piston is probably on its performance edge at 7k. 0 compression usually means a holed piston or a missing valve head.
Chris

[Ron Earp]

I agree with you on the holed piston. I might very well have one because I've never seen this amount of blow by before on an engine with cracked rings.

How high do you turn yours?

R

[MMiskoe]

From what you've said here any thoughts that you might have bumped the valves on the pistons? You've got two cylinders that are good, two are fair. One that's dead and another that just moved into a hospice house. I'm just skeptical that the rings care about being over rev'd whereas the valves certainly do. Any ability to do a leak down? It will tell you much more than a compression test as you can hear where its leaking. Its possible you only need head work.

BTW my dad's 280 get upshifted at about 6k (but I've found it at 6500 sometimes when I drive though).

Matt

[Ron Earp]

From what you've said here any thoughts that you might have bumped the valves on the pistons?
[/b]

Maybe, but the valve train does seem intact and operating quite well.

But the amount of gas/fuel/air in the crank case is staggering. More staggering is the amount of metal trapped in the Olberg filter. I popped the top off it last night and the screen is covered with metal

I don't have leak down stuff but I might be able to borrow one.

I thought about some sort of fueling problem that might have caused a leak condition and led to a holes piston or cracked rings. But 1/2 are dead, while 3 is solidly healthy - all fed by the same carb. 4/5/6 are all sick.

[kthomas]

What's the factory redline on a 260Z?

On a 240Z a junkyard stock motor will run 7000 all day long. With forged pistons we went to 7400 when necessary. The weak link is the ring lands on the stock pistons, but the mode of failure is usually just wear leading to higher leakdowns.

To have that much damage sounds a lot like detonation or seriously overlean on one carb. For a long period of time. Rather hard to destroy an L series motor in IT trim. Sorry to hear about that.

[Joe Harlan]

Katman is spot on here. The only other thing I will add is that valve damage can happen on these motors at 7400 but it happens on forced decel. If you were overreving to get through a quick section sometimes the tach gets higher when you are useing the engine for brakes.

[JeffYoung]

One other symptom to add to the diagnosis before we pull this thing apart.

You can turn the crank pulley about 10 degrees in either direction although it appears the cam pulley does not move when you do so. Last, you can also move the crank pully towards the block by about 1 to 2 degrees -- it has that much play in it.

Really crazy that this car ran great one weekend and then went pop this quick. Par for the course with our racing efforts I guess.

[Ron Earp]

One other symptom to add to the diagnosis before we pull this thing apart.

You can turn the crank pulley about 10 degrees in either direction although it appears the cam pulley does not move when you do so. Last, you can also move the crank pully towards the block by about 1 to 2 degrees -- it has that much play in it.

[/b]

I don't know Z motors, but am about to get to know them, but this front crank pulley - is it a dampener too?

If it is a dampener along the design of a Ford SB or similar then this could be explained if the rubber innards that connect the hub to the pulley are degraded in some way.

The crank pulley does indeed turn left or right about 5 degrees. And, as Jeff says you can lift it fore or aft a couple of degrees out of the plane of rotation. The hub bolt is solidly tight. It might have 3 or 4 bolts that hold it to the hub that are loose, I'll find out when the motor comes out.

Joe, I don't think I hit 7400 or so, but there could be some tach error. Definitely hit 7k on occasion. Any tips you fellows can share on Z rebuilds would be appreciated. At this point I think we'll just try and put the motor back the way it was (and I'll take advantage of anything in the rules that the motor didn't have - compression etc.) and get it back out on track. I don't learn about driving working on cars.

Katman, I have some dyno data from one of the motors that was in the car at one time. The data has the dyno shop's name, if I pass that along maybe you could clue me in as to the probably builder in the past in Atlanta?

Just cleaned out my basement for spares to sell on Ebay! Must fund motor rebuild.....

R

[Ron Earp]

To have that much damage sounds a lot like detonation or seriously overlean on one carb. For a long period of time. Rather hard to destroy an L series motor in IT trim. Sorry to hear about that.
[/b]

That is what I think would be the normal cause. And it might be, although the EGTs didn't show anything like that. They definitely showed a difference in temps, the rear three were about 75-100 cooler than the front, but the front EGT that is in #1 never got over 1350 to 1400.

