504 XN1 Head Gasket/Piston Liner Question
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Thread: 504 XN1 Head Gasket/Piston Liner Question

  1. #1
    BGJ
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    Default 504 XN1 Head Gasket/Piston Liner Question

    Hi all:

    Apologies for starting another thread on this topic, but I just couldn't find the right answers in any of the old/existent threads.

    I've removed the engine from my '79 504 sedan in order to get the gearbox off—that's now at a mechanic with some new bearings and will hopefully come back without that high-pitched wine in all gears but 4th.

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    While I have the engine out, I decided that I might as well change the head gasket: further inspection revealed a very small amount of oily/sticky gunk around the water-pump hose connections and a small amount of emulsified/white oil in the breather, suggesting that a new gasket is necessary, not optional.

    So, I have the head off now, and I come to my question: The Haynes manual gives instructions for replacing the gasket only and suggests the piston liners shouldn't be disturbed unless by a professional workshop (seemingly just to measure the protrusion properly). But every thread I can find on this forum assumes that the lower liner seals get replaced as part of the gasket replacement (and just use the thickest liner seal, not worrying about measuring protrusion). Is this necessarily the case? I have some spare bolts to use as the 'liner clamps' but haven't actually used them yet—the liners are currently tight/not moving at all, and it seems disingenuous to tighten them directly (surely that's only going to disturb them, especially if done the way the manual shows, clamping only one side of each liner?).

    If the answer is yes, I must replace the lower liner seals, do I then basically have to remove the whole crankshaft and pistons in order to remove the liners?


    Many thanks!

    Ben

  2. #2
    1000+ Posts Peter Chisholm's Avatar
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    While you're at it, check the condition of the welsh plug behind the water pump impeller. Also, replace the two welsh plugs at the back of the head as they rust from the inside out and this may not be apparent.

    Not sure about the oily gunk around the hoses but a white, oily deposit inside the breather is often just condensation and therefore not necessarily a sign of a leaking head gasket.

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    BGJ
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    Ah, interesting on the oil breather. I also thought that the gunk in the coolant tubes was so minimal that it could have been from grease used to slide the hoses onto the pump (I can't actually remember using grease for this, but I can imagine myself resorting to it without thinking about the effect on the hose rubber). Doesn't matter... I'm committed now!

    On the welsh plugs: yes, I was thinking about this. Your response might be the push I needed to order replacements and just do it.

    Cheers,

    b

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    1000+ Posts Beano's Avatar
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    Quote Originally Posted by Peter Chisholm View Post
    While you're at it, check the condition of the welsh plug behind the water pump impeller. Also, replace the two welsh plugs at the back of the head as they rust from the inside out and this may not be apparent.
    I second this.

    Quote Originally Posted by BGJ View Post

    If the answer is yes, I must replace the lower liner seals, do I then basically have to remove the whole crankshaft and pistons in order to remove the liners?
    You don't HAVE to replace the liner seals, but if you want to do it, you do not have to remove the crankshaft.

    I'd recommend just making sure the liners have not moved at all, and just do the head.

    Some people don't trust the liner seals though, so if you want to do em, leave the crank and timing cover in place, but remove sump and oil pump, mark conrods and end caps with a file, and push pistons out top of engine.

    With engine upright, get two large levers and work the liners back and forth till they come loose from the scale which has cemented them in, and pull up. Have patience...it takes a little while (though not long), but there is an outer lip around each liner, and lever them up via this.

    Mark the liners with a file too.

    Don't remove the distributor completely (remove cap and rotor so they do not get broken).

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    BGJ
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    Thanks for this, Beano.

    To be honest, this is what I wanted to hear. I just wasn't sure if, in practice, anyone actually trusts those liner seals after removing the head.

    I'll get some welsh plugs on the way and work on finding something to help dissolve some of the old gasket and go from there...

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    It's the same old problem with all wet sleeve engines. Renaults are worse but Peugeots are also prone.
    I had a 505 with leaking sleeve seals, my first 505, and I just threw in another engine.
    Although you may be able to do the job without completely dismantling the engine I would suggest that tinkering around the edges and doing half a job will get half the results you are looking for.
    Mechanics have taught me that cutting corners almost always leads to tears and having to do the job again or abandon the project.
    The proper way is to completely strip the block, have it chemically cleaned and have everything measured for wear and fit new stuff as required.
    No short cuts if you want joy afterwards.
    Sorry, the laws of physics don't change for anyone.

    PS,
    Otherwise leave well alone and shove it back in and hope for the best, expecting the worst.
    I doubt you'll be surprised in the longrun and most likely it will $hit itself at the most inconvenient time.
    Don't ask me how I know this.
    Last edited by luthier; 21st October 2016 at 11:09 PM.
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    1000+ Posts Beano's Avatar
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    In theory I agree with Luthier, but in reality I have done both. And actually, the more I think about it, the more I agree with Luthier.

    Waggle the liners with your fingers. If they move, you're screwed and MUST replace the base seals.

    Otherwise, it's up to you which way you go. My personal choice would be to do the liner seals....it's not a complex job and is basically like a Meccano set. The job is labour intensive but not knowledge intensive.

