Does anyone know what the size is for the Welch plugs at the rear of the MI16 1.9 XU9J4 motor. These are the ones under or near the exhaust manifold. There are 3 cup Welch plugs and I can't work out if they are 20mm, 21mm or 22mm and I can't find any reference to size in the manual. Thanks Mark
405 MI16 Welch plug size
- Thread starter Judders
- Start date
Measure the hole size. You will need to gain access to fit anyway
Welch plugs are 0.25mm – 0.40mm (0.010″ – 0.015″) oversize which is the interference fit required when installing
Get some Welch plug sealant as well when fitting.
Match stick in a rusted leaker will get you home.
Wood swells when wet, perfect seal.
Welch plugs are 0.25mm – 0.40mm (0.010″ – 0.015″) oversize which is the interference fit required when installing
Get some Welch plug sealant as well when fitting.
Match stick in a rusted leaker will get you home.
Wood swells when wet, perfect seal.
Thanks Driven. I have the engine out of the car at present so I have full access. I measured the hole and i'm between 20mm and 22mm. I have 20mm brass Welch plugs and 22mm brass Welch plugs. Then I read that brass Welch plugs should not be inserted in an aluminium alloy head. I have ordered 22mm steel Welch plugs but while I wait for them I have my doubts and I reckon it's either 20 or 21 so I was hoping someone could give me a definitive answer. Otherwise I will just work my way through the varuos options as Welch plugs are not to expensive.
Seems like an excessive amount of interference fit to me, for a Ø22mm hole. I'd buy oem. I bought some off the shelf Ø27mm brass plugs recently for an XU10J4 and had to turn them down for a 0.004" fit.
I guess you're talking about the three in the head? There are none in the block on the exhaust side. I agree they are difficult to measure, but I'd suggest Ø20mm. I've never replaced one. Seems strange to me. Are you sure it's not the head gasket leaking?
Thanks Peter and Run205. 20mm it is.
When the car was inspected for RWC a few months ago it was reported back to me as a leaking head gasket.
I had a pressure test done at the time and that was then changed to leaking welch plug. I have pulled the motor out because I wanted to clean everything up and do some other things which would be easier with the engine out. Once I had cleaned the motor there was no evidence of any leaks at the welch plugs but I found that the water pipe at the back of the engine was badly corroded where it joined the rubber hose and that was definitely leaking. I thought that was most likely the culprit and it was possibly spraying coolant in a way that made it look like the welch plug was leaking. Then I was reading back through the service / maintenance history and I saw a note had been made back in 2010 about leaking welch plugs so I thought maybe I should just replace them while the motor is out. Now I'm starting to doubt if I should. I don't really want to disturb them if they aren't leaking. I also will kick myself if I put the motor back and the welch plugs are leaking. Hmmm, tricky?
When the car was inspected for RWC a few months ago it was reported back to me as a leaking head gasket.
I had a pressure test done at the time and that was then changed to leaking welch plug. I have pulled the motor out because I wanted to clean everything up and do some other things which would be easier with the engine out. Once I had cleaned the motor there was no evidence of any leaks at the welch plugs but I found that the water pipe at the back of the engine was badly corroded where it joined the rubber hose and that was definitely leaking. I thought that was most likely the culprit and it was possibly spraying coolant in a way that made it look like the welch plug was leaking. Then I was reading back through the service / maintenance history and I saw a note had been made back in 2010 about leaking welch plugs so I thought maybe I should just replace them while the motor is out. Now I'm starting to doubt if I should. I don't really want to disturb them if they aren't leaking. I also will kick myself if I put the motor back and the welch plugs are leaking. Hmmm, tricky?
initially got thrown a little when you said "motor" and assumed you meant the block
I haven't ever removed a leaking welch plug or the coolant pipe
if you cleaned the whole donk before inspecting its possible you removed evidence of the leak(s)
that's a shame as an inspection before removing signs of the leak is what's needed
you probably would have been able to track the leak from the bottom up to the source
does sound like you've got a leak or leaks from those plugs
the coolant pipe leak is just at the rubber hose join and should be fine with a new hose
you can get those coolant pipes for the other XU's but for some reason couldn't find a ref to it on yours
Peter is vastly experienced and may be able to point you to a procedure that works
I'd only guess at ordering the OE ones, removing the old plugs carefully, cleaning, freezing new ones and tapping in to get your intfrnce fit
I haven't ever removed a leaking welch plug or the coolant pipe
if you cleaned the whole donk before inspecting its possible you removed evidence of the leak(s)
that's a shame as an inspection before removing signs of the leak is what's needed
you probably would have been able to track the leak from the bottom up to the source
does sound like you've got a leak or leaks from those plugs
the coolant pipe leak is just at the rubber hose join and should be fine with a new hose
you can get those coolant pipes for the other XU's but for some reason couldn't find a ref to it on yours
Peter is vastly experienced and may be able to point you to a procedure that works
I'd only guess at ordering the OE ones, removing the old plugs carefully, cleaning, freezing new ones and tapping in to get your intfrnce fit
If the engine is out of the car, I’d hook up something to pressure test it. ie block off inlet and outlet and feed 10psi of air in somewhere. You’ll soon hear/see the leak. The Daytona pressure bleeder would be perfect.
Peter your suggestion worked a treat. I blocked off all inlet and outlet pipes as best I could. Connected my pressure bleeder to the bleed screw on the coolant pipe at rear of the head and pressurized it to 10psi. Then I sprayed soapy water over the Welch plugs and other points of interest. The bleed screw on top of the thermostat housing was leaking but the Welch plugs showed no signs of leaking. I did it several times and I am confident. At this point I will not be messing with any Welch plugs. Thanks all for you.
Cheers
Cheers