I re-wired the entire car and I made a new panel for it as well re-wired the EGTs. They "seem" to be working, but I've never been all that confident in those gauges. They are some expensive pieces that came with the car and according to the checkout procedure for them they are okay. But I'm still not sure. They'll be getting new probes on the new motor.

Joe or Katman, what do you recommend for forged pistoned?

R

[Joe Harlan]

Ron, couple of notes here, EGT's are a tool. you can have high temps and be to rich and you can have low temps and be too lean. Basicly they are only good if you are inside their window of operation. Read your plugs. Your eyes will not lie to you. 10 degrees of chain movement is excessive. you could tag valves on decel at 7k easy. remember that when you decel you have all the valve spring pressure and drag pulling the cam backwards (whip in the chain. that means if you have 10 degrees of crank slack the cam is retarded and the piston chases the exhaust valve closed. At this point your best bet is just to take the head off and post pictures. That will get you the fastest answers to your questions. The rebuild will not be that hard as long as the bore aren't all beat up from being leaned out. Also i am not sure your hauling situation but let me run one by you. I was the last race of the day several years ago. We came off track and had to travel 4 hours home. Car went straight into the enclosed trailer and the doors were closed. Got home had loads of business so i just left everything in the trailer for about a month. Car went into trailer running the best ot ever has. Month later took the whole thing to the track charged batt and drove it out to change the oil and service it...(at track is bad) Anyway after oil change I went out and noticed the engine was smoking and pushing oil into the breather. When I took it apart there was damage to the rings and a couple of broken ring lands. After a complete autopsy we discovered that moisture was the cause of the failure. There was signs of rust in the bores but the gaskets were fine. the real signs were surface rust on the interenals of the engine components. The race oils we use do not have the same moisture inhibitors as street oil and combined with being locked in an oven for a month I am sure that I was the cause of the engine failure. Good luck. Pictures always help

Edit: As far as pistons go I am still a hold out for OE stuff. These days if you want to run a forged piston any of the big manufactures are good. the down side is most of that is custom and this time of year you need 6 to 10 weeks to get them built.

[JeffYoung]

The plugs did not show an overly lean condition at all -- I just don't think that is what happened although I agree it would appear to be the most likely cause.

Joe, you know my technical knowledge is lacking -- can you help me with a question? Why would the crank pulley turn 5 degrees or so, and the cam pulley NOT turn the same amount? Is it possible something happened to the crank and the pistons and valves did some smacking?

We'll get pictures up as soon as it is apart.

Thanks guys.

[Ron Earp]

Joe, you know my technical knowledge is lacking -- can you help me with a question? Why would the crank pulley turn 5 degrees or so, and the cam pulley NOT turn the same amount? Is it possible something happened to the crank and the pistons and valves did some smacking?

We'll get pictures up as soon as it is apart.

Thanks guys.
[/b]

Hey Jeff the crank pulley is simply bolted on the end of the crank and has nothing to do with the cam gear, cam, or valve timing. The cam gear it secured on the crank and does not have play in it, and neither does the cam. Chain is properly tensioned too. I have not checked cam timing, but the pulley is independent of all that.

To be clear the crank pulley is what has about 5 degrees of play in it, and in the current state it allows one to turn the water pump and alternator a slight amount. I think the crank pulley has an inner and outer section (I've not checked yet) and the inner section has somehow become slightly detached from the outer section which allows some play in the plane of rotation, and, allows you to pull it fore and aft a couple of degress too.

Joe in between the CMP race and this race three weeks elapsed. But the car came straight off the trailer Sunday night from CMP and into my garage, which is at a nice 70F. I worked on it for three weeks, intermittently starting it from time to time to verify my wiring work. During this time it ran poorly, but I thought it was due to the frequent starting and shutdown and lack of revving. Where I live I can't fire up race motors much and definitely can't rev them over 1.5-2k or so, just when moving the car around. So, I figured all the rich starting and idling was causing the motor to sound poor and run badly.

