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Exhaust Reversion as an Engine Threat. #4450908
07/05/17 11:30 PM
07/05/17 11:30 PM
Joined: Oct 2012
Posts: 4,825
Taiwan
Ducked Offline OP
Ducked  Offline OP

Joined: Oct 2012
Posts: 4,825
Taiwan
Originally Posted By: skyactiv
And if the compression is on the lower side, the cat may be slowly falling apart and pieces of it getting sucked into the engine via reversion, scratching the bores up.


Thought this might be worth its own thread, since its slightly OT in the original.

I wonder how likely this is.

Car in the OP is a Nissan Altima. Dunno what model but 2.5L engine was mentioned. This might be a picture of the upper exhaust manifold and catalyst (the squid-head thing).

http://i.ebayimg.com/images/i/131110816600-0-1/s-l1000.jpg

I assume this is a potential issue when both valves are open.

The manifold seems to be for a four stroke engine, so IF say both valves are open for 10% of the downstroke, it could potentially suck-back about 60 cc's. Though the catalyst is fairly close to the exhaust ports, the intervening volume looks to be more than that. If a failing catalyst was likely to wreck an engine that'd be a fairly widespread concern and I'd have expected to have heard of it, but I might have missed it.

I don't have a catalyst but have re-invented the potential problem due to my practice of making oversized aluminium exhaust gaskets and allowing the exhaust gases to "burn them to size". The melted aluminium in the exhaust is probably a good thing, but in the cylinder, not so much.

I also sometimes put cement and aluminium in the downpipe, but that's further away from the exhaust ports and so probably less of a threat.


Last edited by Ducked; 07/05/17 11:35 PM.
Re: Exhaust Reversion as an Engine Threat. [Re: Ducked] #4450946
07/06/17 02:31 AM
07/06/17 02:31 AM
Joined: Oct 2005
Posts: 11,549
PA
d00df00d Offline
d00df00d  Offline

Joined: Oct 2005
Posts: 11,549
PA
I've definitely heard about this happening on Nissan 4-cylinders with cats so close to the exhaust ports. Altima and Sentra IIRC. This was years ago.


2008 BMW M3 Sedan 6MT
Re: Exhaust Reversion as an Engine Threat. [Re: Ducked] #4450949
07/06/17 03:14 AM
07/06/17 03:14 AM
Joined: Jul 2003
Posts: 5,074
New Zealand
Silk Offline
Silk  Offline

Joined: Jul 2003
Posts: 5,074
New Zealand
Back in the mid '70's we had a 6 cyl Thames Trader (English Ford) in, it had broken the bottom off an exhaust valve guide. When we pulled the head the piece of guide had visited every cyl. No damage done, new guides and it was good to go.


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Re: Exhaust Reversion as an Engine Threat. [Re: Ducked] #4450982
07/06/17 05:44 AM
07/06/17 05:44 AM
Joined: May 2005
Posts: 10,993
ROCHESTER, NY
Char Baby Offline
Char Baby  Offline

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Posts: 10,993
ROCHESTER, NY
The issue was with 2002-2006 Altima 2.5L.
I had an '04 without any issues however, I know others who did!


"Retired"
-----------------------------------

'80 Firebird FORMULA V8/4bbl-purchased "NEW"
'15 Nissan Altima 2.5 SV
'15 Honda Civic LX
Re: Exhaust Reversion as an Engine Threat. [Re: Ducked] #4450997
07/06/17 06:43 AM
07/06/17 06:43 AM
Joined: Feb 2011
Posts: 1,302
Golden Meadow, LA
mobilaltima Offline
mobilaltima  Offline

Joined: Feb 2011
Posts: 1,302
Golden Meadow, LA
I had an '02 Altima 2.5 with this problem. I fixed it before it had a chance to happen by installing a header with no cat. Ran great and sold it 12k miles later


2006 2500 Dodge 5.9 Cummins Mobil Delvac 15W40, Fleetguard Stratapore 90k miles
Early '99 F250 ECLB 7.3 Stroker, 223k miles
Re: Exhaust Reversion as an Engine Threat. [Re: Ducked] #4451021
07/06/17 07:25 AM
07/06/17 07:25 AM
Joined: Jan 2008
Posts: 4,113
Guilford, CT
exranger06 Offline
exranger06  Offline

Joined: Jan 2008
Posts: 4,113
Guilford, CT
It affected Sentras with the 2.5 too. I used to work with a guy who had a Sentra with this problem. Very common issue for those engines. Nissan issued a TSB for it.


2006 Ford Ranger Sport
1992 Honda Accord EX
2013 Toyota Sienna XLE AWD
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Re: Exhaust Reversion as an Engine Threat. [Re: Ducked] #4451059
07/06/17 08:07 AM
07/06/17 08:07 AM
Joined: Oct 2012
Posts: 4,825
Taiwan
Ducked Offline OP
Ducked  Offline OP

Joined: Oct 2012
Posts: 4,825
Taiwan
OK, I'd better not do that self-forming gasket thing again then, since its probably a comparable distance from the exhaust ports.

Can't work out if its likely to be a problem with my engine, but can't see an obvious reason why not.

Re: Exhaust Reversion as an Engine Threat. [Re: Ducked] #4451190
07/06/17 11:17 AM
07/06/17 11:17 AM
Joined: May 2009
Posts: 12,457
N.H, U.S.A.
ARCOgraphite Offline
ARCOgraphite  Offline

Joined: May 2009
Posts: 12,457
N.H, U.S.A.
Lead Engineer at work has an oil burning accord - looks to be same problem as Nissan - with scored bores - though they dance around it in the tsb.
Yes there is a TSB for popular honda engines failing. Imagine that. Now get over it smile


2019 VW Jetta S,6M OCI#0 1136mi-Castrol Edge Prof? VW508+OE Filter; '17 Subaru Crosstrek CVT OC#6 43467mi-Valvoline Adv 0w20 + SOA Filter
Re: Exhaust Reversion as an Engine Threat. [Re: ARCOgraphite] #4451643
07/06/17 07:06 PM
07/06/17 07:06 PM
Joined: Oct 2012
Posts: 4,825
Taiwan
Ducked Offline OP
Ducked  Offline OP

Joined: Oct 2012
Posts: 4,825
Taiwan
Any educated guesses/thumb rules as to what would be a safe distance (or perhaps volume, relative to the cylinder volume) from the exhaust ports to avoid this kind of sick-swallowing?

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