504 water pump not flowing coolant

H

harditk

Member
Tadpole
Joined
Jun 21, 2020
Messages
47
Location
Singapore
I have 2 brand new water pump installed on my newly rebuilt XN1 engine. The first one is 1202.61 and second one is 1202.71.
Both not flowing coolant. What could be the problem?
My mechanic already removed top hose and bottom hose of radiator and turning the pump but seems its not flowing water.

Screenshot_20211207-124054_WhatsApp.jpg
 
^ I second that. It's common....I've done a few. You may have not even realized that there was supposed to be one there.

Can't see it being anything else except a thermostat stuck closed. ...but I guess your mechanic discounted it being that.

It's possible to do the job without removing the cylinder head, by holding a welsh plug in there with self-tapping screws, but they have to be stainless steel as it is REALLY hard metal. Ordinary self-tappers will break. Also, you have to be careful of their placement. And the drill bit you drill the holes with needs to be thicker than if you were putting self-tappers through sheet metal, otherwise you won't get the screws to go in.

At least one hole has to be made in the cast aluminium column (which is part of the head) that the head bolt goes through.
 
Last edited:
As above, welsh plug falls out very common, very easy to fix, make sure is clean before putting new plug in, if you do use screws becareful use small ones as when putting back together impeller won't turn and can get stuck.
Cheers BP
 
BIGRR said:
Has the plug in the head pump chamber fallen out? It happens because the aluminium corrodes away. Could be your problem?

Photo shows a fix.
53054-6b40f5150692f321317fe34f319b5c98.jpg
Click to expand...
Thanks everyone for the reply. I just want to confirm. Is this the plug you are all referencing?

1638889845671.png
 
BP505v6Turbo said:
, if you do use screws be careful use small ones as when putting back together impeller won't turn and can get stuck.
Click to expand...

Heck yeah.
Try to pump in place, with gasket, to check for clearance and if it turns freely.

505s came out after 1983 or 4 without that welsh plug. That is to say, that section was blanked off, seemingly during casting of the head.
 
Be careful if using screws to secure. Experience with friends 504, the screws used were too long and were bearing on one of the head studs! Otherwise the screws {stainless} are good.
I don't think the core plug has to be a complete seal if you are concerned.
Another retaining method was an industrial sealant, [the brand eludes me for now] Selleys do a strong waterproof type also.
 
Beano said:
Heck yeah.
Try to pump in place, with gasket, to check for clearance and if it turns freely.

505s came out after 1983 or 4 without that welsh plug. That is to say, that section was blanked off, seemingly during casting of the head.
Click to expand...
Yes,
Once screws are in if new Welch plug hit in centre with a (brass block or blunt chisel) and it will spread making it a better fitment and won't fall out again, (Should be able to do it without screws)obviously dome shape facing you so it can be hit in
Has to be fairly sealed otherwise defeats it purpose.

I've learnt all this off my dad who did his apprenticeship on 504,604,505,

Hope this helps

Cheers BP
 
Waiting to hear from [I]harditk[/I] if the plug is in place or not. (And it certainly is very important that it is)

My guess is that it is.

Now, we must consider what that plug is there for - that is to direct coolant coming from the pump down through the passage in the head and through the long hole in the head gasket to the bottom of the block where it circulates and eventually rises up through the head, out and then past the thermostat to the radiator.

BUT - having looked at pictures of the head gasket and relying on memory, then if the head gasket is back to front and upside down, which I am pretty sure is possible, then the passage downwards is closed off.
Result - coolant from the pump literally has nowhere to go. A carefully bent length of wire poked down the passage way will soon indicate if there is a hole in the head gasket or not. If there isn't then its head off and reinstall with gasket the right way around.

cheers
Roland
 
Excellent, Roland !

I had forgotten about that.....and I am so used to it being the welsh plug problem that I neglected to see Harditk said it is a newly-built engine. :eek:

Some brands of gasket have the French word "dessus" stamped on one side, which means "top".....and we don't know if the mechanic knew this. Though if he was careful he should have looked to see if all the holes matched up.
 
Last edited:
Beano said:
Excellent, Roland !

I had forgotten about that.....and I am so used to it being the welsh plug problem that I neglected to see Harditk said it is a newly-built engine. :eek:

Some brands of gasket have the French word "dessus" stamped on one side, which means "top".....and we don't know if the mechanic knew this. Though if he was careful he should have looked to see if all the holes matched up.
Click to expand...
Ohh didn't see that either. Interesting the result
 
Hi all apologies for late reply. I just be able to access this site again. There was long story.
I bought a plug, but seems the head has different way to plug it (casted instead of pressed). It was rusty.
Cost to machine to make the new $5 plug fitted is too much ($300 here)
Took different route while reading performance mods thread from ThanosK. Source new head. I get 4 ports head from late model 505. The plug is casted too. China made bought from alibaba.
Coolant is flowing as per expected since.
The performance mod result can be another story.... 🙂
20230205_090801.jpg
 
Last edited:
You must log in or register to reply here.
Top