    Just mark everything (have you done this sort of stuff before ??? ). Mark the front of each piston (down on the bottom on the inside) with a scratch. One scratch for piston # 1, two for # 2, etc...
    Same for conrod caps. And liners.



    504s only run a 3 pound radiator cap, which is pretty damn low. That is all the cooling system is rated to. If you decide to NOT do the seals, and get water in the oil at a later date, Chemiweld will seal it up, no prob. Don't assume it is the head gasket again....it will be a liner seal.

    To remove old head gasket remains, use a scraper, and buy a small bottle of nail polish remover from Coles at a massive $ 3.50. It contains acetone. Maybe use it with a green scourer.

    Don't even think about using sandpaper, unless it's really fine ( more than 600 grit), and you vacuum out the bores later. Or have rags stuffed in them.
    Last edited by Beano; 22nd October 2016 at 01:56 PM.

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    Okay, okay! The collective weight of your advice to do it properly is becoming persuasive.

    I'll give it a go next time I have a full day to spare (the gearbox won't be done for a while anyway, so I'll take my time).

    Thanks.

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    1000+ Posts Beano's Avatar
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    I don't usually completely strip the block.


    When you replace the oil pump/strainer, you will need a new O-ring (easy to get).

    When you remove/replace the pistons together with the liners, you can only do two at a time....the crankshaft counterweights for the other two get in the way. Rotate crank 180 degrees to do the other two.
    As always, taking apart is easy. Putting together needs attention to detail.

    I usually clean the block where the liners seal at the bottom with a largish wire wheel on an electric drill. Then I do the same with the liner bases and the scale/mineral buildup on the outside of the liners.

    Get a couple of blocks of wood about the size of bricks (but a bit longer) which you can sit the block on upright, when you need to.

    When you tighten up the oil line to the tappets, do not overtighten....the bolts are hollow and break easily. Gentle is better and the washers are copper anyway.

    Before replacing the head, clean out the head bolt holes in the block very well, and take a long hard look at the rear one on the exhaust side.....it gets hottest and often needs a helicoil.

    I can't emphasize this enough. Many people have come to grief here. They tighten down the head and this bolt won't torque up completely....then the gasket leaks and everything has to come off again

    Any bits missing off the thread or anything that doesn't look perfect will put it into this category. I've had to do a few of these, and 504s are not getting any younger. If you've never helicoiled, best to get someone else to do it.....a single one is not expensive, especially if you take the block in to them.

    Lubricate those holes (and bolt threads) with a tiny bit of grease before finally screwing in bolts.

    Oh...and use spray-on Hylomar on the head gasket....our most senior / experienced member (Robmac) also recommends this. The sealant head gaskets already have on them is pretty sparingly applied.

    One last thing : the rocker gear has to go on WITH the head, as the head bolts go through it. The whole lot is rather heavy, so best to have another person help you place it on the block. It's not ABSOLUTELY necessary, but you don't want to scuff up the spray-on Hylomar on the head gasket, as you're plonking the head/rocker gear on there.
    Last edited by Beano; 22nd October 2016 at 10:24 PM.

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    BGJ
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    Thanks for all this Beano. It looks like useful advice. Is the oil pump seal a standard size (i.e, likely available from a local non-specialist)?

    I spent a couple of hrs today just slowly working off the old gasket remnants. Will keep you updated when it's all done.

    b

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    When reassembling head on to block it is worth giving thought to having a couple of threaded inserts that can be used to keep head,gasket and block in line.

    There are a variety of solutions to this issue, the neatest of which is short studs with the correct thread which have been drilled and milled to allow removal with a t-bar after the head has been seated, then to be replaced with the normal studs

    Andrew

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    1000+ Posts Beano's Avatar
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    As far as I remember, the oil pump seal is a standard size.

    I forgot to mention that a brass wire wheel and drill is my favourite method of taking off old gasket. Though you can buy those Scotch Brite pads for electric drills these days, I believe. Somewhere.

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    Thanks, Andrew. I'd considered getting new head bolts and using the old ones in a similar way as guides.

    Beano: I had a wire-wheel setup but was a bit worried it would be too aggressive on the alloy head. All done now, so I guess it doesn't matter. The reason I asked about the seal is that I've already completed orders from Franzose and Serie04 so will have to find the seal locally to avoid the shipping charge again. If it's just an o-ring, I'm sure I'll find it. Somewhere.

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    BGJ
    Not sure you need new head bolts for your model. Most reuse.
    I have some old head bolts, cut off, with a screw driver slot .....use as a guide and then undo.
    Can drop them off one day if you wish.
    Bob
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    1000+ Posts Beano's Avatar
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    Yes....use wire wheel on block only. It's best to not even use a rotary scotch brite pad on the alloy head. Some mechanics do, but others shudder at the practice.

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    as head guides i wouldn't use the regular head bolts, because their shank is a bit thinner than the thread. i bought long bolts for lowering the front crossmember, and they turned out to be the same thread as the head bolts, but with thicker shank, cut their heads and made slots in them and they will be my guides when i install the cylinder head.

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    Thanks 2pac and Bob D. I've had a bit of a break but will get back to it this weekend.

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