The Ogre of Valve Seat Recession
Posted: 03 Jul 2013, 11:12
During my (forensic) investigations into the pros and cons of doing a Subaru 2.5 conversion or keeping the 2.1 litre wasserboxer I uncovered the subject of rapid Valve Seat Recession (VSR) in some engines when run on LPG. This has never been an issue with the wasserboxer (65,000 LPG miles with no VSR issues up to now) but apparently afflicts certain engines, possibly including the Subarus. I’ve not been able to get a definitive answer on exactly which engines are potentially affected but the Scoobys are definitely under suspicion.
The LPG industry keeps a kind of ‘blacklist’ of engines which are known to have problems but there is only one Subaru unit on there (the 3.0 litre flat six). However, if that engine has been found to have problems, what are the chances that other Subaru units are similarly susceptible? Yeh, that’s what I thought…
A lot of people guard against the problem by fitting a ‘Flashlube’ cylinder lubricant system (which is relatively cheap) and there are a lot of LPG-converted Subaru Legacys running about happily with these systems installed as a precaution. However, there isn’t a definitive answer even here. No-one (including Flashlube themselves) will provide a cast-iron guarantee (no pun intended – Subarus have alloy engines…
) that the problem will be eliminated by the lube kit. Actually, it can’t be eliminated as all engines suffer from it to some degree, it’s only the rate that is at issue and no-one will say how much the rate of VSR will be reduced.
I’m also unsure whether the problem is caused by the LPG being a ‘dry’ fuel (ie no lubrication properties), a hotter fuel, or a cleaner fuel (no soot), I only know that some engines can cope fine and some can’t.
A friend of mine ran a Mitsubishi L300 van for 140,000 miles on LPG, with no Flashlube, and had no problems, so some engines (including the VW flat fours) are obviously made of materials which are suitably resistant but there have been cases where recent model Vauxhalls (for instance) have suffered serious VSR in as little as 12,000 miles when run on LPG!
Needless to say, I don’t want to spend upwards of £3k and then find that my (already secondhand remember) Subaru engine suffers in this way, especially when, for a lot less money, I could have a reconditioned wasserboxer purring away in the back and be sure it won’t be an issue. Yes, the extra power of the Scooby would be great (EJ25 – 154bhp, lovely…) but a rebuilt DJ wasserboxer with fully sorted induction system and giving the full 112bhp is probably quite adequate (and certainly more powerful than the tired lump that’s in there at present).
Has anyone any direct experience or opinions to share?
The LPG industry keeps a kind of ‘blacklist’ of engines which are known to have problems but there is only one Subaru unit on there (the 3.0 litre flat six). However, if that engine has been found to have problems, what are the chances that other Subaru units are similarly susceptible? Yeh, that’s what I thought…
A lot of people guard against the problem by fitting a ‘Flashlube’ cylinder lubricant system (which is relatively cheap) and there are a lot of LPG-converted Subaru Legacys running about happily with these systems installed as a precaution. However, there isn’t a definitive answer even here. No-one (including Flashlube themselves) will provide a cast-iron guarantee (no pun intended – Subarus have alloy engines…
) that the problem will be eliminated by the lube kit. Actually, it can’t be eliminated as all engines suffer from it to some degree, it’s only the rate that is at issue and no-one will say how much the rate of VSR will be reduced.I’m also unsure whether the problem is caused by the LPG being a ‘dry’ fuel (ie no lubrication properties), a hotter fuel, or a cleaner fuel (no soot), I only know that some engines can cope fine and some can’t.
A friend of mine ran a Mitsubishi L300 van for 140,000 miles on LPG, with no Flashlube, and had no problems, so some engines (including the VW flat fours) are obviously made of materials which are suitably resistant but there have been cases where recent model Vauxhalls (for instance) have suffered serious VSR in as little as 12,000 miles when run on LPG!
Needless to say, I don’t want to spend upwards of £3k and then find that my (already secondhand remember) Subaru engine suffers in this way, especially when, for a lot less money, I could have a reconditioned wasserboxer purring away in the back and be sure it won’t be an issue. Yes, the extra power of the Scooby would be great (EJ25 – 154bhp, lovely…) but a rebuilt DJ wasserboxer with fully sorted induction system and giving the full 112bhp is probably quite adequate (and certainly more powerful than the tired lump that’s in there at present).
Has anyone any direct experience or opinions to share?