Thread: No.2 down on compression: 2 1/4

easy to check if youve got an air compressor and a blow gun with the big round tapered rubber nozzle. (or something that will let you get a good seal on the plug hole)

run the engine to warm it up...

remove the rocker cover pull the #2 spark plug then get #2 at about TDC on compression (#3s rockers should be on the rock or alternatively you'll feel a slow breath of air out of the spark plug hole, use the crank handle to turn the engine).

confirm that #2 rockers are free by giving them a wiggle, they should rock up and down the presecribed 10 tho but more is ok for this test. if they arent free recheck the engines position and then unwind the tappets enough to get your movement

put the rocker cover back on and pinch it down finger tight, remove the crank case ventilator, the air horn off of the carby and check that the oil fill tube and dipstick are sealed up (if in doubt remove the caps, apply gladwrap and then use an elastic band to secure)

apply air to the sparkplug hole (50-60psi)

an air his out the carby is a badly seating inlet valve, the exhaust pipe the exhaust valve and the ventilator would be shot rings.... bubbles in the coolant dead head/gasket.

The engine may want to turn when you apply the compressed air so once youve got your engine in the position you want to check put it in gear and apply the park brake...

You may not be loosing compression right at the top so once youve confirmed that its not the head or valves have a friend (2 works much faster) depress the clutch while you or a second helper turn the engine over very slightly then redo the air thing.. pulling all the plugs will make precise movements of the engein possable.

if you get more air in differnt positions of the crank you have an out of round bore, scoring issues or rings that arent playing the game and are on the way out...

depending on how much air is getting past the vlaves removing the head (not that hard if you know your spanners and have a torque wrench) you may get away with an inhead relap using coarse then fine lapping pastes.

hope thats helpful....

Well dave
I have heard and read of a lot of variations to the compressed air trick, mainly redoing valve stem oil seals.
But this one has to rank as one of the easiest ways of checking a number of probs.
well done.

john

I should have added...

if its coming out the valves if you pull the manifolds and the rocker cover then (get a helper to make it quicker) you can try this as a quick fix for carboning /fouling of the valves.

1. rotate engine till the valve you want to work on is fully opened
2. apply compressed air to the plug hole for that cyl with about 25psi and a good flow rate ( a 1.5hp compressor on free delivery is about right)
3. insert a piece of coathanger size wire into the port and use it to scratch at the valve
4. remove the wire and rotate the engine till that valve is closed and the rocker is free
5. using a pair of strong needle nosed pliers or circlip pliers put the tips in the grooves of the collets and rotate the valve on its seat
6. open the valve by rotating the engine again and repeat above untill you think youve got the valve cleaned.

if you feel the wire jagging you have a badly carboned/cracked valve

rotate the engine untill that valve is closed and spray carby cleaner/brake cleaner into the port and let it sit for a bit

redo the above but before you start apply the compressed air to the plug hole.

if its fouling you should get black crud in chunks coming off of the valve. if you do redo the original test and if theres an improvement keep at it. ITs never going to be as good as a head off valves out clean up but It will get you home

If you get no change after a couple of shots of cleaning then its time for a proper revalve... but at least youve confirmed whats wrong and can get a firm quote or know what parts you have to buy for a DIY.

if your getting blowby into the crankcase put a teaspoon of oil into the plug hole, turn the motor over 4 times by hand and recheck at the point of most blowby (tdc and BDC if you cant easily tell the difference) if the added oil stops it then its a rings/carbon siezing of the rings thing.

given its a 2.25 if youve been running it on some of the LRP's, it hasnt had a good long run in a while, youve been letting it idle for ages at a time I'll tip its the exhaust valve not quite seating properly... if the above doesnt bring any junk out pull the rockers off and with a very small hammer using a brass/hardwood drift give the top of the valve stems a few little love taps, turn them using the pliers on the collets trick and repeat, then check the compressed air again (with the rockers off it doesnt matter where the engine is.

in my experience (and excluding abuse/mechanical failures) its normally the #4 rings that wear out on a well used 2.25, #1 if it does a lot of short startup /shutdown sit the go again driving (the runs where the temp guage doesnt get out of cold before its allowed to cool down again) but theres not a lot in it sort of like saying that your head and shoulders get wet first when you have a shower... They do 90% of the time but not by much.

Compression can only escape via two routes. ( normally)

Past the piston rings.
Past the valves.

Check the compressions with the engine at normal operating temperature.
If any cylinder is low: squirt a few cc's of oil into it and re-test.

If the pressure increases substantially the fault is with the piston or rings.
(The exess oil will temporarily seal the rings)

If it remains the same, the valves are leaking.

An air test will then isolate the inlet or exhaust valve at fault.

Hope this helps.

Davy

"easy to check if youve got an air compressor and a blow gun with the big round tapered rubber nozzle. (or something that will let you get a good seal on the plug hole)"

If you knock the ceramic bit out of an old spark plug and then weld, or solder a piece of pipe into the hexagon, you can screw the plug into the plug hole and clamp an air hose onto the pipe - a perfect seal!

cheers Chazza

Never worked on a 2.25, but it can't be that big a job to pull the head and have a look?