Topic: 400F oil leak and seal fitting

[bikeboy]

Hi guys. I've recently rebuilt my '74 400F, and have a fairly serious oil leak that seemed to come from between the head and barrels, front left. I pulled the head thinking it may have something to do with the 2 rubber seals around the dowel pins. Maybe they were pinched or something? Anyway, got my new gasket set in anticipation, and discovered the 2 seals were in place, and didn't seem to be damaged. I did notice that they weren't a tight fit in the barrel, with about 1mm gap all round. Hmm. I replaced them with the new seals, and the gap was still there?



Is this normal? Was this the source of my leak?? Do I fill the 'gap' with threebond?

thanks
ian

[MoMo]

you do have the knock pins?

[bikeboy]

you do have the knock pins?

Do you mean the dowel pins? Yeah, they were both installed. Just didn't have it in for the pic. Gap is still there with the pins in 

[bjbuchanan]

It could be the pucks under the cam tower or ANY of the o-rings under that head. Once one of them lets go it can be a challenge to try to read the gasket and head for the source

Only two of those tall rubber seals pass oil through them

My money is on the pucks, use non hardening sealant on the side to bottom edge and pop them in place. Proper sized dry o-rings everywhere else and you should be good

[Tim2005]

What make gasket kit did you use? In some kits the seals around the oil jet in the bottom of the photo are very poor indeed. The seals around the stud/dowels usually look a bit meatier than yours too.

by the way, the 400 doesn't have cam tower pucks  so you can stop wondering about those.

[Bodi]

That leak is endemic to 400-4 engines, it's from the oil feed to the head. Full pressure oil is under the head with the pressure/flow reduced by the "oil orifice valve" units. The seals around them are supposed to crush and compress on assembly, sealing the high pressure side. They usually don't seal so well. It's only about 5mm from the hole in the head gasket to the outside, so any seepage dribbles out there and results in an oily dirty cylinder section.
Having the head and barrels machined flat with minimal metal removal will help. Using the OEM Honda seal might be best, I've had them leak and also Athena ones that are a different shape. Head gasket thickness is important, too thick and the seal won't be compressed enough. You can try some sort of sealant there but blocking the orifice is fatal to the cam so it's dangerous.
I have given up on really sealing the damn things. I have a slight leak on one side, and I jam a wad of paper towel in the head/barrels gap that soaks it up - needs replacing every few hundred miles. If the leak is really bad that won't quite do it, of course.

[bikeboy]

What make gasket kit did you use? In some kits the seals around the oil jet in the bottom of the photo are very poor indeed. The seals around the stud/dowels usually look a bit meatier than yours too.

by the way, the 400 doesn't have cam tower pucks  so you can stop wondering about those.

Thanks guys. I can't remember the make of gasket off-hand, but it was an ebay purchase. The head gasket is part of a big bore kit from cruzinimage.

On another note, I was re-checking the valve clearances and got to #3 exhaust when 'twang!' goes the feeler gauge, down the cam chain tunnel! I'm hoping my magnet-on-a-stick will be able to grab it tomorrow after I (again!) remove the rocker cover

[Kwality]

Oh man - good luck!