Cruisers & Sailing Forums (
-   Engines and Propulsion Systems (
-   -   Perkins 4-108 Rebuild Question (

bongo 29-02-2020 09:52

Re: Perkins 4-108 Rebuild Question
Thanks to all of you for your info on the rear crankshaft seal. It sounds like a job that I can handle. It will be nice to have dry diapers in the bilges!

rbk 29-02-2020 10:23

Re: Perkins 4-108 Rebuild Question

Originally Posted by bongo (Post 3084989)
Thanks to all of you for your info on the rear crankshaft seal. It sounds like a job that I can handle. It will be nice to have dry diapers in the bilges!

Mark the orientation of your fly wheel when you pull it. It only goes back on one way and depending on the location in your boat it can be a pain re-aligning while being in a pretzel.

donradcliffe 29-02-2020 10:46

Re: Perkins 4-108 Rebuild Question
For the OP, did you have any low oil pressure problems besides the oil leak? If not, the bearings are probably OK.

In my experience, the rear seal is not the only oil leak at the back of the engine. You will need to change out the old cork oil pan gasket as well.

bongo 01-03-2020 09:50

Re: Perkins 4-108 Rebuild Question
Thanks again for the input. Jpendoley, I sent you a pm asking for the copy of the relevant pages of the service manual, for the rear main seal. Thanks in advance!

jpendoley 05-03-2020 11:15

Re: Perkins 4-108 Rebuild Question

Originally Posted by Lepke (Post 3084079)
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.

Lepke-your post gave me courage, I learned how to pull liners- thank you. Maybe grew a few more gray hairs in the process...wound up running a very light weld bead up the liners to shrink them and they came out easily. No damage to the bore which measured close to the original spec-like within .0005 properly measured by a bore gauge.
Next question is about sleeves. Online I see lay people installing dry liners -and my originals are straight steel with no flange-but TAD told me the liners have to be bored after install. That seems odd as the originals were .0125 or so when installed new and they lasted 40 years. Thoughts from anyone who has lined a 4-108? Did you do it yourself or did you send it out? My machine shop is quoting 45 day turnaround and I will need to launched by then....
I'm trying to keep machine costs down and this might be a setback

Lepke 05-03-2020 11:32

Re: Perkins 4-108 Rebuild Question
For engines that don't come sleeved, rebuilding required boring the block and fitting a sleeve that usually has to be bored to a final size. The 4108s I've seen come with sleeves the proper size and honed with cross hatching and ready to install. The 4108 engine kit should come with sleeves with a proper bore. Mic them. I have a 1972 - 4108 on a 14kw generator I rebuilt a few years ago. Sleeves were standard and pre honed. The only fitting I had to do was minimal trimming the piston tops. The head I sent out. Depending on the kit you buy, they come with new valves, guides and seals that are sent with the head. Any auto machine should be able to do the head.
I had an old engine and an old kit. Newer engines kits may come with the piston tops the correct height. British machining got more precise over time.

jpendoley 06-03-2020 18:28

Re: Perkins 4-108 Rebuild Question
Thanks for that response Lepke. It has been interesting talking to parts suppliers and getting responses all over the map. Yesterday I spoke with a large very reputable Westerbeke/Perkins dealer who told me the notes have to be rebored and the liners bored. Parts4Engines which sells lots of 4-108 kits agreed. My local Napa disagrees and says they can source the correct sleeves that should need no boring. And this is boring not simply honing. Pretty big difference of opinion. For my money ( of which I have precious little), Im going with the Napa folks. These engines powered everything from industrial reefers to field tractors. Were not building a race car. I like the 4-108 for its virtues: simplicity, rebuild ability and ubiquity. I will let the forum know how it all turns out.
Thanks again for the insight to j hi ou and everyone else who contributed suggestions.

All times are GMT -7. The time now is 14:08.

Powered by vBulletin® Version 3.8.8 Beta 1
Copyright ©2000 - 2020, vBulletin Solutions, Inc.

ShowCase vBulletin Plugins by Drive Thru Online, Inc.