Perkins 4.108M DIY Rebuild -- A Narrative - Page 19 - SailNet Community
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

PorFin,

Where did you find the piston-to-liner clearance value for your engine? I've been over my manual twice with no luck...

Ray R
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

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Originally Posted by aeventyr60 View Post
Can you tell me about the new and Improved rear main seal?This project is looming in the next 6 weeks...need the real skinny!
I'll take a whack at this verbally, but it probably won't make a lot of sense until I get the pics & narrative posted.

The rope seal that came with the rebuild kit is white fiber around a rubber or plastic core.

The "standard" seal from Part4engines is a graphite impregnated rope seal:

http://www.parts4engines.com/index.p...roducts_id=461

The "improved" or "upgraded" seal is braided PTFE.

http://www.parts4engines.com/index.p...roducts_id=592


I'm not sure that it will make any really significant difference -- but I'm holding out hope. I figured it probably isn't inferior to the standard seal, and figured the extra money may be a good investment.

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Originally Posted by aeventyr60 View Post
Question, when installing the rear main seal does it go in dry or do you soak it in engine oil first? The scuttlebutt has it that if dry the seal tends to glaze and then leak quicker. Any opinions on this one?
Both the workshop manual and the instructions that came with the "improved" seal advise coating the seal with graphite grease when you reinstall the housing onto the crank. Keep in mind the workshop manual was talking about the original seal, and I think that the little instructions pamphlet that came with the seal was just a cut & paste job from the workshop manual.

Soaking the standard fiber seal makes sense, but I'm not sure it would do any good for the PTFE one.


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Last edited by PorFin; 04-09-2013 at 07:34 PM.
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

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...

Anyway, five years is five years. The engine was properly winterized way back when, but I'm still concerned about firing the Perkins up for the first time. I'm gonna replace the fuel, filters, oil, batteries, etc., before attempting to start. But, I'm wondering if there's anything unique to this engine I should be aware of before attempting to crank her up?
First off, congrats on the new boat.

If the PO was as meticulous as you say, you should be in good shape.

In addition to the things you listed, if it were me I'd probably pull the injectors and have them at least pop-tested. While they are out, I'd shoot a little (just a little) ATF into the bores through the precombustion chambers to provide a little lube in case the bores have developed a little surface rust.

Check all your electrical connections, and clean them up. Don't forget to pull the 8-pin electrical harness plug apart and check inside there as well.

Once you get her running, make sure to check all your fuel fittings for signs of leaks. After five years, the rubber seals may have dried out. You may want to just replace all the rubber ones now -- the scuttlebutt is that the new ultra-low sulphur diesel will leech out the stuff that made the seals swell using the old diesel, and then you're left with loose seals.

Good luck -- keep us posted with your progress.


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Re: Perkins 4.108M DIY Rebuild -- A Narrative

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PorFin,

Where did you find the piston-to-liner clearance value for your engine? I've been over my manual twice with no luck...

Ray R
Ray,

That value isn't ringing any bells -- are you looking for the delta between bore and piston o/d? If so, I don't think they give one.


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Re: Perkins 4.108M DIY Rebuild -- A Narrative

Ultimately, yes I am--either by it being explicitly specified in the manual or by subtracting the piston diameter (which is not in the manual) from the liner ID (which is there).

I can't find it on the internet and Foley (from whom I purchased the liners and pistons) has not yet responded to my inquiry. I'll try again this morning.

I ultimately decided to buy recond. rods and 0.010 under bearings. I'll have the crankshaft ground to get the clearance I want...not what I was hoping but...
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

Ray,

I haven't yet tossed my leftover parts -- I'll measure the o/d of the old pistons and put that in a post this evening. The new pistons (MaxiForce) were the same o/d as the old ones.


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Re: Perkins 4.108M DIY Rebuild -- A Narrative

I'm really surprised that the piston/cylinder clearance is not spec'd in Perky doc's. That is a critical measurement and varies significantly between cast & forged pistons. - as much as 5 thou.

I, myself, personally intend to continue being outspoken and opinionated, intolerant of all fanatics, fools and ignoramuses, deeply suspicious of all those who have "found the answer" and on my bad days, downright rude.
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

V, just curious, why wouldn't you want to turn the crank down 10 thou. for the rods? How are your mains? Are you using stock size bearings without turning them?

Why, why, why?
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

Por Fin, I appreciate that.

SloopJonB, I know, I was surprised too. They've got everything else but that.

Capnblu, I wanted to avoid turning the crankshaft because I didn't want to have to have it re-nitrided.

Crank journals are dead on. Measured the main bearing IDs, and the resultant clearances were good.

Crankpins are at the low spec limit (1.9993 inch).

My original plan was to buy new rods, install standard bearings, and then see how the clearances looked. If the clearances were acceptable to me then I would have gone with them.

But I have been unable to find anything other than "reconditioned" rods (which basically means "inspected" since they can't be re-machined), 0.010 under bearings.

So my new plan is to purchase reconditioned rods from a reputable suppler, install 0.010 undersize bearings, and then have the crank turned down by 0.010 inch nominal--the actual values to be determined by the installed rod bearing IDs.
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Re: Perkins 4.108M DIY Rebuild -- A Narrative

Ray,

I took five measurements per piston:
- Top front to back (parallel to the wrist pin)
- Top side to side (perpendicular to the wrist pin)
- Middle (between rings #3 and #4) front to back
- Middle side to side
- Bottom (across the ears)

Piston #1:
- 3.100
- 3.103
- 3.103
- 3.102
- 3.121

Piston #2:
- 3.100
- 3.103
- 3.106
- 3.106
- 3.121

Piston #3:
- 3.101
- 3.104
- 3.106
- 3.106
- 3.121

Piston #4:
- 3.100
- 3.104
- 3.105
- 3.105
- 3.121

A couple of things of note:
- The only piston that I cleaned the carbon off of was #1. That could account for the differences in the middle measurements.
- I'm now curious about the precise measurements of my new pistons (a little late in the game for that, huh?)


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