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MG TD TF 1500 - bronze valve guide clearance
|The sticking exhaust valve reared its ugly head again during the drive to and from the GOF, so off with the head. This happened a couple times some years ago after doing the head, fine since, but the engine did sit for 2 years during restoration so maybe rust on stem also? I have looked everywhere for the correct valve to guide clearance, but can't find it (I know it has been discussed on the board, but "search" fails me). what is is? .003-.004 for the bronze? Thanks in advance, George|
|George - I am not an expert, but I believe that my machinist told me they needed to be 0.001" over the standard. He also told me not to bother with bronze guides as they don't really accomplish much positive. Cheers - Dave|
This was put out on the TABC site several years back from John Bibby, UK based master MG engine builder (John builds engines for a couple of the fastest T-series engined VSCC "specials" -- up to 150bhp!):
"However this assumes that the rest of the valve gear has been lightened as much as possible that
the valve guides are not too tight, if you are using valves with chrome stems and bronze guides I would advise 0.0010-0.0015 clearance on inlets and
0.0020-0.0025 exhaust , and if a road engine stem seals on inlet only and if a race engine no seals at all."
|George, For did many years, Land Rovers had this problem, I was doing 2 jobs a week! We would clean up the guides with a reamer .0002 or so over size. This was not needed on cars that were driven hard, ask my wife, her right foot has 2 positions, on , & off the throttle, 100k on her Land Rover, no stuck valves. My TD had a sticking valve after a perfect rebuild, I was driving like grandma! After correcting a slightly rich mixture, & driving harder, it has not happeded again, 6 years, & 25,000 miles later. Marvel mystery oil will also help.(I did not enlarge the guides on my TD)|
|Talked at length with the machine shop owner that did the head. The initial sticking valve problem was most likely due to a carb problem (debris in the jet causing too lean), but that we did go through the head a couple years later when my crank broke. It had been fine ever since, with a couple longer trips on really hot days, etc. He asked me about the age of the gasoline used. In fact, the first 5 gallons in the tank were purchased last May (from my hurricane/ generator stash). He has been seeing this with some frequency as of late- old gas causing a sticky gunky varnish on the intake valve stems. What do you all think about this theory? Off with the head Friday, so we will know for sure. George|
|George, I don't think it's a theory. I believe it's a fact. I lost a couple of valves on some garden machinery with fall to spring storage. Gas turns south and you get stuck and bent valves. Long storage with gas demands some fuel stabilizer imho.|
|in regard to the varnish theory.. how does it make it through the filters/screens/jets? if the jets were so gunked up how did it start and run? so with this theory the jets would only partly clog but yet the varnish is still able to pass and collect on the valve stem? my limited experience with gas that goes bad is the engine won't start. i agree with laverne about using a stabilizer. i had some difficult times here awhile back and a boat i had winterized and sta-bilized ended up being in cold storage for 6 YEARS. i thought i would have a tank fulll of gunk. i started to siphon the gas out and i noticed it looked normal..took a whiff and it smelled normal. i put parallel fuel filters on it and she fired right up. i started her several times and decided i might as well run her. she has run like a top the last three summers after coming out of 6 years storage. sta-bil is amazing! regards, tom|
|Just a hypothisis on my end Tom, but I suspect what happens is the solvents leave the gas and the mixture begins to break down. You still have a fluid but I think it cooks itself on the valve stem instead of flowing by. eventually it builds up enough of a coating to lose the clearence on the guide and bingo.. bent valves or push rods. I'd have to ask my dad about what really occurs with the gas a he worked in a refinery for over 30 years. |
|George;;; Here is something I might suggest that you try before pulling the head. It has worked for me in many situations.. Lower your crankcase oil by 1 guart and substitute the cheapest trans fluid availble.Start the engine and run it for about one hour. Drain and refill. You could also remove air filter and with the engine running saturate the intake with trans fluid till the engine bogs down. Let set overnignt and restart the nest morning. Be certain to put a sack or cloth over the exhaust pipe to collect the drips and crud thats going to come out. Put cardboard on the floor.If not you will have a black stripe way out back.|
I have used this system for the past 45 years and it has never failed me. This is both in my original marine business and later MG-Jag service.
Cheap trans fluid has a great cleaning ability and if you have a crud build-up on the stems it will help remove it.
This thread was discussed on 14/04/2008
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