Valve Timing

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Model T Ford Forum: Forum 2011: Valve Timing
Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, July 14, 2011 - 07:24 am:

When you are fortunate enought to find an old engine with good main bearings and decide to install 4 modern valves, should the valves be timed by the piston position method or can the valve clearance be set to a specific gap?

What should that gap be when using an original camshaft?

This engine in question seems to have good performance on #2 and #3 and randomly sneezes through the carb on #1 and #4, but mostly on #4.

There are a few theories as to the reason for this performance.

Could the camshaft be a tooth off and have the engine start easily on Bat or Mag and have two cylinders appear to have normal power?

Could the front plate be positioned off in such a manner that only cylinders #1 and #4 could be affected?

Could there be another reason for this performance, when all the spark and gas components have been totally swapped out with the symptoms remaining unchanged?


Top of pagePrevious messageNext messageBottom of page Link to this message  By John Gelfer on Thursday, July 14, 2011 - 11:59 am:

How about timer misalignment?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush, Portland Oregon on Thursday, July 14, 2011 - 12:31 pm:

You will need to time by piston travel if you have the nonadjustable lifters. You are setting the valves to open and close the same for all cylinders so your gap will very. If you have the Service Manuel or Murray F. repair books they will guide you through the process.
Have you check the compression?
If you are going to take the time to replace 4 valves, why not save the later headache and replace all of them?
I would think that if the timing gear was off by one tooth, all 4 would show the same symptoms.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, July 14, 2011 - 02:24 pm:

A good catch Mark. 8 valves were replaced. I have always used .012 Intake and .014 Exhaust for stem clearance, but I have always used a reground camshaft, which has the smaller cam area or back side ground thinner for more lift.

Unfortunately, I do not know the size of a standard original camshaft to determine if wear might be a problem.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. Golden on Thursday, July 14, 2011 - 02:27 pm:

Compression is 46 46 46 48. The pistons and rings are also new and not seated yet. Would compression still be that good, if the cam was a notch off?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Weir on Thursday, July 14, 2011 - 03:34 pm:

I believe the cam timing can be a tooth off and not make a lot of difference when firing up a fresh rebuild. When 1 & 4 are both @ TDC one of the two should have nearly the same clearance or the same lift off the seat. In other words, in a simple cam profile and timing arrangement like the 'T' , there should be little or no offset in the Ex closing and the Int opening.

Sincerely

Jim Weir


Top of pagePrevious messageNext messageBottom of page Link to this message  By Norman T. Kling on Thursday, July 14, 2011 - 08:02 pm:

It's a good idea, if you are going to use the valve timing method, to also check the clearance to be sure it's not too close. Likewise if you set the clearance, double check to see how close the valve timing is. A lot can change over the years due to wear, block decking, camshaft grinding, etc, and if you don't know the car's history, it is a guess unless you double check. On my car, it was set by valve timing, but when I did some further work, I adjusted by valve clearance, and found it had more power. Using the valve timing method, some valve clearances were as much as 30 thousandths. That didn't give as much lift.
Norm
Norm


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Walker, NW AR. on Thursday, July 14, 2011 - 08:02 pm:

"Unfortunately, I do not know the size of a standard original camshaft to determine if wear might be a problem."

Jim -- Use a micrometer to measure the difference between the smallest and largest dimensions on each cam lobe. Originally the difference was .250", so you can see how much less than that they are.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush, Portland Oregon on Thursday, July 14, 2011 - 09:27 pm:

Worn cams and unknown lobes are part of the reason that you use piston travel to set your valves.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank Harris on Thursday, July 14, 2011 - 09:57 pm:

If you are working with old worn out parts use the piston position method if you know the deck has never been re-surfaced and you have stock original Ford cast iron pistons.


On the other hand, if you have a good cam shaft and adjustable lifters you throw away horsepower for every thousandth's of an inch you add to the gap. 010" and 012" are good and if you want to beat the other guy go 006" and 008". The guys that piston position the valves with worn out cams like to get .035" gap and just love to listen to the clatter as they go down the road in the right hand gutter.


Retarded cam will give you low end torque and advanced cam will give you higher top speed.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. golden on Friday, July 15, 2011 - 06:19 pm:

I took four old cams and measured them with a micrometer. The measurements all vary and I don't know if any or all of them have been reground.

The average small or cross-wise value was .812 and may have been .8125 originally.

The average lobe value was 1.05. That would provide a lift of .2375 or just under the .250 of the new stock Stipe cams.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money, Braidwood, IL on Saturday, July 16, 2011 - 03:18 am:

I'm curious as to the comments about using piston position method if parts condtion are unknown. Why would this be better than using clearance method? Just trying to get a picture of this in my head.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Or on Saturday, July 16, 2011 - 03:37 am:

I will start by saying, not all lobes on the cam will wear the same. The goal of setting your valves by piston travel is to get them to open or close at the same/right time. This method works esp well if you still have the original lifter in the motor. The tops will be cupped from years of pounding and can't be set by feeler gauge with out removing and facing the tops.
Even if your block has been decked the instructions in the MTFCA engine book gives detailed instructions on how to find the lowest and highest point that the valves open or close to set them up.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Saturday, July 16, 2011 - 03:42 am:

Frank said: "Retarded cam will give you low end torque and advanced cam will give you higher top speed."

I think in general, the opposite is true.


Top of pagePrevious messageNext messageBottom of page Link to this message  By James A. golden on Saturday, July 16, 2011 - 09:36 pm:

Doug, the clearance method is evidently OK with a new precision ground cam, but some early cams were not ground that close and some didn't wear exactly the same. In either case, a close check with the piston position tool would have saved a lot of grief and extra work.

The real problem in this case was identified and fixed today. The crankshaft gear did not have a recognizable timing mark or it was off a tooth. The intial problem was that the engine ran so well with just #2 and #3 that it was not easy to accept the fact that the camshaft was off a notch.

Now, there is a similar problem with another engine that runs smooth at idle and backfires in high gear or under a load. There are presently no clues or suggestions as to why that could happen.


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