Replacing head gasket and head on a 504 - a few questions
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Thread: Replacing head gasket and head on a 504 - a few questions

  1. #1
    Fellow Frogger! Pug72's Avatar
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    Default Replacing head gasket and head on a 504 - a few questions

    Hi all

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    It's about time I pull the head off my 504. Is been leaking coolant from the rear welsh plugs for long enough. The radiator has a weep and the water pump has started to leak as well. Plus i've just notice that the master cylinder is weeping brake fluid....arrgh!

    So it's time to get stuck into it.

    Just a few quick questions -

    My only concern with removing the head is disturbing the liners ans seals. Is there a trick way to removing the head without disturbing the liner seals? I have the genuine plates to bolt down onto the block once the head is removed to stop the liners from moving upwards. So I will put these on as soon as the head to removed.

    I will be using a series 1 505 square port head. So the only issues I can see will be rerouting the heater hoses and working out the best position for the coolant hoses to/from heater and to/from inlet manifold and carby base.

    As for parts, I have a full gasket set, 505 square port head and matching inlet manifold and water pump, plus ignition leads, new spark plugs and extenders (early 505 type).

    Big questions - does the head gasket need sealant (Holymer?) and whats the best torque setting for the head bolts?

    Thank you

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    I personally would replace the liner base seals and inspect rings and bearings at this stage in your cars life.

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    1000+ Posts schlitzaugen's Avatar
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    I don't know anything about your engine, but welch plugs can be replaced in situ so to speak (you might want to get the engine out for more room to work).

    The Renault technique to avoid disturbing liner seat seals is to pivot the head horizontally to break the head gasket seal. There is a protruding dowel around one of the head bolts for this. Does your car have a similar pivot point? Manuals should tell.
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    1000+ Posts Peter C's Avatar
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    Many people (including me) don't always replace those rear welsh plugs when the engine is out. As anyone who has ever looked at a 504 engine has realised, you cannot change them in situ.

    I think the later square port heads don't have a removable welsh plug behind the water pump (?) but the ones that do were often forgotten.

    I usually use Hylomar with head gaskets unless the head surface is excellent.

    Maybe I have been lucky but I've never had the liner seals move when removing the head.

  5. #5
    Fellow Frogger! Rally's Avatar
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    Quote Originally Posted by Pug72 View Post
    Hi all


    My only concern with removing the head is disturbing the liners ans seals. Is there a trick way to removing the head without disturbing the liner seals? I have the genuine plates to bolt down onto the block once the head is removed to stop the liners from moving upwards. So I will put these on as soon as the head to removed.

    I will be using a series 1 505 square port head. So the only issues I can see will be rerouting the heater hoses and working out the best position for the coolant hoses to/from heater and to/from inlet manifold and carby base.

    As for parts, I have a full gasket set, 505 square port head and matching inlet manifold and water pump, plus ignition leads, new spark plugs and extenders (early 505 type).

    Big questions - does the head gasket need sealant (Holymer?) and whats the best torque setting for the head bolts?

    Thank you
    The liner do not usually break the seal when removing the head , clanp the liners before turning the motor over.
    The modern head gaskets do not require any sealer , they are coated with a sealer from the factory , dont unwrap the gasket before you are ready to use it and dont touch the face with dirty fingers.

    The head needs to be torqued to much higher torque then the manual says , I have done hundreds of these and use 90 ft lbs, never broken a bolt or striped a thread.
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    1000+ Posts Beano's Avatar
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    You shouldn't have to turn over the engine whilst doing the head. And in fact avoid it like the plague. There is no reason you should need to though. You should be OK if you don't. Liners are usually held in slightly by the inevitable small bit of corrosion which occurs no matter how well you have maintained your cooling system.

    Many people agree that the standard 65 ft/lbs is too low and that 70 is better. I regularly did em up to 70, 75 or even in rare cases, 80, but I think 90 is way too much unless you have a very good reason (like you're rallying ).
    I once did one up to 90 ft/lbs because the head had been skimmed and was too thin....therefore I used 2 head gaskets (a really old guy told me to). Swinging on the end of that torque wrench to get it up to 90 in one smooth last motion was difficult.

    The rear bolt hole on the drivers side is notorious for developing a stripped thread due to degradation from heat (it is on the exhaust side and at the back which gets cooled less). I have had to helicoil three of these. You can't always see it clearly on examination but specifically look for bits out of the thread.. It will not look like previously stripped threads as it will only strip when you do up the bolt this time, due to the pieces missing out of it. Look with a torch and magnifying glass, all the way down the thread. If in doubt, get a mobile helicoil guy out there. Seriously....it will save you having to strip it all down and do it again, as I had to do the first time.

    Oh....and on the subject of these threads, clean them out very well and lubricate them slightly before refitting. There has been debate here about the relative merits of a "chaser" ( an old bolt with slots cut into it) and a tap to clean out the threads. A tap can be a bit brutal on threads.
    Repco did a study once about how much more clamping force you can get with well-cleaned threads compared to not clean. It's quite substantial.

    Robmac always used Hylomar and I agree....I do too. Some brands of gasket (even Meillor) skimp on the sealant. A thin layer of Hylomar can't hurt and is good insurance.

    Andrew, I reckon you should ask Lewin about these things....that particular bolt hole and what torque he recommends. And the Hylomar.

    And perhaps also what Ianrobbo recommends. That is also what I myself would do. And you can do the rings / big ends with the engine still in place ! In fact it is easy. But I don't know how many Ks you've done, or what previous work has been done.

    Does your new head have a Welsh plug behind the water pump ? Early 505s did, but sometime in 1984 they changed (thankfully ).
    Last edited by Beano; 5th February 2019 at 07:47 PM.
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    Thanks everyone for your informative replies. I am starting to get more confident about doing this job.

    Beano - I am pretty sure there is a welsh plug sitting behind the water pump on the replacement head that I have sitting at home. See picture

    I had a chat to Lewin a few months ago when I picked up a few parts. I do need to get and see him to buy a thermostat and radiator fan switch. I'll replace these while the head is off and radiator is out getting repaired.

    I do have a new water temp gauge sender to install as well.
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    1000+ Posts Beano's Avatar
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    Yep....and luckily it looks to be in very good condition. The later ones have a recess but it is part of the cast.
    I'd be slightly inclined to peen it in various places just to be safe, but then that would disturb the seal and fit of the thing. Probably best to just let it be.
    Though having said that, I wonder if anyone ever cleans it up with a dremel and applies a bit of something like Devcon to the join ? Like a micro-repair ?

    So how many Ks has this engine done ? And has it ever had new rings or big ends ?
    Last edited by Beano; 5th February 2019 at 07:52 PM.

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    Demannu-facturing! Demannu's Avatar
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    Years ago I had my cylinder head guy weld in an aluminium disc instead of the welch plug behind the water pump. I didn't want it coming out!
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    The car has 108,000 miles on the speedo. Liner seals were done in the early 90ís. it never burns oil. So Iím happy about the rings. The motor is also super quiet, with no signs of big end bearing knock.

  11. #11
    1000+ Posts Beano's Avatar
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    Pretty low Ks ! I've seen it at a Bastille day and it's one of the most original and well cared-for 504s I have seen.

    Being a '72 model though, it will have a single circuit master cylinder so I'm glad you're replacing that. When they fail you lose ALL braking ! I have sometimes wondered about the feasibility of converting one of them to twin circuit, without having to replace the brake lines or wheel cylinders. You'd have to have the connector block (which sits under the engine bay) machined specially to have both convex flare and concave flare both in the same block. It could be done....All you'd then need would be a twin circuit master cylinder and the top sections of brake lines.

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