KJL

I am in the process of installing a new cam and heads. I know bottom end has been rebuilt at some point in time. This is my first trip inside the engine so I thought it would be a good idea to do a check of the bottom end to make sure it was in decent condition.

The pistons appear to be the stock dish with 2 sets of valve reliefs.
Block does not appear to have been decked. (numbers visible)
Cylinders have been bored .020 over
Cross hatch still slightly visible
Other than some carbon crust, could not detect a "ridge" at the top of the cylinders.
The single non-roller cam timing gear was badly worn.
Rear main cap has an oil clearance of approx. .0025
Pulled a rod cap and it checked to .0015.
My cold cranking compression was approx 155-160 psi for all cylinders.

Based on the above, it would seem the bottom end is ok. My questions:
Should I attempt to clean the carbon from the cylinder heads?
Is the fact they used the stock pistons in a .02 over bore ok?
Is it possible to hone block and install new pistons with block in car?(I would like to go with flat top pistons.) Honing without a torque plate may not be a good idea.
Thanks for the replies.

Keith

Paul 75 L82

I would clean the carbon off the top of the pistons and move on. A new oil pump for sure since you have the pan off anyway. Sounds like your off to a good start to your project.

Alwyn678

What cam and heads did you decide on Keith??

Twin_Turbo

if you are honing just to break the glaze you don't need torque plates. However, if you are only glaze breaking I suggest you get a bubble gum hone, they are much easier to work with and the results are excellent.
This will also take care of the carbon buildup on the top of the bore.

Those pistons are not stock, they are probably stock type .020 over (are they cast?) The stock type pistons can be bought in oversizes. They could also be Sealed Power (federal mogul) hypereutectics.

Check the bores for taper, if you set the ring gap do it in the bottom part of the cylinder since that is least worn. If you set it at the top the taper which may be there will make that the gap is too narrow for the bottom.

You can install new pistons, just make sure you set all the tolerances at the narrowest point (bottom of bore)

As for the heads, sure you can clean the carbon off. Check the valve guides for wear, check the seaets. Also chech the valves (glass bead blasting the backside will reveal cracks)

Marck



[Modified by Twin_Turbo, 12:46 PM 2/11/2003]

KJL

Marck,
I think they are cast, they are a very light almost white /grey color and have numbers which are cast on the underside. I am not sure how to tell. How do you know they are not stock? Why would dished pistons require valve reliefs?

KJL

Al,
After much research and speaking with Jerry, I have decided to go with the XE256H instead of the XE250H. I am also going to go with the Edelbrock RPM 64cc heads with 1.6 ratio rockers. I put out a post regarding the 327 350HP GM cam yesterday and the replies swayed me towards the XE cam.
I pulled the cam and heads this weekend. Placing the BIG order with Summit today. Man, my cam timing gear was lose and very worn. The profile of the chain was worn into the gear!!

Twin_Turbo

simply because your engine is .020 over the pistons are for .020 over too. They CAN be stock type cast, badger made those and some others too I think. There are similar pistons in hypereutectic and forged form.

Why would dished pistons require valve reliefs?? huh, I don't think I quite follow you here. The stock cast pistons have 4 valve reliefs because that way they are very easy to install, you can't have them the wrong way around.

The small dish in the stock valve still requires reliefs since the dish is not deep enough for the required valve clearance

The L82 pistons have 1 big valve relief and they can be installed on either side of the engine too, just w/ the reliefs on the correct side. The pistons w/ a non uniform valve relief (like the KB hypereutectics) that have a small and big cut for the exh & intake valve can only be used on specific cylinders (because the position of the valves alternates)

Marck

Twin_Turbo

as for the chain being worn into the sprocket, if it's the stock nylon covered teeth one, it's not weird they are worn into the sprocket.

Marck

KJL

I checked the bore diameter at the top, just beyond the crust ridge, could it have worn .02 over? Again there is not much of a ridge. I checked with a digital caliper.

As for the cam sprocket, it is steel..... :eek:

Thanks!!

Twin_Turbo

Hmmm that sounds nasty :)

Yours sounds rebuild, the cast stock type pistons are generally available in oversizes so that's not a good way to determine rebuild or not

Marck

Alwyn678

Congrats.......That sounds like a sweet set-up.....I can't wait to see how it runs.......Let me know if i can help you with anything..I will be more than happy to help ya and get dirty

Twin_Turbo

No, it's not worn, it's overbored and it has stock type pistons installed. Very common.

Get a bore dial and check for taper (or install a ring and measure the gap difference in the top & bottom of the bore, you can calculate the taper from that)

If the bores are not scratched and the taper is not too bad (probably not since you don't have a ridge) you'll be fine after some glaze breaking. If there is excessive ridge you'd have noticed it when you removed the pistons because the rings would have caught behind the ridge.

Marck