Timing damage? I hope not...

[trogdor1138]

I recently rebuilt the engine in my 1971 240Z. The relevant parts:

L28 N42 block

L24 E88 head (earliest "notched' chamber design)

Overbore of 0.030"

F54-type flat-top pistons from ITM

Isky Racing Stage 2 cam (.480 lift, 280 duration, 232 @ .050 lift duration)

New Schneider performance valve springs and hats

New rocker arms and lash pads

New oil pump for 81 ZX turbo engine

As part of the machining the head got a valve job (head already had steel valve seats retro-fitted) and new valve guides. I'm running 91 octane gas (highest we have here in Utah; high altitude) and Valvoline VR1 racing oil. The new camshaft is internally oiled and I installed a new spray bar made for me by Captain Obvious on these forums.

Everything in the block was assembled with Permatex's assembly lube while everything in the head got Isky's assembly lube included with the cam. All the bolts and nuts I could find a spec for got torqued to spec.

When I first fired her up the radiator was open and had a hose constantly running water. I immediately brought the engine up to ~2000 RPM and let it run for 30 minutes while I monitored oil pressure and temperature. Temp was right in the middle of the gauge while oil pressure was about 80 PSI. She sounded great.

A day or two later I took her out for the first drive. Engine revved nicely and was very responsive. I stayed in first gear initially, bringing the engine up to ~3000 RPM and then letting the engine brake the car to help seat the rings. I did this about 10 times, then took her out on the road.

Just a minute or two after shifting into second a clunk sounded under the hood. I immediately pulled off the road, popped the hood. The gauges still read in the normal range, but the sound was markedly different and idle was terrible. I head back home when another clunk sounded. I immediately killed the engine and coasted to the side of the road. I tried cranking a few times, but the sound was wrong and the car wouldn't start. Through all of this, no smoke, no leaking fluids, and no extreme gauge readings.

The next day I had the car towed home. I pulled all of the spark plugs; none of them show anything unusual and definitely no signs of collision. I pulled the valve cover; camshaft looks good and well-oiled and all friction surfaces appear to be mating nicely. However, the cam timing sprocket had slipped off the cam snout and was no longer engaged with the dowel on the snout. The sprocket hadn't fallen into the abyss of the front cover, but it was riding on the bolt. I didn't see oil at the top of the radiator, and no frothiness in the oil on the dipstick.

I figure that the clunks I head were the cam timing sprocket slipping off. I must not have done the final torque to spec on the bolt as I thought I had. I can't turn the cam enough to engage hole 1 on the cam timing sprocket so it appears that the valves and pistons did run at least some interference. However, nothing on the top side of the head shows any signs of trauma.

I'm pulling the head tonight and will be pulling the front cover and re-doing the timing this weekend. What specifically should I be checking? I figure the most likely damage is bent valves; what do I need to do to check for this? Any other advice?

[d240zx2]

You summed it up nicely. You probably have a bent valve or two.... :-(

[siteunseen]

Oh wow, that stinks. I'm doing the same thing as you right now. That nut will be in my mind for sure.

[zKars]

Pretty hard not to have some valve damage with what you mentioned having happened. Definitely sucks. The devil is in the details ain't it? Lock tight and proper torque specs... Good thing we like workin' on 'em as much as driving 'em, right??

[trogdor1138]

So, I pulled the head tonight after dinner. The sum total of the damage appears to be:

- 3 piston heads where valves made contact

- 4 valves that are bent

- A few valve seats that have cracked

Also, one of the lash pads popped off its valve stem and was just sitting in the oil channel. Two of the pistons only have very light nicks; I feel fine keeping them in service. The third, however, has pretty bad gouging. I think its bad enough to warrant replacement. I'd like to simply resurface the head of the piston, but I hate the thought of shavings getting into the oil or embedded between a ring and the cylinder wall.

It's a pain that I'm going to have to break down the block again, but overall things could have been much worse. Actually, don't some people claim to have done ring jobs with the block still in the car? I only need to pull cylinder 1, so if I could avoid pulling the whole block that would be nice. It seems like I might be able to remove the oil pan in the car... any thoughts?

[Zed Head]

Not my idea, but packing grease around the perimeter of the piston will allow you to do some grinding without getting the chips where you don't want them. Pack the grease in, do your work, scoop the grease out with the chips embedded. I think that I read about it from people doing valve reliefs in their pistons.

