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Old 27-02-2020, 07:38   #1
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Perkins 4-108 Rebuild Question

Looking for some advice from experienced rebuilders...
Have the engine broken down to bare block. Was hoping to just reseal it, but after removing the pan it became clear that a limited rebuild was in order. For all of you cold weather sailors remember you heard it here: DON'T USE STARTING FLUID-even sparingly- to start your diesel. One ear of number four piston skirt was lying in the pan. I am certain starting fluid was the culprit. At that point, I needed to remove the piston, so off with its head! I now have it down to a bare block and am astonished that other than the broken skirt and and some pitting on the number three piston head (errant injector tip?) there is no apparent wear on the liners-not a scratch-they shine like mirrors-the bearings, the valves, the seats, journals on the crank and cam-all look like new.

So I am looking for a little guidance on machine shop/next steps...
I have the block stripped. Crank and cam out, pistons and bearings all separated, bagged and labelled as to original locations and orientation etc. Head obviously off. I have been meticulous and I have the shop manual. I bought a set of decent micrometers and a dial bore gauge and learned how to use them-which was actually fun. The numbers suggest the cylinders (dry sleeves) are really not too worn-perhaps 3.127 or 3.128 when the spec is 3-125-3.126. So at most .002 out. Some ovality, but not extreme. No scoring on the sleeves and very little carbon at the tops of the sleeves-very slight ridge.
The crank seems brilliant-no scoring-no pits almost looks freshly ground and it seems to measure completely within spec. Bearings were spotless. One piston had a broken skirt (found it in the sump-but did not migrate) and one piston top had some pitting where it looked like an injector tip bounced around the combustion chamber)
Rebuild kit is $600. Includes pistons, rings, bearings etc. You can spec oversize if the crank had to be turned.

My question is this: is it likely I just need sleeves and the block milled? I'm still practicing my micrometer skills-but last night the crank journals "miked" at exactly the manual spec (2.248/2.2485). The shop notes mention 4-108 cranks were Tuffrided-but the machine shop says that is no longer done due to toxic concerns. Apparently Tuffriding created a harder crank surface-maybe that explains the lack of wear on the journals. The dial bore gauge revealed some wear and ovality in the sleeves as mentioned- the shop manual also states the head can not be milled, but it seems dead flat. Valves not miked yet, but no observable pitting or burn. I am thinking I may just need to have the block sleeved, reinstall the crank with the original size bearings and be good to go. What are the thoughts of the group?
I am trying to avoid a monster machine shop bill...do I trust my micrometer skills or pay them to measure everything in addition to sleeve installation? What have I neglected to consider??
The machine shop is quoting a 6 week lead time-that will make my schedule tight, but not impossible...
Jim
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Old 27-02-2020, 14:38   #2
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Re: Perkins 4-108 Rebuild Question

What was the engine doing that caused you to take it apart?

If you plan on keeping the engine for a long time, you'd be ahead to do a full rebuild.
The problem with a 4108 rebuild is the pistons are made to be fitted. See the manual. The engine is assembled and the height of the piston to the top of the block is measured. Then the pistons are removed and the tops machined as necessary to have the proper distance. British machining methods of the time were loose. Many things made in Britain need hand fitting. I know of people that used the pistons as delivered without measuring or machining. Some were ok and some had clearance problems. For some where the engine would run, had too high compression problems that caused head gasket and other problems.

You can do a cheap rebuild using the bearings you have now if they show little wear. At the bearing install stage, check them with Plastigauge. Available at most auto parts.
The sleeves should be lightly honed with a proper hone and drill - you could do that. The good pistons will work, you'll need new rings and the carbon removed from the sleeve tops or you'll damage the new rings. I don't know where you can find a single piston. Post a pic of the piston you have, maybe it's usable. I doubt the starting fluid caused the piston to lose part of it's skirt. Usually it blows holes in the piston top, down the side of the piston, and breaks rings. The piston probably had a casting flaw. You might find a used piston on eBay.
So in a cheap repair you need gaskets, rings and maybe bearings and a piston. The head could be used as is.
But if it was my engine, I'd do a full rebuild.
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Old 27-02-2020, 15:57   #3
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Re: Perkins 4-108 Rebuild Question

x2 What Lepke said. You've got it apart why put old components back in, bearings are cheap. I will also add to take all components to a local auto shop and have them jet wash components overnight, then inspect closely for any wear or cracks. Probably cost less than $100 and save many, many hours of hand cleaning of which wont come close to a good jet wash. If you havent already look at Parts4engines they have good prices and reasonable shipping. I have ordered many parts from them with great success. Good luck
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Old 27-02-2020, 16:20   #4
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Re: Perkins 4-108 Rebuild Question