I'll get lots of pictures up, I like pictures. Probably later in the week we'll have some photos of motor out and parts.

R

[Joe Harlan]

Actually Ron you were probably correct about the poor running and rich fuel being what started the issue. You could have fouled the plugs enough that forcing the engine to run on very dirty plugs and raw fuel in the system could have led to the possible detonation you may have experienced. Now as far as the crank pully goes. Yes it is 2 part and yes they fail. You need to turn the crank by the bolt one direction and then the other direction to confirm chain slack. These engines will have slack from no oil pressure to the tensioner unless it has been properly installed. Jeff, Excess Slack in the chain will allow the valves to make contact under decel and I have seen it a bunch of times in IT engines when you add soft valve springs to it(valve float)you can make contact on up shifts. The 2.4 engines it is not uncommon to see little smiles on the piston tops from the exhaust valves.

[Ron Earp]

Now as far as the crank pully goes. Yes it is 2 part and yes they fail.
[/b]

That explains the crank pulley then. Fords are two part too, in some applications, and do the same thing.

We'll have to check everything else when the motor gets opened up. It'll be interesting to see what we find - holed pistons, cracked rings, broken valves, bent valves, or all of the above! Maybe we need a lottery and a $10 prize!

R

[Joe Harlan]

Ah, Now I will also save you some future money...Before you take the engine apart take the head off rotate to TDC and check your timing mark alignment. It is not uncommon for the outer ring to rotate before these balancers fail. If all is good then scribe a mark across the two part so you can have a qucik look with a mirror before every race..

[kthomas]

"Katman, I have some dyno data from one of the motors that was in the car at one time. The data has the dyno shop's name, if I pass that along maybe you could clue me in as to the probably builder in the past in Atlanta?"

PM me and I'll see if it rings a bell, but if it was a chassis dyno it most likely won't help. I'll be at TGPR tomorrow flogging the BMW but I'll be back in touch tuesday.

We used JE for the forged pistons. Stockers were up to $73 each last time I looked, which was quite a few years ago, and the factory quit shipping groups of 6 from the same casting lot, so we bought a bunch of pistons to find 6 we like last time we used OEM.

Most EGT gages are too hard for a driver to read, they're really dsigned for aircraft applications. We eventually replaced our dual EGT gage with blinking lights o2 sensor. You know, something the PITA carbon lump in the driver seat could understand.

[Ron Earp]

I'll get that data out, it is from a flywheel dyno and you might know the shop.

Dang, pistons are not cheap, and forged will be a long time to get it looks like. Maybe, just maybe, we'll get lucky and have some pistons that can be re-used. But I doubt it. I think we'll be in for an overbore with damaged pistons.

Jeff and I will sort something out and look this week while checking cam timing, tension, and timing. Thanks for all the help and replies on this one.

R

[[email protected]]

Everyone else has covered this well, the one thing I can add is that the valve springs won't last forever. Change then every 3-4 races depending on how high you rev. If you are regularly going over 7000, like running a 4.11 at Rd Atl, change them every weekend. This will save you a lot of trouble down the road.

As you get ready to build back, if you are building yourself, I have a torque plate for the Z engine. I am in Shelby NC. I was amazed the first time I measured a block that had been done with a torque plate. The difference is huge.

Mike

[Ron Earp]

Jeff and Jeffery came over and got the engine out for me last night. We tore it down til the head came off and stopped. Timing was good, chain good, etc.

But, two of the pistons have have chunks out of them and I think a third is about the go as well. That will definitely explain the compression issues. In looking through the truck load of spares that came with this car I also notice that there is a set of "dead" pistons attached to rods. One of those pistons shows exactly the same little half moon burn through that looks like these. I've enclosed a picture of the piston that it out of the spares, but it looks like mine from the top (mine are not out of the block yet).

I've not inspected the head yet. All the pistons have little smilely faces on them, just as you said they would. Looks like it was built using ARP stuff throughout and with OEM pistons. I'll get more pictures up once I work out this time limit and global attachement size thing on this board.

Ron