Engine Timing Curiosity

Dick Deegan

Dick Deegan

Well-known member
I have a friend whose engine seems to be running at idle very poorly. The engine rolls - like the timing is too far advanced. Also, it doesn't sound like a Model A. However, the timing seems to be spot on according to the instructions from FS Ignition. This engine was rebuilt recently within the last year.

My question is - what would the engine run like if the timing gears were displaced by one tooth? I believe that the crank gear has 25 teeth and the cam gear 50. If the setup was off by one tooth that means that the valve timing would be off by 7.2 degrees. Would the engine even run?

BTW, rolling down the highway this engine has lots of power - climbs hiss well etc.

Dick
 
Most engines won't run if off a tooth. I don't know about an A though, never tried it. Does the engine start like the ignition is too far advanced ? Does it have some kind of special camshaft ?
 
i have found most engines will run a tooth off with the symptoms being lack of power, lower than normal compression. a proper leak down test will show this
 
Dick Deegan said:
I have a friend whose engine seems to be running at idle very poorly. The engine rolls - like the timing is too far advanced. Also, it doesn't sound like a Model A. However, the timing seems to be spot on according to the instructions from FS Ignition. This engine was rebuilt recently within the last year.

My question is - what would the engine run like if the timing gears were displaced by one tooth? I believe that the crank gear has 25 teeth and the cam gear 50. If the setup was off by one tooth that means that the valve timing would be off by 7.2 degrees. Would the engine even run?

BTW, rolling down the highway this engine has lots of power - climbs hiss well etc.

Dick
Click to expand...


Some of the crank gears from the 70ts were off by a 1/2 tooth. They ran but were low on power.
 
Check out your intake manifold to block seal by dropping oil on the gasket/juncture. You may have an air leak that only running "rich" may cure (and goes away in the mass air flow at full throttle.)

Joe K
 
Patrick: The engine starts right up very easily. It has a Snyder's 5.5 head and I believe the cam is stock.

Dick
 
I will get the owner to do a compression check. I think that he told me that the compression was OK on #'s 1 and 2, but low on #3 and I am not sure about #4. I will get him to redo it. Would it be possible to have good compression on a couple of cylinders and not on one or two?
 
Dick Deegan said:
I will get the owner to do a compression check. I think that he told me that the compression was OK on #'s 1 and 2, but low on #3 and I am not sure about #4. I will get him to redo it. Would it be possible to have good compression on a couple of cylinders and not on one or two?
Click to expand...

absolutely it is possible. The head gasket could be leaking between the two, which would definitely cause rough idle. Or they could both have burnt valves or worn rings. If a comp check confirms uneven compression, have the owner do a leak down test to dial in on the problem.
 
Thanks Pat; What I meant to ask is whether #3 could be low due entirely to a misalignment of one tooth on the timing gears. With the recent work done on the engine I am assuming that the head gasket and rings are OK - but you never know!!

Dick
 
Checked my buddies engine this afternoon and found that you can just see the edge of the cylinder from the spark plug hole. I inserted a very long and thin screwdriver while he turned the engine over by hand. When the timing pin went into the dimple the piston was at TDC. No problem with timing gear misalignment.

Will now chase air leaks.

Thanks for all of the input. Very much appreciated.

Dick
 
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