Having done over 200 Perkins 4.108 rebuilds in the last ten years:
-We take the engine apart, examining wear as you are doing.
-We take the block & head to a machine shop we have been using for years
-They put the block & head in an oven, heating it for 24 hours to 500 degrees, looking for cracks and plane. It also comes out whistle clean. As it is cooling they press in new cylinder sleeves. They grind the valve seats.
-We bring it back to our shop & install NEW pistons, rings,valves, valve springs bearings, seals gaskets. I have rebuilt, tested and calibrated the fuel injectors. We send the high pressure pump to a local shop that specializes and has the $20,000 machine for testing
-The engine is carefully re-assembled following Ma Perkins specs.
-After 3 coats of high temp primer & 3 coats of Perkins blue it is rolled out to our test bed and run for one hour, observing ease of starting, oil pressure, temp, smoke color etc.
-Then it is sold for $6,995 & a re-buildable core or $1,500 core charge.
-More info on request
-We have two rebuilds ready to ship
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Old 27-02-2020, 18:38   #5
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Re: Perkins 4-108 Rebuild Question

No intention of putting out of spec parts back in.Definitely sleeving, valves and seats and maybe turning the crank. That means dropping a bearing size. Mostly looking for a heads up on the machine shop gotchas. Lepke, I did read in the forty year old manual about the need to dress new pistons-was kind of hoping the aftermarket found a way around that by now. Thanks for the reminder though.
And OldCalSkipper-your rebuilds are attractive, but for me its the devil I know-that and I think I can get all done for $2000 if I do her myself-plus I will know my engine inside out.
Thanks everyone for the advice!
Jim
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Old 27-02-2020, 18:49   #6
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Re: Perkins 4-108 Rebuild Question

Lepke-you asked why I tore it apart-it was leaking oil at an incomprehesibly high rate. Two cups a day! I had planned on just resealing until I found the broken piston skirt. Once I saw that and I had one piston out seemed to make sense to remove them all and mic the crank. In for a penny in for a grand. Engine has prolly 5-6 hours on it (came with a dead meter). For all the leaking oil-absent the broken skirt it looks almost new inside.
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Old 27-02-2020, 21:21   #7
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Re: Perkins 4-108 Rebuild Question

Quote:
Originally Posted by oldcal46skipper View Post
-We have two rebuilds ready to ship
Sent you a PM
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Old 27-02-2020, 21:26   #8
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Re: Perkins 4-108 Rebuild Question

I doubt the crank needs turning. I've mic'ed hundreds of diesel cranks and if no oil failure occurred they are usually close enough to original that standard bearings do the trick. If the crank is worn, then I have it hard chromed to spec. Then it never wears. Most diesel cranks have hardened journals. If turned, that's removed. Not all small crank turners know how to hard surface.

You should be able to mic ok.
Rear main usually leaks on a 4108 with the original rear seal. Old rope seal needed to be soaked in oil and lubed with grease before install. New ones no, but I grease them to prevent the crank from pulling the seal out of position on the first start. You can buy the new seal at parts4engines at about 1/3 of what Foley charges including shipping.
On ether, I've been using it for 60 years w/o problems. Don't use more than needed, don't run an engine on ether. You can use it every day w/o damage on a hard to start engine if you don't use too much.

