[bandit79jun]

Hi! I have a 403 engine which is .030 bored over. When I got it delivered from the machine shop, I noticed that on the #6 cylinder, at 8 O'clock position, the engine has a dent (or a chip), exactly where the head gasket metal ring meets the engine. The dent is about 1/8" wide or less when seen from the above (the surface that touches the head gasket). But it is on the very border of the cylinder wall. I mean, part of the dent is on the cylinder wall too. It is really thin when seen from the cylinder wall, with the head gasket on. Actually, I noticed it when I fit the gasket on the engine, and there was a little space between the gasket and the engine on that area, whereas on every other cylinder the gasket met all the cylinder surface.

The machine shop guy offered me two possible solutions (at his expense, as he was supposed to see the problem):

1. Install a new cylinder sleeve.

2. Deck the block.

Which alternative should I use?

The engine will have '71 Olds 350 heads, milled .010, with stock valves (which I plan to change to bigger ones), which raise the compression ratio to approx. 9.5 to 1. Stock type pistons. Adjustable roller rockers.

Does it represent an issue with this kind of engine to install a new cylinder sleeve?

Decking the block will raise the compression even more. Is that an issue too with an Olds 403?

I don't want a race car, the car will always be street-driven.

And also, PLEASE NO ENGINE SWAP ADVICE. REPEAT, PLEASE NO ENGINE SWAP ADVICE. Unless this engine meets its unfortunate end, I will not change it.

THANK YOU!

[joe_padavano]

As you are likely aware, the 403 has pretty thin walls to start. Is there even enough meat to get a liner in there? If so, I'd go that route, simply to avoid the potential problems of decking the block (intake fitment, pushrod length, etc).

[bandit79jun]

Well, I asked that same question to the machine shop owner, and he assured me it could be done. The guy does this on a constant basis on diesel engines, so at least he has the knowledge. But since the 403 is a weak engine, I have my worries... I will keep you posted on the results.

THANK YOU FOR YOUR REPLY, JOE!

[FmrStrtracer]

Have you( or the machinist) measured your actual compression(deck height, piston dish, gasket thickness, chamber CC's.

A stock 403, with its factory dished pistons, and factory deck height, shim head gasket, and 4a heads, has less than 8:1 compression. If you replace the head gasket with a standard Felpro(thicker compressed height, {.039}) and only take .010 off the #6 head(usually about 70 CC's stock), you probably wont end up with 9.5:1

I'd measure the deck height and cc the heads, then mill the deck to fix the damage and achieve the desired compression.

[bandit79jun]

Originally Posted by FmrStrtracer

Have you( or the machinist) measured your actual compression(deck height, piston dish, gasket thickness, chamber CC's.

A stock 403, with its factory dished pistons, and factory deck height, shim head gasket, and 4a heads, has less than 8:1 compression. If you replace the head gasket with a standard Felpro(thicker compressed height, {.039}) and only take .010 off the #6 head(usually about 70 CC's stock), you probably wont end up with 9.5:1

I'd measure the deck height and cc the heads, then mill the deck to fix the damage and achieve the desired compression.

Thank you for your reply! Well, while I haven't measured actual compression (hey, the heads have NEVER been assembled to the engine!), I mention the 9.5 to 1 compression because that's what I've always read in several articles over the years that would be the compression ratio for that setup, and not because of first-hand experience. Ok, which compression ratio should I be expecting from that setup?

Another issue: Taking into account the 403 inherent weaknesses (and that I also milled the heads and bored the engine .030 over), wouldn't it be overkill to deck the block too?

[ericnova72]

I'd deck the block to clean this up. I would want to deck it anyway as standard practice just to have a fresh FLAT surface for the head gasket. Compression ratio will be a total guess unless you install one piston+rod assembly and the crank and actually measure the piston to deck clearance so that you have an actual # you can use for calculations. You can juggle it some with a different head gasket thickness.

Sleeving at this point would be a bad move. Yes it will fix the problem bore, but just pressfitting the sleeve will distort the cylinders next to the sleeved hole out of round. To do it right with a sleeve, you would sleeve the bad hole and then bore all to .040" oversize to eliminate this distortion.

[FmrStrtracer]

Originally Posted by bandit79jun

Thank you for your reply! Well, while I haven't measured actual compression (hey, the heads have NEVER been assembled to the engine!), I mention the 9.5 to 1 compression because that's what I've always read in several articles over the years that would be the compression ratio for that setup, and not because of first-hand experience. Ok, which compression ratio should I be expecting from that setup?

Another issue: Taking into account the 403 inherent weaknesses (and that I also milled the heads and bored the engine .030 over), wouldn't it be overkill to deck the block too?

You could end up with as little as 8 1/4:1 depending on the deck height. Your current deck height with the factory machining and factory rotating assembly could be as much as .040. Your machinist should do a mock build on the short block, and measure the 4 corner cylinders for deck height, this will tell you how crooked the deck cut is, and how deep the pistons are in the bores. Measure your head cc's, and then talk with your machinist about what compression you wish to achieve. this will determine how much he'll need to mill off the block. Milling your deck surface is not going to weaken anything, There is plenty of material in the deck.

Originally Posted by bandit79jun

Another issue: Taking into account the 403 inherent weaknesses (and that I also milled the heads and bored the engine .030 over), wouldn't it be overkill to deck the block too?

The 403 is a great performer when built right, and lives well when not revved past 6000rpm. Its a motor designed to make good low end torque and midrange HP. Your choice of heads is a good one, just make sure you get your compression right, and degree you camshaft during installation.