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Old 23-07-2014, 14:11   #1
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Finding a Mechanic to Diagnose a Perkins - Mid Chesapeake

I have a Perkins Prima M50 at 3,600 hours with several issues that are starting to impact its reliability. I have not had much luck finding a mechanic willing to diagnose / work on this engine and have gotten much conflicting advice.

In the spring the engine was smoking (blue-gray) heavily on startup and putting a small amount of unburnt diesel in the exhaust water. I had the injectors rebuilt and this seemed to take care of the diesel in water situation but did not resolve the smoking. Since then, the engine has been getting harder and harder to start. Strangely, when it was fifty degrees ambient (before the injector rebuild) it would start right up but now that it is warm out it is difficult and seems to be getting worse.

I’ve had varying advice to rebuild the injector pump, replace the piston rings, replace the valve guides, or re-bore and replace the pistons. Alternatively I have been told a 3,600 hour engine probably doesn’t need rings or piston work but may have glazed cylinders. I have also been told I shouldn’t sink another dollar into this obsolete 21 year old engine and should simply repower. Other issues include the Hurth transmission being due for a rebuild or replacement, the timing belt needing to be replaced, and the glow plugs needing replacement.

I don’t have time or the knowledge to troubleshoot all this myself. I might be able to put 25% or less of the cost of a repower into this engine and get a lot more hours/years out of it, but I don’t want to spend twice that figuring out where I should have spent the first half! Does anyone have a recommendation for a good diesel mechanic in the Baltimore/Annapolis area?

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Old 23-07-2014, 14:26   #2
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Re: Finding a Mechanic to Diagnose a Perkins - Mid Chesapeake

But I'd start with glow plugs, they are real easy to check with a multimeter without spending a nickel

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Old 24-07-2014, 03:33   #3
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Re: Finding a Mechanic to Diagnose a Perkins - Mid Chesapeake

Glow plugs are known to be burnt out but were also known to be burnt out when the engine started instantaneously without them in 50 degree weather.
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Old 24-07-2014, 06:45   #4
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Re: Finding a Mechanic to Diagnose a Perkins - Mid Chesapeake

Speak to Rob Nixon at Dependable Marine Services. Ph: 443-450-4886 or Scott Segal at AR Marine, Ph 410-721-6025.

Both are good mechanics and ar reliable and not prone to BS. Both are in Annapolis.

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Old 25-07-2014, 15:22   #5
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Re: Finding a Mechanic to Diagnose a Perkins - Mid Chesapeake

This probably won't be of any use to the majority of you but here's how you troubleshoot it:

First, the only way that I know of to reliably check the rings and valves is to do a leakdown test on a WARM engine if possible.

A leakdown test is similar to, but different from a compression test. It uses compressed air from an air compressor or it could be from an air tank--It doesn't make any difference.

The leakdown apparatus consists of the leakdown gauge assembly and an adapter to fit your engine (it replaces each fuel injector one at a time).

Now you EITHER need to find someone with both a leakdown tester AND an adapter to fit into your particular fuel injector ports, OR you can build your own with parts from McMaster-Carr Industrial Supply (my best friend!).

The leakdown adapter: I found somebody on the internet a year or so ago who sold the adapters for my particular engine (4.107) but they were expensive and I'm cheap so I made my own. I machined my adapter to have the same lower dimensions as my fuel injectors. Any machine shop competent or not can do this if you don't have access to a metal lathe. I put a quick disconnect (like the ones used for disconnecting air tools) onto the upper end of the adapter.

The leakdown gauge assembly: is easily fabricated using parts from McMaster-Carr as mentioned above. Instructions for making one are on YouTube. I did it and it's very easy.

Or you can just buy one...but like I said, I'm cheap.

So the leakdown adapter gets installed in place of one fuel injector (say #1). Leave all the other injectors in place so that the engine won't turn over from the air pressure. Use a new or annealed copper sealing washer. Directions for annealing copper washers is available on the internet. Very easy to do with one of those Burnz-O-Matic yellow MAP torches.

Next, rotate the crankshaft until the #1 piston is at Top Dead Center on the compression stroke (intake and exhaust valves both closed). If you don't already know how to do this you just remove the rocker cover and rotate the crankshaft until both #1 rocker arms are loose.

Next, you hook the leakdown gauge assembly up to the air source (the compressor or the tank) and adjust the knob on the gauge assembly until the gauge reads 100psi. You obviously need to have more than 100psi in the tank or available from the compressor in order to get 100psi at the gauge (more on this below).

Finally, plug the leakdown gauge assembly onto the installed leakdown adapter. Any leakage past the rings or valves will result in a something less than 100psi reading on the gauge. The reading will be directly proportional to the leakage, but won't by itself tell you what's leaking. That's where the magic is... (below).

By the way, there is nothing magical about 100psi. If you can only get say 90, then go with it. 100psi is used so that people can talk about things like "5 percent leakdown" which is 100psi at the gauge when it is un-plugged from the adapter and 95psi when plugged in. If you can only get 90psi at the gauge then if you get 85psi on the gauge when plugged in you've got 5.5 percent leakdown (90-85 = 5; 5/90 = 5.5%).

But don't use 20psi or something. You want the air pressure to really push against the valves and the rings.

Now for the "magic" part: Take a McDonald's soda straw--no other brand will do (just kidding), put one end to your ear and the other end into the dipstick hole. If air is leaking past the rings you will be able to hear it--it will be obvious.

Then do the same thing for the #1 intake and exhaust ports. If either or both are leaking you will be able to hear it.

The louder the noise the more leakage.

After you're done with #1 AND YOU'VE WRITTEN EVERYTHING DOWN rotate the crankshaft 180 degrees, reinstall the #1 injector, install the adapter in the #3 port (for a four cylinder). Our imaginary engine here fires 1,3,4,2. Other engines may have different firing orders...

Repeat the process for #3, then go on to #s 4 and 2.

And FWIW, you can also diagnose inter-cylinder head gasket failures by listening in the intake and exhaust ports of adjacent cylinders. Obviously no air should be intruding into the adjacent cylinder ports.

Easy as pie!

Ps: You can also do this with a cylinder head that is not installed on an engine to check valve sealing BEFORE installing it on the engine. You just need to make a plate with an o-ring seal that will fit around the combustion chamber and drill four holes in the plate to match the head bolt holes for that cylinder. I NEVER rely on the isopropyl alcohol or water leakage test to tell me how good my valve job is...

Just sayin'...

Jeez, I wrote a freakin' book...

Ray Russell
Valiant 40 #163
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mechanic, perkins

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