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I have a mf 35 4 cylinder engine rebuilt pistons liners rings little ends
valve seats recut new valves head skimed it used to start up on 3 cylinders then the 4th cylinder come in we have had the injectors and injector pump serviced now it takes up to 4 atemps to start even in hot weather, if it was cold don’ go there because it won’t start. Heater plug is working only got 1.
I suppose it must be something to do with the injection timing. Did you have a look at the timing chain and tensioner and also the backlash on the injection pump drive gear?
No we didn’t look at the timing chain or the tensioner or the backlash of the injection pump, one thing we did do is to check the compression 120 psi when dry and 190 psi when wet,do you know what the compression should be please. Many thanks, Phil butler
I’ve been searching for the compression test data which I knew I had somewhere but just couldn’t find. Anyway I’ve found it now.
The data I have is that the dry test should be 380PSI and then the wet test no more than about 10% above this. I would think that anything above 350PSI would be acceptable.
The dry figure I have is considerably higher than yours, but you have had new pistons, liners and rings. Did you fit the rings yourself? Were rings 2 and 3 fitted with the tapered periphery of these rings towards the crown of the piston?
The good news is that there is a difference between your two tests so that eliminates the cause of your problems been with the head gasket or valves.
However, the difference between your dry and wet tests is quite a lot, which all points towards a problem with either the liners or the pistons/rings.
Did you do the compression test on all 4 cylinders? and observe similar results.
I believe your compression test is very low, so I would think this is probably the cause of your starting problems.
Just a thought. Have you connected your tester through the injector fitting with a clear passage from the cylinder to the guague? Did you turn the engine over so the test gauge gave 5-6 readings before taking the reading?
I haven’t tested lots of the 23C engines myself, so I haven’t got any data of my own to compare with your test results. The 380PSI I quoted was a ‘text book figure’ I once wrote down, but I think it is about right.
120PSI is certainly low.
I have a to35, 1959. MF gas tractor
I did a compression test on my tractor.
I took the frount plug out and hooked up the tester and started the tractor. Gauge read 55 lbs.
replaced the plug, and removed the second plug. It read 60 lbs.
replaced and third plug read 70 lbs.
replaced and 4th. one read 65 lbs. Did I do it right. was readings low.
Hi All, I have fitted new pistons, liners, valves, injectors, pump ETC. to my 23c and she is now very hard to start and smoking badly, I’m pretty sure the timing is set correctly and I have set the pump timing a dozen time trying different settings with no improvement. The smoke is blue indicating unburned fuel, i’m now runnibg out of ideas and would like to check the compression. All the standard compression testing kits seem to cater for injectors with clamp bolts either side of the injectors, the 23c has the clamp bolts slightly below the injectors and use an L shaped clamp. Does anyone have either an adaptor for this or a compression testing kit I could borrow for the job? I Live near Telford, I could either collect or I will pay the transport cost.
Very interesting reading. I’m going to compression test a friends MF35 this next weekend as it’s an appaling starter and is using a lot of oil when comp ploughing (pressuring the crankase – heavy breathing through filler and dip stick) so I suspect rings. It’s had a re conditioned head on it about a year ago so this should be pretty good.
I’ll test to the pressures you’ve experienced above although 400+ sounds high. Are the engines above a four cylinder standard or a Perkins version? He has a standard engine so I’d like to know if these pressures are relevant. Many thanks Rich
Are we all measuring the compression in the same way? That is, with our non-return valve in the same place so we trap the same tdc volume as the next guy???? On high CR engines lost volume causes a more significant error.
I have now measured the compression on my tired old 23C. I get 380,440,420,420 psi. Isn’t that something like 28:1 CR? Is this not way above spec?
I have measured this with a Gunson hi-gauge. The threaded bit of the tube that normally goes down a spark plug hole just fits down the injector nozzle counterbore and the o-ring just about goes down too. The plain shank doesn’t but that’s good as it holds the o-ring down. (Ok the couterbore may be a bit rough and the corner may mash the o-ring after a few goes but I get the numbers.) This puts the non-return valve as close to the true volume as possible as the nozzle insertion depth is similar. This was held down with a modified injector clamp. A vee was cut in the pad to allow the hi-gauge hose thru whist keeping the tube perpendicular and a slotted m16 nut used as a spacer under that. The nut may splay open and ride down the plain shank of the tube so improvise further!
****WARNING**** The FSD of the gauge was exceeded so i put one with 600psi FSD intead. Keep volume of adaptors as small as possible to reduce the number of compression strokes required to reach a steady reading.
****ANOTHER WARNING**** If the hardware explodes or pops out then bits may hit you so take precautions.
How is everyone else doing it?
Can we all agree on a standard (pun not intended) compression test method?
SO.. I get bad starting. I also get bad idle smoke and lumpyness. A bit like the “before” 23C on the DVD. Can I rule out bad compression? Rather not remove the head unless i have to.
Re 4cly 35 possible reason for low compression could be valves seated to low in cly head might need a few inserts fitted?
More info here, from Dave’s 23C engine.