You can change the sleeves yourself. I'd send the head out for a rebuild and either send out the injectors or buy new nozzles.
I have a 1972 - 4108 turning a 10kw at 1800. Only rebuilt once, by me. Now it's like new and still has a standard crank. My 1947 Detroits have original standard cranks.
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Old 28-02-2020, 08:04   #9
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Re: Perkins 4-108 Rebuild Question

Lepke-great feedback thank you. everyone has been really generous about giving advice and tips-that's the best part about the forum. Another question: you mentioned I could install the sleeves-but they are a dry inteference fit-doesn't that require a huge press?
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Old 28-02-2020, 11:45   #10
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Re: Perkins 4-108 Rebuild Question

I hope this isn’t hijacking this thread, but it appears to have posters that have extensive knowledge in this area. I have a Westerbeke 40-108, (so the block is essentially a Perkins 4-108). It powers our ‘78 Valiant 40 through a Paragon transmission and a Walters V-drive. I have pretty good access to the V-drive end of the engine, (which is obviously the forward end). The engine only has 1200 original hours on it, and it runs like a top. EXCEPT for the rear engine seal, adjacent to the tranny. It drips continuously, and it is virtually impossible to get a “Kings Point Gasket”, (drip pan), under it. I change “soiled-diapers” every day or two. There does not appear to be excessive crankcase pressure. Needles to say, I’d like to replace the seal. The boat is in the water and we have a PSS dripless shaft seal, and I know that I’ll have to support the shaft to keep the water out. I have had the V-drive off once. I believe that getting the tranny off wont’ be too difficult either. I don’t believe I can pull the oil pan without lifting the engine, which will be a chore, but, is probably doable. So, my question: What is required to change out this rear crankshaft seal?
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Old 28-02-2020, 12:22   #11
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Re: Perkins 4-108 Rebuild Question

Quote:
Originally Posted by bongo View Post
I hope this isn’t hijacking this thread, but it appears to have posters that have extensive knowledge in this area. I have a Westerbeke 40-108, (so the block is essentially a Perkins 4-108). It powers our ‘78 Valiant 40 through a Paragon transmission and a Walters V-drive. I have pretty good access to the V-drive end of the engine, (which is obviously the forward end). The engine only has 1200 original hours on it, and it runs like a top. EXCEPT for the rear engine seal, adjacent to the tranny. It drips continuously, and it is virtually impossible to get a “Kings Point Gasket”, (drip pan), under it. I change “soiled-diapers” every day or two. There does not appear to be excessive crankcase pressure. Needles to say, I’d like to replace the seal. The boat is in the water and we have a PSS dripless shaft seal, and I know that I’ll have to support the shaft to keep the water out. I have had the V-drive off once. I believe that getting the tranny off wont’ be too difficult either. I don’t believe I can pull the oil pan without lifting the engine, which will be a chore, but, is probably doable. So, my question: What is required to change out this rear crankshaft seal?
Tranny, damper, bell housing, fly wheel and adapter plate all have to come off. Get a new age rope seal.
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Old 28-02-2020, 12:53   #12
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Re: Perkins 4-108 Rebuild Question

One wonders if there is no cylinder wear, why sleeve it? Lightly hone and new rings, and of course at least one new piston. No journal wear, why not just new bearings? On cars, in the old days that was an "overhaul" as opposed to a "rebuild".
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Old 28-02-2020, 16:57   #13
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Re: Perkins 4-108 Rebuild Question

Bongo: If your Westerbeke is a 4108, this is the seal:
https://www.parts4engines.com/perkin...l-upgrade-kit/
About $31 and I've found their shipping rates reasonable.
You don't need to remove the pan unless you're changing that gasket because of leaks.
With the transmission and flywheel out of the way, the rear main seal is in a removable housing that slides off the crank. You replace the seal in the housing, grease it, slide into place and then bolt everything back together.
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Old 28-02-2020, 17:48   #14
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Re: Perkins 4-108 Rebuild Question

I just replaced my Seal two years ago. It can be done in place and if the leak can be stopped. I have the shop manual if you’d like me to copy the relevant pages I could do that.. You also can find a couple of articles on the web about the process.
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Old 28-02-2020, 18:49   #15
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Re: Perkins 4-108 Rebuild Question

Just did mine a few months ago. The parts4engines seal is the one I went with as well. The adapter plate for the bell housing also had to come off but other may be different. I also did it with the engine in place. Not too bad. Have a good block and tackle for the tranny and an extra set of hands is nice but I did mine alone, just had to use more words
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