question on engine TDC height

[Eagle 5]

I have a 90 6 bolt sitting in my garage right now. The problem i noticed is that i believe its piston one (closest to cam gears) does not go all the way up. What i mean is at TDC, the other pistons seem to go up to the very top of the block, almost flush basically, piston one does not, its maybe 1mm or so from it. Its notieable that if oyu look at it you will see it. Is this normal or is it possible for some weird reason there are two diff comp ratios in the engine or is it also possible that the rod is slightly bent? I can turn the crank easily and the pistons move up and down without a problem. Doesnt seem like anything is wrong but I dont know. I havent taken the oil pan or front case off yet. Just wondering if any one has any ideas or if that is normal. I can take a picture of it later tonight and post it up.

 

[Eagle 5]

anyone?

 

[ArticNemesis]

The piston should come all the way to the top of the block..

Check your rod bearing clearance first. If that's right, pull the rod/piston out and take it to a machine shop to have them check it for bend/twist. If that checks out, then you've either got a warped crankshaft, or a majorly warped block (highly unlikely.)

 

[Eagle 5]

heres two pics, the first is the piston that is low, the 2nd is of the two middle pistons and how high the other 3 go. casting numbers on top all say 63dt

http://memimage.cardomain.net/member_images/11/web/347000-347999/347224_12_full.jpg

http://memimage.cardomain.net/member_images/11/web/347000-347999/347224_13_full.jpg

 

[Defiant]

Yow. That's not good. What's this motor's history? Something happened there.

 

[MNGSX]

Probably a bent rod...

Sometimes production tolerances can stack in the same direction.... But 1mm is really effd... The think the #1 rod is toast.......

 

[telly699]

 

[Eagle 5]

Not sure on the history. i was told it came from a running car but i know thats crap. after i pulled the timing cover off one of the pulleys dropkicked itself and the balance shaft belt. timing belt was actually fine aside from where they just cut it to remove the head easier. pistons are fine (aside from the number 1) im thinking bent rod but wont know until i open the front case and oil pan here, probably before the weekend.


my question though is, how hard is it to change out one rod? would the piston/rings etc still be usable as long as i replace the rod and bearing?

 

[MNGSX]

You could do that.....

IMHO with the minimal cost at a machine shop to tank. bore and hone... I'd get 4 oe type oversize pistons, rings, 1 1g rod and have the other three checked out.....

The three could have been subjected to the same abuse.. #1 will detonate easier.. Which is why it went first.... Does'nt mean that the other three were at band camp and #1 at boot camp however. .

What are the plans for the engine.... Above is my aboslute minimum I recomend...

 

[psychlow]

That's pretty nuts. Pull those pistons and check for signs of detonation. There might be cracking on the rings lands and other fun damage if they were swift enough to bend a rod.

Can't tell much from the picture, but the #2 piston doesn't look to pretty in that 2nd pic.

Interesting that the rod bent on #1 - I wonder if there is something to that whole theory of #1 and #2 not getting as much fuel as #4 and #3.

 

[ArticNemesis]

Your looking at at least one new rod and possibly a piston.. Maybe even a crank. Make sure the others are checked thoroughly.. Now is a good time for new gaskets / bearings / rings while you are here. Maching the block (a hone at the very least) and some cleaning will go a long way for a motor that will last you.

 

[scottsee]

I see you have TOP LINE pistons. some one has already rebuilt the block. if your serious about rebuilding your shortblock, dississembal everything and take it to a machinest and have them check everything out.

 

[Eagle 5]

i have no idea what pistons they are. i didnt notice the one was lower till i was turning it one day and saw it. also, the other pistons are fine, the crap on them is paper towel stuff or the white stuff from me wiping stuff of when i was scraping the head gasket off. tomorrw im taking the front case and oil pan off, hopefully i can tell from there what may be wrong, if not then out comes everything.

dont really want to do any size rebuild unless im going all out, but guess i may not have a choice. also they are mitsu pistons as the mistu symbol is on them

 

[Eagle 5]

well we took the engine apart. here is a pic of the number one rod.
http://memimage.cardomain.net/member_images/11/web/347000-347999/347224_14_full.jpg
http://memimage.cardomain.net/member_images/11/web/347000-347999/347224_15_full.jpg

I think its bent juuusst a bit. we checked everything else. Pistons look fine, no marks or scoring or sign of any damage to any of them though the middle two looked like valves may have hit them at some point. main and rod bearings/ journals looked fine. no marks or scoring anywhere. also the pistons are mitsu pistons as the mitsu symbol is on them, so not topline pistons. cylinder walls look excellent. beautiful basically, no marks or scoring or anything, rings and all that looks fine. just bent a rod. or whoever had the engine before me bent the rod somehow

 

[MNGSX]

Oh goodie I get an apple and a smiley face sticker.

It's called #1 cylinder runs leaner... He probably ran a bunch of boost w/o enough fuel...

 

[phastalon]

my piston melted when i leaned out. i guess it just depends on how lean it is.

 

[ArticNemesis]

Hehe, bent just a little.??? I retract my statement about taking it to a machine shop to check it being bent... Haha.

Nice rod ya got there... And those are the beefier 6bolt rods eh? Whew, would have hated to see what would happen to a 7bolt rod.

 

[RedRain]

I would check Cylinder #1's Out-of-Round and Taper specs to make sure this engine wasnt run for a while with this bent rod. The cylinder wall could of been wearing out faster than normally with this bent rod.