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Cadillac 1961 390 v8

General Engine Building Discussion

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I’m wondering what is the best way to install press fit pins with new pistons?

also I have flat top followers when it comes to breaking these in is it true I have to hold it at 2000rpm for 20-30 mins straight away


Hi Matthew, fitting a press fit wrist pin is a little more tricky than floating. What you will want to do is freeze your wrist pins (a few hours in a freezer will suffice). You then need to heat the small end of the rod to expand it slightly to allow the wrist pin to be installed by hand. A gas torch or a butane torch is sufficient and will only require 30-45 seconds to achieve sufficient temperature. Care is required as overheating the rod will impact its strength. You DON'T want to heat the rod until it's glowing! You'll find it takes a couple of attempts to work out how much heat is required but once you get this sorted it's pretty straight forward. When you get it right the pin should easily slide through the rod by hand - No press required. You do only have a couple of seconds to work with this though so it's important to work fast and ensure your wrist pin is centred in the rod (same extension out each side).

With a flat tappet lifter you do need to follow the cam manufacturers break in procedure which normally involves keeping the rpm between 2-3000 for the first 20 minutes of operation. It's also important if you have a new cam that you use either new or refaced lifters. Used lifters can prematurely wear a new cam lobe.

As André said, freezing the wrist pins helps a lot, a freezer works well, as does dry ice, if you can get it. Overheating the small end of the rod can affect it's grain structure - old school technique is to put some oil or grease on the small end and when it bubbles it's hot, but not too hot.

Do some practicing beforehand for how you're going to do it, as you'll have just a few seconds to assemble them and if the wrist pin it too far, or not far enough, you'll need a machine shop to correct it.

If you're not sure, any competent engine shop should be able to do it for you for a few dollars.

Flat tappet camshafts and lifters rely on splash lubrication and an idling engine doesn't splash a lot of oil around - this is why the rpm is elevated, and why the correct lubricant MUST be applied to the camshaft lobes to prevent metal to metal contact before an oil film is established. Don't forget the distributor/oil pump drive, too. I also use an anti-scuff product on the pushrods, which should go back in the same positions, and orientations, they came from if re-used - rocker tips, and rocker balls, if the FE uses them.

It is strongly recommended you also use a running in oil with a high zinc, or other anti-scuff properties, to help the initial bedding in process.

André is correct, you should NEVER use old lifters unless you are SURE they are being fitted to the same camshaft lobe they came off, if re-using a camshaft, and they are in excellent condition with no wear that will make them concave.

I would disagree with the use of 'refaced' lifters/followers, though, for three reasons - the first is the new followers actually have a very slightly convex surface (if you hold a couple together, end to end, you will feel a slight rocking action) which corresponds to a very slight taper of the camshaft lobes which is normally ground on them. The second is they are often made with a chill-cast/hardened base and refacing may remove that. The third is some engines have a limit on the adjustment, or may even have none, and refacing makes the effective length shorter which can cause problems.

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