Got engine apart

[BarryC]

I pulled engine out and pulled it apart to re-gasket it to stop aggravating oil leak. Pulled the heads off to look at pistons. I forget over the years what was in it. They are kb 1279. They are a dished piston similar to the originals, but they seem to sit way down in the cylinder when at tdc. The block is still standard bore with less than 25000 miles since rebuilt 15 years ago. Calculating my compression ratio shows that I only have about 7.5:1 with the heads, gaskets, and pistons I have. Does this sound right? I'm guessing that is why I'm down on torque and power. Not saying that it runs terrible, but it doesn't run like it did before the major rebuild when it was original and untouched. Could I change pistons without doing another complete overhaul? Could I just change the pistons out to a higher compression pistons and put it back together with new gaskets? Would u use the same rings or new rings? Remember this doesn't have hardly any miles on it. The cylinders still show the good cross-hatch hone pattern with no ridge at top at all. I do remember putting moly rings in it back then. I'm hoping to get more performance than the factory gave me. Please help.

Thanks,
BarryC.

 

[AdamR]

KB1279s look like they are a stock replacement. The KB107s would be a better choice for performance. Those would probably bring you up to around 9.5:1 with out decking the block. However with 25,000 miles on the rebuild build its unlikely you could get away with swaping pistons with out boring the block.

 

[BarryC]

Are my calculations pretty close on the compression ratio? Factory it was rated at 8.4:1. Am I anywhere close to that now? What about the pistons being down in the cylinder??

 

[BarryC]

Also, how about some help with my oil leak. Seems to be coming from rear oil pan seal. Tried twice in car, but no luck. Thats why I pulled engine. Looks like seal is getting split lengthwise and wants to bulge out. I'm using Fel-Pro gaskets and seals, but seal seems to be a little long. Doesn't seem to fit down in main cap groove really good. Pan looks fine. Any ideas??
Thanks, BarryC.

 

[340sFastback]

I just put the oil pan back on my engine yesterday using FelPro oil pan gaskets. With it on the stand wipe the block's gasket surfaces down with Brake Parts Cleaner and clean paper towels. Keep wiping until its completely oil free. Then place a thin film (again thin, very thin) of gasket sealer where the side pieces go, put more in the 4 corners, enough to squeeze out slightly, like a small bead in those area. Then press the side pieces onto the block. Wipe excess from the top of the gaskets in the 4 corners. Keep pressing the gasket into place for the next 15 minutes or so. Then let it sit for two hours.

By the way I cut the little rubber ears that stick out of the main cap on the rear with a sharp razor. Those little ears cause a lot of problems getting the side pieces to sit flat so carefully cut them off with a nice sharp razor flush with the rear main cap.

On the oil pan make sure the oil pan gasket surfaces are scraped clean. Then wipe down with Brake Parts Cleaner and paper towels just like you did the block. Put thin film of gasket sealer where the ends fit into the pan. Put end gaskets on pan. Yes they will stick down out of the pan slightly, that is normal. I then put a very very thin film of sealer on the side pieces that are now set up on the block (very thin film). Put a bead in each of the 4 corners on top of the side pieces. Not a big bead, just a little one. Now carefully place pan onto engine and get one bolt starter on each side in the middle. Just started, not tight. Check end seals to make sure they are still straight. Then install all bolts. Now carefully cross tighten bolts. I like to take the end 4 bolts down first, alternating between those 4, because the pressure is squeezing the ends down.

Take you time and be careful. Then enjoy a leak free engine for a long long time.

 

[340sFastback]

And when the engine was put together you did put a thin film of RTV between the rear main cap and the block correct? Otherwise oil will leak out between the main cap and block.

 

[lead69]

Are my calculations pretty close on the compression ratio? Factory it was rated at 8.4:1. Am I anywhere close to that now? What about the pistons being down in the cylinder??

Did you measure how far down the pistons are at tdc?,I would get a definite compression ratio by cc ing the heads ect.Even if everything checks out you really need to balance the assembly with new pistons,I would see where your at and maybe do a light mill on the heads and change to a thinner head gasket if this isnt done already.

 

[moper]

If it's still std bore, then adding new pistons will still leave them lose in the bores. If your choice is KB hypers, then this simply wont work well. I will also say technology has come far in 15 years. I would do a rebuild on the lower end, meaning check the crank and rods, chances are they are fine. But plan to bore and hone the block, and plan to re-balance the assembly.