Bore Cylinders?

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Model T Ford Forum: Forum 2013: Bore Cylinders?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Rowland Smith on Monday, August 12, 2013 - 07:22 pm:

How do u tell if you need to bore cylinders or just new rings? Engine ran good but had low compression of around 30 on each cylinder...no power, but would idle good. At point of pulling cylinders and need to decide which route to go. Thanks. ( also deciding about new valve seats...help here appreciated.).


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Monday, August 12, 2013 - 07:58 pm:

Easy way, remove the pistons and measure the bores with a dial bore guage to determine wear.

I don't have a dial bore guage, so I use a snap guage and a micrometer.

If the valve seats are so worn that the valve job cannot be done properly then you might have to pull the engine to have seats installed by a shop. Alternatively you can install oversize valves. Same is true if the valve guides are shot, you can either install bronze guide liners or oversize stem valves.

Bottom line if you don't know how to measure for piston diameter you may be better off seeking professional help. Precise measurement takes good equipment, good experience, or preferably both.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Weir on Monday, August 12, 2013 - 08:17 pm:

What is the altitude of Monument Co ?? If it's above 5000' it will make a noticeable difference in the gage pressure shown.

Jim Weir


Top of pagePrevious messageNext messageBottom of page Link to this message  By Rowland Smith on Monday, August 12, 2013 - 08:41 pm:

We are at 7400'


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Garrison_Rice Minnesota on Tuesday, August 13, 2013 - 12:06 am:

Instead of a using a snap gage try using a telescoping gage and a micrometer. A snap gage is for measuring outside diameter. "Bottom line if you don't know the difference between a snap gage and a telescoping gage you may be better off seeking professional help. Precise measurement takes good equipment, good experience, or preferably both."

I apologize Royce, I couldn't help myself. I fully understand why you would call them a snap gage but it's about the same type of mistake that's made when someone calls an optical comparator a shadowgraph. Which by the way is a very precise way to measure an outside diameter when properly setup with gage blocks. Which are sometimes called Jo blocks or Johannsen blocks and often called weber blocks.

So always assure your variable gages are properly calibrated using masters that are also calibrated and traceable to the National Institute of Science and Technology (NIST) standards, and always assure you know what gage to use and what the proper nomenclature for each gage/instrument is. Oh by the way, I always used Boice bore gages. They weren't too hard to set as long as a a person had a good gage block set and knew how to "wring" the gages.

Did ya miss me?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Tuesday, August 13, 2013 - 01:12 am:

You could use feeler gages and check the piston clearance at top and bottom of cylinder.

You need to check crankshaft end play. If its too much, then you need a rebabbitted main cap or to add some babbitt to the thrust surface.

Wear limits are in the T shop manual, if you don't have one then you should get one before you take any drastic action.


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