Where to find help when you want to change major units on your CF - engine, transmission, brakes etc. - or upgrade earlier models to later specifications.
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Unleaded Cylinder Head Mod's Are they Needed?

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Post by jomac_uk » Subscribing Member » Thu Dec 27, 2018 5:52 pm
Joined: Tue Dec 11, 2018 7:45 pm
Posts: 7
Google can be your friend, but at time's can also be your enemy. I have an 81 CF with the 2.3 engine. The old boy who used to own it, spent silly money doing a lot of work on the engine before he passed on. The engine and it's oil is spotless, so i guess it's not old mileage wise from the rebuild. I have no way of telling if he had the seat's hardened for unleaded petrol, but a couple of guys have said, they never bothered and still run their CF's with the original heads, both after several 10,000's of miles, one owner does put additive in though.

My question here, i fully intend to add an LPG conversion to my CF, primarily because i have one, and in addition, LPG is much cheaper. Running a vehicle on LPG, would this have the same effect as running it on unleaded fuel?

Would my cheapest option here, be to assume it has had the head modified and see what happens?
I started out with absolutely nothing and still got most of it left.! ;)

Re: Unleaded Cylinder Head Mod's Are they Needed?

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Post by Phil Bradshaw » Club admin » Fri Dec 28, 2018 6:40 am
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3827
When leaded petrol was all the rage valve seats machined directly into cast iron cylinder heads lasted around 70000 mile (or less, e.g. BLMC A series).

On the Vauxhall OHC engine once exhaust valve seats have receded past 1.13 inch valve stem height above the cylinder head and no valve clearances can be obtained with 2nd under-size tappet adjuster screws the answer provided by GM was to fit a new head.

Technology has moved on some however; nowadays hard valve seat inserts can be installed in Vauxhall OHC heads (instead of dropping out using old-style location methods - head gets too hot for shrink fit etc.).

For running on LPG Flashlube or similar upper cylinder lubricant bled into the intake by a metering device is the way to replicate additives for petrol getting at the hot bits.

Hard seats for LPG once fitted should outlast original exhaust valves (GM, Tranco etc.); upper cylinder lubricant then will protect the relatively softer valve heads provided they don't overheat to the point of suffering Brinelling damage.

If the head on your CF has had hard seats fitted then the exhaust valve clearances won't need adjusting so often (which also depends on how hard the engine has to work, both physically and against any problems like overheating, wonky fuel or ignition etc...)

If the engine is running alright now then a good start would be to adjust the valve clearances and note the actual clearances obtained as well as the the mileage then check the clearances every 1000 mile or so.

What you'll be looking for is any of the exhaust valve clearances closing up; an adjuster screw turning a click or two (full turn, about 0.003" a turn) within about 6000 mile or so wouldn't be unusual in leaded petrol days, i.e. without hard seats.
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  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Unleaded Cylinder Head Mod's Are they Needed?

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Post by VDUB384 » Club admin » Sun Dec 30, 2018 11:25 am
Joined: Wed Sep 12, 2012 9:01 am
Posts: 1400
Like Phil says,If you intend to fit LPG You need to make sure you have hardened valve seats in the exhaust valves and Flashlube kit running with the engine. I used LPG on my cf350 Coachbuilt camper I used to get 17 mpg on petrol and 13/14 mpg on LPG you do however have to watch the engine temperature because it dose run a lot hotter on LPG but found constant running on LPG meant when you ran out and needed to use petrol it ran like a bag of crap.
Dave
Whilst good maintainece is the best prevention"If its not broken don't fix it."
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Re: Unleaded Cylinder Head Mod's Are they Needed?

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Post by jomac_uk » Subscribing Member » Sun Dec 30, 2018 12:12 pm
Joined: Tue Dec 11, 2018 7:45 pm
Posts: 7
Interesting comments, I did get a reply in my FaceBook group on CF Motor Homes and knowing if a head has been modified. One guy suggested using one of these endoscope camera's that you can use with a mobile phone and look for a darkened skirt around the exhaust valves.

But that aside, why would the engine run like a bag of nut's after running on LPG? I've had several Rover SD1's over the years and a Rolls Royce that were fitted with LPG conversions. I never really had any issues like this with any of them switching between the two. I wanted to fit LPG for 3 reason's, 1, i already have the kit removed from a car. 2, better economy. And 3, i can run the internal heating and cooking and hot water from the tank without having to carry a gas bottle or two around.
I started out with absolutely nothing and still got most of it left.! ;)

Re: Unleaded Cylinder Head Mod's Are they Needed?

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Post by Phil Bradshaw » Club admin » Sun Dec 30, 2018 4:12 pm
Joined: Sun Sep 02, 2012 7:15 pm
Posts: 3827
Poor engine performance on petrol after running on LPG may be due to a problem with the carburettor, or even stale petrol if enough of the light end fractions have evaporated. Also, spark plug gaps and ignition timing for best running on LPG won't be right for petrol.

I'd like to see how an endoscope would help; normally it's hard to distinguish inserts from seats machined into the head until combustion deposits are scrubbed off. Indeed, thinwall seats can be almost indistinguishable from original seats until valves are removed to examine the ports for seat lip/protrusion.

Later head (rotator caps on exhaust valves) with all seats fitted with inserts and valve guides fitted with sleeves -

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Same head with valves inserted (numbered from the back of the head here) -

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  • What is real is not the external form but the idea, the essence of things. Constantin Brâncuși

Re: Unleaded Cylinder Head Mod's Are they Needed?

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Post by jomac_uk » Subscribing Member » Sun Dec 30, 2018 11:16 pm
Joined: Tue Dec 11, 2018 7:45 pm
Posts: 7
I'm beginning to think an additive is the simple answer here.!
I started out with absolutely nothing and still got most of it left.! ;)

Re: Unleaded Cylinder Head Mod's Are they Needed?

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Post by VDUB384 » Club admin » Wed Jan 02, 2019 10:36 am
Joined: Wed Sep 12, 2012 9:01 am
Posts: 1400
Hi Jomac, You say you don’t know why the cf should run like a bag of nuts,we’ll take it from me I ran my CF350 for 8 years mainly on lpg and when I used petrol which incidentally was only when I run out of lpg it ran very badly. I had the carburettor looked at on many occasions and also had a rebuild kit put in it. And yes I’ve had VWs on lpg with no difference running on petrol, and when I said about watch for it running to hot I went through two cylinder heads that ended up cracking so I think I know what I’m talking about. As for running the leasure side of the camper from the same tank that’s something I wanted to do with my VW but I was told that tanks that had vapor takeoffs on top were illegally to use on a vehicle lpg system,and yes I know they are being made by some firms but that doesn’t mean they are leagal to use on an lpg system.you can use a separate tank with a vapour takeoff and have them linked to the one fill point.
Dave
Whilst good maintainece is the best prevention"If its not broken don't fix it."
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