I was attempting to install the evo half moon seal in a 1g head and it doesnt fit by ~ half a mil. Measured head width as 8.7 +/- 0.1-0.2 mm with some wider spots. Inner width of the seal was closer to 8.4-8.5mm. When installing it, I put Threebond 1207 on the inner race of the seal and the corners. After tapping it pretty good with a wood block, it sat proud of the valve gasket surface by probably 1/8". I lightly sanded the exterior of the head a bit, and it seemed like it wanted to fit a bit better but never really fit correctly.

Have a new seal on the way since the old one got pretty marred up when removing it, maybe I just had a bad casting or something.

In case the next one has similar measurements, what would the correct path forward being to get it to fit up right? I figure the 2 options I have would be to remove material from the exterior side of the head, or remove material from the seal.

Thanks!

athlete3344 said:

I was attempting to install the evo half moon seal in a 1g head and it doesnt fit by ~ half a mil. Measured head width as 8.7 +/- 0.1-0.2 mm with some wider spots. Inner width of the seal was closer to 8.4-8.5mm. When installing it, I put Threebond 1207 on the inner race of the seal and the corners. After tapping it pretty good with a wood block, it sat proud of the valve gasket surface by probably 1/8". I lightly sanded the exterior of the head a bit, and it seemed like it wanted to fit a bit better but never really fit correctly.

Have a new seal on the way since the old one got pretty marred up when removing it, maybe I just had a bad casting or something.

In case the next one has similar measurements, what would the correct path forward being to get it to fit up right? I figure the 2 options I have would be to remove material from the exterior side of the head, or remove material from the seal.

Thanks!

Click to expand...

Is this an OEM metal half moon? They will generally sit a little proud in my experience but not 1/8". If you push it down with your thumb where does it sit?

Yup, OEM. Honestly, I could barely push it down into the groove to get it started. It took several harder taps w a block of wood and hammer to get it moving.

I would just get another or use the rubber one.

The rubber ones measure about 8.5-8.6 mm (I actually measured 8.55-8.56mm) and, obviously, will stretch a little bit if needed. I probably have a metal 4G63 half moon somewhere but I could end up looking all night for it and never find it until Saturday.

FWIW, I have a metal half moon from a 420A (part number M04667731 or just 04667731), it measures about 8.3mm, definitely doesn’t fit the 4G63 head. Could easily be mistaken for the 4G63 seal without measuring.

Whenever the new one shows up ill take some pics w/ measurements and ill see if i can find where I tossed the last one.

Ok, new one showed up and similar story. Same fitment issues - see pics. Seal sits fairly proud after pushing this thing down as far as possible. It definitely feels like its binding up. In the 3rd fitment issue pic, you can see the gap left after the seal is fully seated. Both the inside and outside of the head surface is perfectly clean, no left over RTV from previous seal.

Head thickness = 8.7-8.9mm, measured in 3 spots.
Half moon width = 8.6mm, measured in 1 spots

Head:


Half moon:


Fitment issues:

I ended up sanding down the outside of the head and used the seal as a guide. I marked the head with highlighter, ran the seal around the opening, sanded down the shiny high spots (hard to see in first pic), cleaned, repeat. Took maybe 20min using 220 grit.

Seal now drops in like it should.




I was able to really see all the high spots and get a good marked line by trying to insert the seal partially at different orientations.

What will happen now, if you were to go back to the rubber seal? Do you think it WOULD SEAL after you altered the head? Just askin.

I'd imagine it would seal correctly now, and I'm not planning on using a rubber one.