Hi everyone,
I have a Jaguar Mark 7 and I'm thinking of a LPG conversion. I have found Front end kits that maybe suitable http://www.v8dualfuel.com/lpg_front_end_kits.html for the SUs, but wanting some feedback on converting an old XK engine to LPG.
Thanks

 

I am from the mk2 forum. I am sure this might also be of interest to some of us. Cant get the link to work. But can enter manually. I have read several articles on jags with lpg fitted in the JEC mag, all seem favourable. barry

 

Thanks Barry. Any idea which edition of the JEC mag? Anyway, I'll start googling. Just wanting to find out whether an overhaul of the motor is needed before running lpg through it, or whether 'plug & play' will work. It appears that the manifolds I noted earlier are right for the job. Will leave one petrol tank and convert the other to a flat round gas cylinder [like they use in the spare wheel 'pit']. I think it will fit nicely behind the panelling, and filling thru petrol flap.

 

Based on a bitter experience with a much more modern car, I think you either need to get the heads done with harder valve seats or put in a system like flashlube to provide the missing valve lubrication. You probably know already from researching this that LPG is a very dry fuel and for a minority of engines it greatly accelerates valve seat wear. The older the car the more likely the issue is to occur as they haven't benefited from improvements in materials over the decades. If you engine has had work done for leaded vs unleaded you may already be in a good place.

Another thing to make sure of is that your cooling system is in good nick. An LPG system creates slightly more heat for the system to deal with. If your system is marginal it may start to struggle in hot weather.

If the LPG shops down there aren't very helpful try talking with John at AGAutogas in Lilydale VIC. The are a very capable crew and do LPG conversions on a wide variety of vehicles not just commercial fleet conversions. Good luck with your project.

 

I don't know how relevant this is but I ran a 1966 (186 red motor) in stock condition from 1990 until 1997 on LPG. It ran 120km day,6 days a week for 7 years. 302,000 miles and no problems at all. Only thing I did to the motor in that time was 1 rocker cover gasket and a rear main seal. It was not not set up for pulp (premium un leaded petrol) as leaded was still available then.

 

Thanks Steve. You have raised that 'other' concern - leaded vs unleaded and the older motor. The front end kits were designed for SUs on 'modern' cars. Looks like my way forward is to have the motor upgraded for unleaded fuel and overhaul the cooling system [always a good bet anyway]. Once that is paid for, then go back and revisit the pros and cons of LPG. I'll take the motor out and then I'll have the opportunity to clean up the engine bay at the same time. LPG on the back burner [excuse the pun] for now. Thanks

 

Sounds like the next few months are accounted for then

 

I had my 3.8 rebuilt by a guy that only does Jags. I asked about the valve seats and he seemed to think that this would be ok, I assume due to thier original quality. This was in regard to LPG and unleaded.
Barry

 

Thanks Barry. I have been doing a lot of reading about the hardened valve seat in the Jaguar alloy head, and as you say most regard the original in the earlier engine are good, if good. So I think a engine overall probably can't be avoided anyway. I have also read about the valve guides coming loose in the later emission hampered engines due to heat differential on the exhaust side, so considered that LPG runs hotter, the upgrading of these and the valves themselves would be beneficial as well. I have found a Jaguar experienced engineer here where I live, now I just got to find the money!!

 

Hi mk7, does your man say OK, re seats for unleaded and lpg then
barry

 

Barry, it's one of those tasks that requires the head to be removed anyway, to inspect. Some need just a regrind, while others need replacing. Hard to pin it to an exact head type though, and since later heads had hardened seats but still had failure on the valve guides, I'm not going to take the chance. I'll also need to make sure that all of the water passages are clear so a strip down would be the ultimate ( even though a good flush may suffice).

 

Another important issue is to get the timing reset for LPG. If you run 100% LPG, try and make up a hose that will enable you to fill the car from a BBQ bottle, not exactly kosher but it will save a tow.
Regards

 

Thanks for the heads-up on the timing. I'll probably run dual fuel [since it already has twin tanks - replacing one with suitable gas cylinder] and I'll be able to keep the dash a little original by using existing pump switch [modified] to activate any changeover needed.

 

For what it is worth, I have been running my 420 on LPG for about 7 years now.
The head needed hardened valve seats, and I think I retarded the ignition a bit. The car runs a little smoother on LPG, although the power is a bit down compared to running on petrol. For me that is not a big issue as I feel the 420 has enough power as is.
I have put the filler plug in the RH fuel flap, so not visible to the outside world.

 

Your comments are worth a lot. We all have our different body type but when it comes to the motor, it's very much the same. Prior to conversion, did you do an engine overhaul, or just the head? And its nice to know that the existing fuel flap can be used for the filler plug.

 

Running on LPG is fairly normal here (Netherlands). Has to do with road tax - older cars (>40 years) are exempt from tax. Normally a car on LPG pays much more road tax, up to 2 times as much. But LPG price per litre is much less - around 0,80 compared to 1,70 euro for petrol.

Anyway, I also had LPG in my Triumph 2500. That 6 cylinder wore through its valve seats very soon - I used the car a lot but had to adjust the valves every month. So I had hardened seats installed and no problems since.
In the Triumph I had a LPG injection installed, this gives more power than a common system.

When I bought my 420 7 or 8 years ago, it supposedly had an engine rebuild years before and not run much after. A few weeks after buying it, and installing LPG, due to a faulty automatic fan (not sure of the english name) the fan did not run and I had the engine overheated. After that it used a little water so I pulled the head. The head gasket was at fault.
Because the head was already off this was a good time to put in hardened valve seats.

By the way - the XK engine had much less wear on the seats than the Triumph head. Maybe the XK valve seat material is of a harder specification? Whatever, I would have done it anyhow if only for peace of mind and for less valve adjustment. Which of course on a OHC head with shims is a fair bit harder to do. I could adjust the Triumph valves within one hour, try that on a XK engine!