Blown head gasket for the second time...

[Faber32]

Hi everyone, I have a People GTi 125 with 25k miles on it. I have an issue at cold start, wet spark plug. Same symptom it had when at 12k miles I had a blown head gasket, leaking coolant into the chamber (repaired by a Kymco service). Now I removed the spark plug and I see red drops of coolant on the piston so it seems the same again.
I don't know how it could happen, but the scooter is driven by my brother too who I suspect has a "heavy hand" on the gas at this point.
Two days before the event I did an oil change, draining all the oil carefully inclining the scooter also to remove all the oil from the sump. I use first quality oil and coolant, HiFlo oil filter. Next days he did a couple of trips of 50 miles on state roads (around 40 miles per hour) each with a lot of heat (37-38 °C). Could this heat do this? Or is his driving style?
Or is it a known issue for this model?
I don't know what to think, and I don't know if I should repair it considering that the issue happens regularly. Thank you for help

[Ruffus]

Since you had an waterpump issue recently, I would suspect that one first.

[Faber32]

Hi, what waterpump problem?
How can I know if the waterpump works properly?
Thank you very much

[Ruffus]

Meant that one from 15 oct 2023


Good morning guys   Yesterday I replaced coolant on my People Gti 125. I made a mistake. When filling new coolant, I started the engine for some seconds (classic procedure to bleed air), revving up lightly, topping up while radiator level was going down and after shutting off the engine I opened the bleed screw near thermostat to bleed air from the circuit. After 6-7 times of this start&stop, air was still coming out from the bleed screw. It seemed strange to me so much air was still trapped, so I started the engine and let it idle for minutes to see what happened then. I was waiting for the fan to start, but it didn't. How can I know if the cooling fan is broken without a diagnosis scan tool?
Also, after 7-8 minutes the temperature went from the safe level 2, to level 3. I immediately turned off the engine.  Then it happened a second time after, evidently there were still some air bubbles inside. Or it was simply overheating because it was idling still and fan not working. At some point also the CEL appeared but I turned off immediately. Do you think I could have damaged the engine? Or the new coolant itself?
Thank you

[Faber32]

oh yes, you're right. But that time I think it was a bubble inside the circuit, I solved immediately after doing the air bleeding again. And the scooter worked properly for 2 years so I don't think it could be the cause of the blown gasket. I would have destroyed the engine I suppose and I never noticed overheating.

I decided to replace the head gasket by myself, I'll post pictures of the damaged gasket as soon as I do it

[Faber32]

The head gasket is definitely blown. Same point as the last time. I don't know, maybe a not perfect valve clearance or too hot exhaust gases. I don't know

[Ruffus]

When you get the new gasket, compare (with a magnifier if neccessary) old and new.
Pay attention to clippings for water canals, not to be to small or in the way of coolant.

[Faber32]

You say it could have been a factory defect? I destroyed two head gaskets in the same exact point.

While I had the head in my hands, I also noticed that if I push the camshaft pulley in and out with a finger it moves a lot, I'd say almost 1 millimeter. I think something is off but don't know what.

If you notice, the stud at the top right in the picture, seems off-centered with respect to the cylindrical invite. I really don't know

[Ruffus]

No, I'm not saying it could be a factory defect.
Just check upon the new gasket, whether
a) its original
b) its exact for this model
c) how does it fit on the cylinder
d) are studs exactely centered
Mounting:
- are the studs having the exact lenght above cylinder?
- use the exact torque and retorque after a few hundreth kilometers
- use NEW cylinder head nuts and washers.

[Faber32]

gasket is Kymco original.
Today I checked the head warpage and I think is off specs. In a particular direction I can fit a gauge of 0.05 mm, so it needs to be resurfaced. But now I have also doubts about the upper/right stud that seems bent. I have also doubts about having done the wrong procedure in removing the head, I removed the 4 head nuts first and then the two side screws. And for installation, do I have to do first the 4 nuts and then the side screws, right?

I also have doubts about the chain tensioner. When reinstalling it, does it have the flat screwdriver screw inside to retract the piston? Thank you

[Ruffus]

Does not make a difference which nuts first.
About tensioner piston don't know what you mean.
Tensioner goes in with flat part direction cylhead. (see pic)

[Faber32]

I'm assembling the engine again. Now I have a doubt. The "T" mark on the flywheel is horizontal with a vertical mark on the right (see pic). I suppose the mark on the right is the one to align with the reference marks. Done this, now the camshaft pulley seems a little bit off alignment. You know that there are two holes on the pulley that must align with the head surface. But I see one entirely and the other just a little. It's like 1-2 degrees off.
So I tried to remove the chain and put it one tooth in the other direction but it's way worse in the other direction.
Why I can't align the engine as in the manual? I'm afraid of starting it with this doubt. Thank you

[Faber32]

Okay. Jobe done. Engine runs as new now.
But I have a doubt. With new piston rings, should I replace the oil after about 200 miles as if it was a new engine? And then is it needed another oil change at about 600 miles?
Thank you

[Iahawk]

impressive work and nice to see it completed! If in doubt I always change the oil...small sump capacity combined with (I assume) no oil filter? Inexpensive insurance.

[Ruffus]

Yes as hawk says, there is always the chance to have a smitheren or chip of something in it., particular with new rings which are "honing" into cylinder walls.