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Old 07-04-2016, 19:36   #1
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Perkins 4-108 swap questions

I have an Allied Princess 36 with a blown Perkins 4-108. The engine has been removed and I have another candidate 4-108 block available that came out of a genset.

Is there any reason I can't just swap the accessories, bellhousing and tranny from the old one to the new one and drop it back in?
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Old 07-04-2016, 20:26   #2
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Re: Perkins 4-108 swap questions

Depends on what "blown" means...

Would you rebuild your own engine if new parts were available and amazingly cheap?
Because they are

Last time I checked a complete rebuild kit was around 350 and a new crankshaft was another 350.

Wish I had a 4-108. A piston on mine is in the hundreds.

http://www.parts4engines.com/perkins...-overhaul-kit/
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Old 07-04-2016, 22:02   #3
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Re: Perkins 4-108 swap questions

Blown means a rod through the crankcase. I was going to swap parts and drop the new one in as a short-term solution to getting her seaworthy enough to move her, then do a refit at a cheaper, DIY yard.

Yeah, the rebuild kits are about $550 for everything. If the shaft mics out ok, I might do a polish and back in she goes.
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Old 07-04-2016, 22:39   #4
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Re: Perkins 4-108 swap questions

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Originally Posted by synclavier View Post
Is there any reason I can't just swap the accessories, bellhousing and tranny from the old one to the new one and drop it back in?
the short answer is no. I've done short blocks in cars with no problems. I think the difference between the various 4108 version is in the accessories.
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Old 08-04-2016, 11:16   #5
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Re: Perkins 4-108 swap questions

do a comparison and make your decision based on measurements you have made. I have a spare 4108 and the blocks are identical in every respect, 10 years difference in manufacturing dates. I have swapped out many parts, so I think its very possible. also my Perkins shop manual does have a cross reference for replacement parts.
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Old 08-04-2016, 11:33   #6
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Re: Perkins 4-108 swap questions

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the short answer is no. I've done short blocks in cars with no problems. I think the difference between the various 4108 version is in the accessories.
Don, I'm not sure what you mean? If the difference is only the accessories then... yes ... right?
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Old 08-04-2016, 11:35   #7
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Re: Perkins 4-108 swap questions

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Originally Posted by synclavier View Post
I have an Allied Princess 36 with a blown Perkins 4-108. The engine has been removed and I have another candidate 4-108 block available that came out of a genset.

Is there any reason I can't just swap the accessories, bellhousing and tranny from the old one to the new one and drop it back in?
I would just look closely at the various attach points, especially the flywheel/plate/bellhousing area. It seems I've heard of differences in that area? but not sure really....
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Old 08-04-2016, 12:04   #8
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Re: Perkins 4-108 swap questions

It works just fine. I did exactly what you are proposing with one small difference. I replaced a 4107 with a 4108 that had powered a compressor. I gained the advantage of glow plugs and eliminated the old hot start system. The conversion was done in1999 and it's still going strong.
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Old 08-04-2016, 12:13   #9
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Re: Perkins 4-108 swap questions

The 4-108 was built in at least 18 countries and has powered every conceivable device that required a lower horsepower, reliable diesel. The basic blocks are the same. The difference is in the parts used for marinization. Before you do anything, have you diagnosed the reason that the rod came through the block. Sounds like it could be an oil pressure (or lack therof) problem. If the replacement block is from a running take out, then you are probably OK. THis is also a good time to clean and inspect the heat exchanger, the damper plate and the motor mounts (relatively cheap and easy to replace).
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Old 08-04-2016, 12:31   #10
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Re: Perkins 4-108 swap questions

Do you know for sure what caused it to throw the rod - and what else needs replacing?

ie what Captain Bob said Jeez, did it really take me half an hour to write a sentence? Duh...
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Old 08-04-2016, 16:22   #11
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Re: Perkins 4-108 swap questions

Not sure about the Perkins but some generator motors have "fixed" fuel pumps /governor to maintain EXACT revs for either 50 or 60 Hz.
Might need to swap out the injector pump?
My Westerbeke has an independent belt driven governor.
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Old 08-04-2016, 17:08   #12
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Re: Perkins 4-108 swap questions

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Originally Posted by Cheechako View Post
Don, I'm not sure what you mean? If the difference is only the accessories then... yes ... right?
If you read the question the way it was written, no means there is no reason it can't be done...
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Old 08-04-2016, 22:22   #13
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Re: Perkins 4-108 swap questions

I assume that it threw a rod due to oil starvation, but I'm not exactly sure why that happened. The boat yard pulled the engine without my being there, so I haven't gotten a closer look yet. Thanks for the replies.
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