Tensioner bore through chain cover specs

Jameel · 12-27-2021, 07:41 AM

I'm fixing an oil leak where the oil line feeds my right side tensioner. It's not leaking at the banjo fitting, but where the tensioner comes through the cover. The bore in my chain cover is not very smooth, so I don't think the o-ring is doing its job. Also, the o-ring for these seems like its not quite large enough. It's pretty much the same size as tensioner boss, so, no real squish factor. I want to clean up the bore in the cover, but don't want to make the hole too large. So that bore spec would be useful.

hcoles · 12-27-2021, 08:47 PM

When I rebuilt the top of my motor I noticed the fit was, I thought, too loose with the O ring supplied in the VR kit. I installed a slightly bigger O ring. Experts can chime in .... O rings can be "pinched" say 25-35%. Too much and they fail in compression during the install, too little and they may leak. Your picture shows a mating hole will not compress that O ring much if any.

john walker's workshop · 12-28-2021, 07:55 AM

A smear of Dirko helps. Yes, we need better o-rings.

Jameel · 12-28-2021, 08:16 AM

Quote:

Originally Posted by john walker's workshop

A smear of Dirko helps. Yes, we need better o-rings.

Thanks John.

dannobee · 12-28-2021, 09:08 AM

That o-ring is too thin. When machining stuff for o-rings, it normally calls for the o-ring to stick up 20-25% over the depth of the groove, so that there's adequate compression of the o-ring. That doesn't even look anywhere close to that. More like 5% over, if even that.

There's a Parker-Hannifin O-Ring handbook that's like the bible for everything o-ring related.

https://www.parker.com/Literature/O-Ring%20Division%20Literature/ORD%205700.pdf

boyt911sc · boyt911sc's Garage

Quote:

Originally Posted by Jameel

I'm fixing an oil leak where the oil line feeds my right side tensioner. It's not leaking at the banjo fitting, but where the tensioner comes through the cover. The bore in my chain cover is not very smooth, so I don't think the o-ring is doing its job. Also, the o-ring for these seems like its not quite large enough. It's pretty much the same size as tensioner boss, so, no real squish factor. I want to clean up the bore in the cover, but don't want to make the hole too large. So that bore spec would be useful.

Jameel,

For better sealing, use a M1200-200 (12-mm x 2.0 mm) Viton or FKM o-rings for your Carrera hydraulic tensioners. As you had noticed, the OEM o-ring is a little bit undersized. Do some measurements:

ID of the bore on the chain housing cover for the tensioner = 16 mm.
OD of the groove section where the o-ring sits = 12.5 mm.

A 12-mm x 2-mm installed on a 12.5-mm OD shaft would have a resultant OD = 16.5 mm. Just right for the 16.0 mm bore on the chain housing cover. I had done some troubleshooting in the past to correct the oil leak. It is critical that the mounting surface on the tensioner where the 8-mm banjo and crush washer sit is flat and smooth.

Tony

Jameel · 12-28-2021, 03:15 PM

Great info Tony. Thanks! I'm going to hunt down some of those rings after I measure up. Also will make sure the flat on the tensioner boss is flat.

Jameel · 12-28-2021, 03:16 PM

Quote:

Originally Posted by dannobee

That o-ring is too thin. When machining stuff for o-rings, it normally calls for the o-ring to stick up 20-25% over the depth of the groove, so that there's adequate compression of the o-ring. That doesn't even look anywhere close to that. More like 5% over, if even that.

There's a Parker-Hannifin O-Ring handbook that's like the bible for everything o-ring related.

https://www.parker.com/Literature/O-Ring%20Division%20Literature/ORD%205700.pdf

Thanks for this. That pdf is good reading.

mikedsilva · 12-28-2021, 04:20 PM

Is it of any value to use some Curil T around that o ring, when installed the timing cover?

So far I have not had one of these leak. I do agree that the o rings supplied in the WR kit look a little skinny, but for me they have worked so far. I don't think the o ring here needs that much tension- it is not under pressure such as the case through bolt o rings. Or am I mistaken?

john walker's workshop · 12-28-2021, 05:26 PM

Seen plenty of them seeping there. A simple application of sealer saves having to deal with leaks later.

Walt Fricke · 12-28-2021, 05:59 PM

There probably is very little oil pressure on those O rings. However I once had a tensioner go bad (the valve on the top of the tensioner blew off), so I replaced at the track with a non-pressure fed one, and stuck a plastic cap into the now unused hole in the chain box cover. Worked, so I got lazy and didn't do a real fix. Next event the plug blew out. Lots of oil blew out. Certainly enough pressure to cause a weep if there is an opening, however small.