: Rebuilt engine with knurled pistons
Oct 9th, 10, 11:39 AM
About 20 years ago, I had my 327 rebuilt by a local machine shop. At the time it had .040 over pistons that were in good shape, but they had to bore the block .060 over. I recall them asking me how much I drove the car and at the time, I drove it maybe a few hundred miles a year. They knew that I didn't have a lot of money to spend on the rebuild, so they suggested that rather then buy new .060 over pistons, they could knurl my existing pistons and I should be good for about 30,000 miles. That sounded like more miles than I would ever drive the car back then and not having much to spend I told them to go ahead, so they went ahead and glass beaded and knurled the pistons and put in new .060 rings.
I probably have about 6000 miles on that motor and am driving it now around 2000 miles / year. I don't race it, I just mainly cruise in it, getting on it every once and a while. The motor still runs great. It doesn't burn any oil and the compression numbers have been consistent each year.
Does 30,000 miles sound like a reasonable estimate for this rebuild? Should I expect any symptoms other than burning more oil or lower compression numbers as it reaches the end of it's life ( which hopefully is still about 10 years away)? If/when I do change the motor, I want to be able to plan ahead and do it over a winter.
Oct 9th, 10, 01:01 PM
I think if you are already 60 over you will want to get a different block when you are ready for a refresh. Might as well plan on getting pistons that fit what ever block you are using. Piston slap noise might be the early indicator of it reaching it's live I would think on your knurled pistons.
I'd just start from scratch and build a short block, then reuse the top end if you want to / like the parts combo.
Oct 10th, 10, 04:31 PM
Thanks! Actually, when the time comes I will probably get a crate engine.
I have never heard piston slap, but I guess I'll recognize it if it happens. Hopefully I'll be OK for a few more years though.
Oct 10th, 10, 04:34 PM
did you get the valve guides knurled at the same time?
i love the old school ways of doing things..
1969 RS/SS DROPTOP
Oct 10th, 10, 04:34 PM
I've heard of knurled guides but not pistons??
Oct 10th, 10, 04:41 PM
No knurled valve guides. They resurfaced the heads, installed new valve guides and did a valve job. ( luckily I still have the receipt from 20 years ago to refresh my memory).
Oct 10th, 10, 05:28 PM
Are you sure they bored the block to .060, or did they just knurl the pistons to tighten them up a bit at .040 and leave the block alone ? I have never heard of knurling pistons enough to go .020 oversize, not even sure if it is possible. One of my customers has a piston knurler and I have seen a few over the years, but usually it is only done to keep from boring the block.
All that being said .... if it runs good, has good compression and does not use any oil, it will probably last a long long time.
Oct 10th, 10, 06:41 PM
I've just learned something new. :D I'll have to look this up as I am interested in how this is done.
Oct 10th, 10, 09:30 PM
Burning oil will be your first symptom. I wouldn't worry about it as long as it's running good and not burning oil. You still may have another ebuild in that engine yet. As bill said I bet they didn't bore to .060 they just snugged up your current pistions. Run it and enjoy it.
Oct 11th, 10, 05:29 AM
To be honest, I don't really remember that they bored it to .060, I'm just going by memory and the receipt. I know that the block had been previously bored .040 over and had .040 over forged pistons.
The receipt includes the following:
- glassbead pistons
- knurl pistons
- parallel block decks
- plate hone cylinders
- new .060 over rings
So based on the .060 over rings, the knurled pistons and a vague recollection of them asking how much I drove the car to help decide if I could reuse my old pistons, I assumed that it was bored over .060. Since they didn't charge for a boring, just honing, it looks like you may be right.
Would this make sense? Can you put .060 rings on .040 pistons where the cylinders were just honed? Maybe I am in better shape than I thought!