[olzed]

Pictures of the piston would be good.

[siteunseen]

I've read shaving cream in the cylinders to keep chips out and also read a post about somebody that was able to unhook motor mounts and jack the engine up enough to remove oil pan then push the piston through the top. I wish I could remember specific names or post titles to keep you from having to do alot of searching. I always just google search and get better results. The search on here doesn't filter out junk as well as google does. Good luck.

[siteunseen]

It's out there, just googled and got this real quick

Just want to note that I surveyed the archives and found all the hints for removal of oil pan while the engine is in the car BEFORE I attempted to do this on my '76 280Z to replace a leaky gasket. And I must report, once you know the tricks, it is a very simple process requiring no removal of crossmember or jacking of engine. Since the hints were scattered in several posts, I thought I would take you through the process with all hints in one place:

1. Jack car up on crossmember and block it there. Even better, I slid ramps under the front wheels (the car is too low to drive up them). This gave me plenty of working room, and was much safer than jack stands.

2. Drain oil. Remove dipstick.

3. Remove all pan bolts. Note that there are two different-length bolts used on the pan. The longer ones go throught the angled metal "spacers" or whatever they are on rear sides of pan.

4. Remove bottom two bolts in the tranny bellhousing. The pan will hang up on them otherwise.

5. On my car (76 280Z), there was a small "anti-torque" thing on the steering rack. It's put together with a U-clamp like you'd find on an exhaust clamp, and is there I guess to keep the rack from twisting. Anyway, mine was situated at the driver's side of the rack. It's in the way for lowering pan. It's simple to loosen it and either remove it or (as I did) simply slide it to the other end out of the way.

6. Knock pan loose with rubber mallet. After 20+ years, mine was almost 'welded' on and had to be pried loose with screwdriver, which actually bent one corner before it would bust loose. You may have to go this way, too, but try to do it only as last resort. Straightening small bends in pan rim is no big deal.

7. Loosen the two 12mm bolts on the oil pickup. They're on the driver's side about halfway down the block. Be careful not to damage the thin gasket. You don't have to actually remove this piece, but I did so to clean it up and replace the gasket.

8. Once the pan is loose, you can get a flashlight and see where your rod journals are situated. The pan will not come out unless the front journals (or more accurately, the crank counterweights in front) are rotated up into the engine. So you need to get your 27mm socket on the crank snout and turn with a big ratchet or breaker bar. (I meant to see where this was compared to TDC, but forgot.)

9. Once the frontmost counterweights are up inside engine, the pan will slide back, down and out. It's a tight fit and takes a bit of jiggling, but it will make it.

10. To install, "reverse the procedure". If you've removed the oil pickup, screw it very loosely into position BEFORE you slide the pan on. Once the pan is back in position, don't forget to tighten the oil pickup bolts before you start in on the pan bolts.

I tried sticking the pan gasket on with sticky sealer, but you have to wiggle everything around so much, that it still came loose. It's okay. You can fudge it around when the pan is in position, just be patient and make sure all the screws are indeed going through the gasket. Finally, do NOT overtighten pan bolts. I think they spec out at 7ftlbs. The pan gasket I used was so thick and squishy that I had to make 3-4 passes around with a small torque wrench before they would 'hold' torque. Also note that there are two or three bolts on the passengers side under the crossmember that you'll have to do with a box end, as you can't get a socket on them.

11. Don't forget to put oil back in the engine! ;-)

Edited May 8, 2012 by siteunseen

[Diseazd]

I would have a machine shop check your piston rod. Wouldn't want a bent rod on the number 1 cylinder. Just a precaution.

[trogdor1138]

Thanks everyone for all the feedback and sympathy.

The piston face damage ranged from a slight kiss to some minor gouging. I dropped off the head with my machinist this morning, and he feels pretty good about the shape of the pistons. Sorry for the bad quality, but it's really tough to photograph something very shiny in a dim garage.

As you can see, the pistons aren't in too bad of shape. My plan right now is to bring each to its top center, then tape over the gap between piston and cylinder, coat with grease, and lightly smooth out the nicks. Irritating that I have to do this, but it could have been much worse. Besides, I now have custom eyebrowed pistons

[Gary in NJ]

It's heart breaking to see those marks on such new pistons.

You're not the first to have to rebuild a fresh engine (I know a few) and you wont be the last. It's a club no one want to belong to.