ajr2820

I am building my 455 and need some help. I bought it right after the PO had it rebuilt as a 0.030 over low compression engine. I am bumping up the compression with Wiseco +15.0cc forged aluminum pistons. Wiseco suggests a 0.0035 clearance for the piston. My issue is that I am measuring the bore at 4.154. This would only give me 0.0025" clearance. Would you install them without further machine work? Would a ball hone clear this up? It is possible that some of this 0.001" tightness is human error in measurement.I had a tough time zeroing the bore gage off the micrometer. This will be a street engine, not a race engine.

cutlassefi

green1972

When I bought my wiseco's the machine shop boring the block called them and for a Olds they said to give .0040 clearance, 10 years now and no problems, too loose you get noise at startup, too tight it will run hot, Tim

OLDSter Ralph

Have BOTH the pistons and the bore checked.

ajr2820

The pistons have been measured. I have done that myself with a micrometer. My issue was getting the dial bore gage zeroed and measuring the bore. I was finding it very tough to get the zero set to 4.155" on the bore gage. The best measurement I got was 4.154", but as hard as it was to get the gage set I'm wondering if the 0.001" of tightness I am measuring is just an error on my part.

OLDSter Ralph

Sounds to me like you need a second pair of hands and eyes to check piston sizes and bores. A second pair of hands and eyes are always good to confirm measurements. It may seem like a waste of time now, but if you have to do it over later, you'll wish you had done it right the first time, I would want the same pair of hands measuring BOTH the pistons and bores.
...........Just my two cents worth

BillK

Make sure you are measuring the pistons at the correct place. The pistons should have come with a sheet showing the correct gauge point. Measure the pistons and then lock your micrometer. Put it in a micrometer stand or even clamp it in the vise with a couple of rags to protect it. Then zero your bore gauge to the micrometer. That way the bore gauge will show the actual clearance.

Also, what temperature are all of the parts at ? If the block and the pistons are not both at about 68 degrees you will not get a correct measurement. You would be amazed at how much they will change. Same with the micrometer. You can change it by just holding it in your hands too long. Thats why I pretty much keep my shop at 68 degrees 24/7/365

If you dont feel comfortable with it have your machine shop check it for you. A little extra clearance is always better than not enough.

A ball hone will NOT take a thousandth out. Needs to be done with a real honing machine.

oddball

Home stuff is good for double checking things, but the parts should go to a shop if there's any questions.
I use a bore gauge and mics to verify my parts, but I recognize the limitations of my skill and my cheap tools. Any shop will have much better tools and fixtures and be able to get more accurate results.
Most shops will do a quick check without busting your *****. It's worth taking the time now rather than breaking parts later. Especially with forged pistons - looser is much better than tighter.

ajr2820

Block is in the back of my truck today to drop off at the machine shop. The largest piston measured 4.1523" and the smallest measured 4.1519". The bore measured 4.1540". Getting it honed out to meet the 0.0035 minimum clearance. According to all the measurements, I need another 0.0018 cut out.