resized rods. face has dings

[twostick]

For a stock application, those nicks are not an issue.

If this was a full tilt race application, theoretically, a crack could start at one of those nicks and cause a failure. Odds on the Lottery are probably better than that scenario tho.

Some machinists as has been commented on here, are hung up on too much side clearance being a problem and are reluctant to increase it to clean up stuff like you are seeing.

The only side clearance spec that you need to worry about, is minimum clearance. Without going to silly extremes, there is no such thing as too much.

Kevin

 

[Big_John]

Some machinists as has been commented on here, are hung up on too much side clearance being a problem and are reluctant to increase it to clean up stuff like you are seeing.

There's a lot of years of engine builders warning against too much side clearance. I had always heard and read that too much clearance would drop oil pressure and spray more oil on the cylinder walls.

I've seen that has been dismissed as not that important as we all used to think it was and I can tell you from personal experience that I've run engines with more side clearance than spec'd with no problems.

As you say, as long as it's not "silly extremes". Cleaning up the sides of the con rod shouldn't be enough to worry about, but if I had a rod that needed a lot of the side faces machined off to get it straight, I'd probably toss that rod and find another that didn't need that much. Of course, IMHO, that is just common sense for any engine build.

Of course, there's a lot of schools of thought on con rods and engine rebuilds in general... Some guys wouldn't go to the expense of rebuilding the con rods for a street engine and some guys will replace rather than rebuild. I've seen engines tossed together in a dirt floor garage from odds and ends that ran as well as something a pro built in a clean room from the best parts, so I'm a bit cynical about a lot of it.

I wanted a good source of info on this and googling came up with this. I like that they quote my favorite engine building book, written by Bill Jenkins. The Great Rod Side Clearance Imbroglio: Clearing Up the Confusion

This is really interesting stuff (at least to me LOL) but I can't help but think that in this particular engine build, since it's his first, it's probably best to keep everything close to stock specs that we know will work in the long term.

 

[twostick]

The reason excessive side clearance causes oil pressure and windage issues is a myth is because the bearing clearance is what dictates the amount of oil "leaking".

You have a .0015" - .002" gap feeding a .030" - .040" gap. That's like feeding your garden hose into a fire hose. It's not making you fill a bucket any sooner.

Kevin

 

[Big_John]

The reason excessive side clearance causes oil pressure and windage issues is a myth is because the bearing clearance is what dictates the amount of oil "leaking".

You have a .0015" - .002" gap feeding a .030" - .040" gap. That's like feeding your garden hose into a fire hose. It's not making you fill a bucket any sooner.

Kevin

The question that I haven't found an answer for is "how much is too much for a stock type piston with a pressed pin?". Or with a floating pin for that matter. And I'm not talking about oil control, just how much excessive side clearance could affect bearings or pin bores. I guess you could say it's more of a geometry question that looks at side loading more than anything else.... and it may not come into play at all.

I know that race engines will use a piston guided con rod where the side to side clearance of the rod in the piston is limited. That would keep it all from rattling around too much... But I don't know as that's practical in the old design street engines we run or cost effective for that matter.

Interesting stuff!