Perkins 4.108M DIY Rebuild -- A Narrative - Page 6 - SailNet Community
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post #51 of 268 Old 01-07-2013
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

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Thanks for convincing me that I should never try this!
Anyone who enjoys doing their own work on boats, cars etc. should do it at least once. I built a high performance Chevy engine for my wife's car 20 years ago and it was a source of endless satisfaction - from seeing it completely dressed on the engine stand to the first time I lit it off to every time I stood on it afterwards.

The first time it lights is absolutely exhilarating.
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post #52 of 268 Old 01-09-2013
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

Great series! Can you fast forward to the part on replacing the rear main seal?


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post #53 of 268 Old 01-09-2013
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Wink Re: Perkins 4.108M DIY Rebuild -- A Narrative

Por: Great narrative! I have an old 4.107 - nearly the same engine, but not anywhere near the number/range/choices for repair/overhaul parts that you have!

Glad to see that you are biting the bullet and having the machine shop do the valve guides and machine (grind) the valve seats. Whenever you replace valve guides (or even take the head off for that matter) it is always a good idea to have the valve seats professionally ground. Notice - I said ground, NOT lapped. Lapping valves into seats has pretty much fallen out of favor in the diesel world (I was a diesel Chief Engineer on oil tankers for 30 years). Standard practice now is to grind the seats, then "blue" (check) the seating of the new valves into the new seats. Grinding ensures accurate concentricity of the valve to the seat - lapping can damage that concentricity. New valves/seats will also "wear in" to a certain extent when the engine is run and everything heats up.
The bottom line is: since you have everything apart, now is the time to do the job as best as you can (including replacement parts) - as long as your wallet holds out! Thanks again for sharing your experience!
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post #54 of 268 Old 01-09-2013
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

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Great series! Can you fast forward to the part on replacing the rear main seal?
The rear main on a 4-108, has a spiral cut on the crankshaft, to pull oil back in as the engine rotates. So it is actually designed to leak... to get it to stop leaking, or slow it, you need to ensure crankcase vacuum, from the valve cover to the air intake.

Why, why, why?
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post #55 of 268 Old 01-12-2013 Thread Starter
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

Anyone still interested? Hope so...

Got a call late yesterday that the machine shop's done with the block and head; I'm going to pick them up Monday. I stopped by earlier in the week just as they were getting done doing the finish honing of the new cylinder liners, and I gotta say after the initial hot tank the block looks pretty good.

After way more hours than I'd care to admit, I'm getting close to the point that I can start painting.

I am, though, faced with a decision or two -- which I hope some of you will be able to assist me with.

As I mentioned in an earlier post, many of the bolt-on parts of this engine are aluminum. I really, really want to get a paint job on this this that will last. With that in mind, I've been researching my options:

- Engine primer.
- Self-etching primer.
- Zinc chromate primer.
- Epoxy primer.
- Alodine, followed by one of the above primers.

It could very well be that I'm overthinking this, but I'd love to hear what you folks would recommend.


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post #56 of 268 Old 01-12-2013
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

Porfin- great thread, nice that you are taking the time to share with everyone.
I'm no expert on priming aluminum, but when I talked to a reputable auto paint store about it they said the only way to go is the self etching. I used it on a part I made (5086 alum. IIRC) and top coated with an automotive paint and it looks as good today as it did 5 years ago when I made them. That said, I've also had excellent results on aluminum sterndrive props with the zinc chromate spray primer (Moeller?).
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post #57 of 268 Old 01-13-2013
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

I'm a fan of Zinc Chromate on aluminium. I've never had a finish lift when it was on top of ZnCrO4. I've never put it on anything that got really hot though.

It's the standard coating on aircraft internal structures so it can take ultra cold but, as I say, I don't know about hot.

I presume you are referring to things like the heat exchanger tank, thermostat housing & so forth? If so, they should be no problem. Anything close to the exhaust ports or manifold could be though.

One tip I learned the hard way - don't paint the major parts individually before assembly. I did that once and ended up with small areas that were exposed with no paint on them. Bits of the block deck that the head didn't cover and so forth.

Once you have the long block assembled, paint it and then put the hoses, clamps etc. on so they don't get covered in paint the way the factories do.

You also don't want paint in the grooves of your pulleys or they can slip. A trick for painting them is to hold them with an old V-belt in the groove while you spray them.
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post #58 of 268 Old 01-15-2013
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

Porfin, I haven't heard any talk of valve stem seals. Does this engine use them? In my experience leaking valve stem seals can cause the mess you had, especially the coating on the valves and oil in the exhaust.

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post #59 of 268 Old 01-15-2013
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

PorFin - another tip on painting the engine - don't paint it Perkins blue, do it white instead. It shows up leaks right way and makes them easy to trace. It also brightens up the engine compartment which I presume is the usual gloomy hole.

See the before & after of my last engine.
Attached Thumbnails
14b Engine before.jpg   15d Engine after.jpg  
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post #60 of 268 Old 01-15-2013
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

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Originally Posted by SloopJonB View Post
PorFin - another tip on painting the engine - don't paint it Perkins blue, do it white instead. It shows up leaks right way and makes them easy to trace. It also brightens up the engine compartment which I presume is the usual gloomy hole.

See the before & after of my last engine.
That white looks really nice.
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