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Cam break-in needed, or not?

Practical Engine Building

Relevant Module: Engine Break In > Engine Break In

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Hi all!

Still have a question about the engine breaking in process, more specifically on the cam part of this.

Context :

My new engine has what we can call flat tappet style lifters (1999 Mazda Mx5 NB head, so it's DOHC with mechanical "above bucket" shims style lifters), and I'm not exactly using fresh new cams and lifters...

At first, I'll be running a quite ordinary exintake mod, which means that the camshafts I'll be using are well beyond the point of needing any breaking-in (let's say they have both seen between 100.000 and 150.000km of use before), and it's the same deal for both the lifters and MOST of the shims.

So yeah, IMO I should not need to follow some cam breaking-in process whatsoever on this setup, right?

However, here is my concern:

It is to know that, during the valve clearance adjusting process, I reused a bunch of old shims I had for this engine type, but ALSO some brand new shims that I had to purchase spot on. Some are genuine Mazda, some are aftermarket ones with a different surface finish as it seems, and I also indeed grinded a part of the shims (including some of the new aftermarket ones) to my specs as needed.

So... do you think I should consider to take some precautions whith the initial start-up / breaking-in process of this engine (also using moly lube onto the shims => currently engine assembly lube), or is it all good cam wise and those new shims are not something to take into account on this matter?

Thanks in advance for your advises, as I'm currently no gold member I think I could not answer back on this thread before next time I'll be GM, but please be sure I'm all grateful for any help :) !

Personally, I'll always use some form of anti-scuff lubricant when replacing any parts in the valve-train. They have a direct oil feed, and "shouldn't" need it, but old habits die hard.

If it's the same process as for the Suzuki M series engines*, the shims should be fitted with the ID/size markings to the valve, and any material removed should have been on that side.

I really dislike swapping used shims around, especially on higher mileage engines, as the normal wear will be to "cup", or wear the middle of, the shim and slightly round off the cam' lobes, but sometimes...

*I took my Sport to the dealer because the tool was over NZ$500, and a set of shims was, IIRC, NZ$1800 - it would seem they were 'less than competent' as it's got a 'tappet' noise that comes and goes - I suspect an unevenly worn shim, and will be checking as I also need to replace the 15yo original cover gasket, that they re-used and is leaking.

It would probably have been cheaper to buy the tool and shims, and on-sell when done - and it would have been done right.

Good info from Gord as usual.

In terms of how you treat the engine when ready to run it, I'd get it up to full operating temperature, run it at 2000-2500 RPM for a minute or few minutes (opinions vary), shut it down, inspect the oil filter after opening it up with an inspection tool. See if there's any concerning debris. If not, change the oil and filter.

Beyond that opinions will vary. Some will say it's ready to send it, others will suggest avoiding high RPM for a period of time or other constraints.

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