Does metal float?

[speedo]

Sure does when you miss a shift...valves float. Pulled the heads and cam towers last night on a 2.4 and knew before starting the teardown that the compression numbers on 123 and 4 were 90-95% but 5 was dead and 6 was 60%. I figured bent valves. Now with the heads off and pistons exposed, it's plain to see....littlle divots in the pistons from both intake and exhaust valves, and the 5 and 6 exhaust valves are indeed bent. I'm going to presume that as long as the pistons aren't broken, that my best bet is to leave them alone and focus on the top side. I figured that trying to polish out the divots might create an imbalance between the pistons and that the volume in the cylinders hasn't been affected. My machine shop will disassemle the tower and heads and check all the valves and guides and machine and replace where necessary. This is only a 2.4 and my interest is not in owning a $6k rebuild. Anything else I need to watch for here?...I'm psyched to clean up the outside of the motor as it goes back together...maybe detail a few things. ..using the suggestions from Waynes book.

[Tim Walsh]

ouch that really sucks even if it is just a 2.4. Take lots of pics and post them

[speedo]

Heres what the pistons look like. The dings on the exhaust side are minor and have not changed the surface area dimensions. I checked the heads on my bench by rotating the cams using my cam-holder tool. Good side (123) had ok valve clearance and appeared to have no problems. Bad side (456) confirmed prblem vaves on 5 and 6. I'm going to have the bad side machined and replace what is necessary...guides valves etc. Should I worry about the heads or just bolt it back up. Fortunately all the studs are solid. I'm trying to rationalize what else could have happed to the motor during this event as the PO was there and I wasn't. Whadayathink?

[zotman72]

Lars:
Looks like a T motor to me, where are the alloy cylinders and S pistons you mentioned?.....
Anyway, I would replace all guides as a matter of principle unless it is readily apparent they have been replaced recently. Get new rings and take just one rod off to determine the state of the bearings. If the bearing is good, reassembled. Oh you might make the BA mod on the tin around the cylinders if it has not been done already. Oil o-rings on the rocker shafts too. Might check the rockers, especially those that were on the floated valves, get them resurfaced and perhaps rebush if necessary.

Good luck!
Bill

[speedo]

Heads are at the machine shop now...he's going in with an open mind. Should hear soon how the valves / guides / rockers fared. I told him that if the guides were ok to leave them, and to go ahead with a valve/head job and polish the rockers if necessary. Depending on what he finds, I may go ahead and replace the rings and check the rod bolt bearings.He was suggesting that a good use of $ would be a more aggressive cam...he'll check to see what cams are in there now...does this necessarily mean find a set of s cams? He mentioned something about that being standard procedure when the webers were installed.

[zotman72]

You have a T motor, with T components. What will S cams do for you? Nothing as far I know (which is not much) without making other critical S mods, such as porting the heads, bumping the compression (currently 7.5:1). Going with JE pistons or S ones if you can find some. Make sure you check your ring land gap on the top rings. You might have exceeded your wear limit. Oh is your wrench in town (Denver metro?), has he done this S cam mod on T motors before, what sort of hp increase is claiming will result? I personally would not do it unless there is promised (dyno verfied) results offered.
HTH

[speedo]

I'm having Ron over at the Buick dealership on east Colfax do the head work...says I should use some of those late eighties Skylark "high-lift" cams! Actually Eisenbuds is doing the work...if thats not a good idea, thanks alot for warning me.I just went over to Dart yesterday and picked up some need-some-work black leather seats out of that black carrera, some h4s, and swapped out my chrome for black trim !!! Still searching for some 993 mirrors. My fiberglass should arrive tomorrow. Heres a rear end shot with his new wheels...225-50-16s...looks like Dart salvaged the wheels off a car in a pasture!

[snowman]

Clean those piston tops really well. Check with a small magnifying glass to make certain that there are no cracks or holes in the piston. They can be really hard to see in all that dirt.

Are you certain that the valves floated and it wasn't the piston traveling to far out due to bad rod bearings? Less likely but possible is a cracked crankshaft These are possibilities, maybe not highly likely, but not unseen either. You should be able to check without breaking the case.

You can put E cams in a T engine and get a big boost in power, probably enough to break it if you hot rod it to much without the improvements in cooling. Other parts may or may not take it are: the crank, rods, pistons. I understand a lot of people have done this mod (the E cam)and like it.
The T cams can be reground as E's.

[speedo]

Jack, would the motor have run with a broken crankshaft? God, I love these old motors!!I'll ask the shop to check into the "E"-grind....if I go that route I've got the set-up for the front oil cooler in my new glass bumper....just need to find that early RX-7....hmmm where did I see that old mazda just sitting. ....?

[snowman]

Yeh they do still run with broken cranks. Not well though.

[Wayne 962]

I wouldn't clean the pistons if you are not planning on removing them. You'll get carbon everywhere, like in-between the piston and the cylinder...

-Wayne

[Britwrench]

Agree with Snowman here, had customer miss shift at the track with 2.4T, same damage. Checked the pistons and found at least two cracked at the top. Be very careful inspecting them.

[snowman]

Removing the cylinders and pistons is no big deal. Just mark them first.

Start by marking everything.

Remove all the cylinders, very simple, just pull them off.

Remove the pistons. Remove the clips and use the back of a 3/8 extension to drive out the pins.

Clean the pistons by soaking them in tide and hot water for a couple of hours.

Tape up the rings and ring lands using masking tape.

Have the pistons bead blasted. UGG I hate to say this because the beads can stick to the piston and do much damage if not removed. NEVER bead blast the ring lands. Use scrapers or an old ring for this. I know this is done all the time but according to engine rebuilding news letters, it is a common reason for failures. Thats the real pros, not amateurs talking there. Their livelyhood depends on doing it right, so you gotta beleive them.

If you inspect the pistons very carefully and see a crack, you know you have to replace them. If you do not see a crack and really really want to be sure you can buy dye penetrents for about $30. It is a red dye in a spray can. Just spray it on, wipe with some spray on cleaner, let it set for an hour, and spray on a developer. Any cracks will show up big time.

No cracks, clean again in hot water and Tide laundry detergent. Brush the surfaces to make sure all glass beads are removed.

Make sure to use new piston pin clips on reassembly. They are avilable. See any shop that does a lot of rebuilds for these.

WAYNE- it would be a real service if you could sell these things. They can be hard to find for the weekend mechanic. A couple of bucks for the lot, but they could ruin your engine if you do not replace them.

[speedo]

You guys are great! I went out into the shop last night , pissed-off because the sandblaster didn't show up for the second time and I figured some wrenching would mellow me out...I brought a magnifying glass to check out the pistons...no cracks that I could discern. I started to pull the cylinders to get at the rods-bearings etc and I stepped back. The deeper I go into this motor, the further I am from what I was intending this project to become...an RS. What needs to happen to this motor is going to come from the hands of someone who wants to end up with a rebuilt 2.4-2.7. I'm going to drop a 3 ltr in the car. I'm going to post the motor on the classifieds. A lot of the dissassembly is done and the buyer can see exactly whats here...so if you know an "early guy" in the Denver area who needs a 2.4 with 40 IDA webers....

[snowman]

If you really want an RS you are doing the right thing.