1919 Roadster center main knock??

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Model T Ford Forum: Forum 2017: 1919 Roadster center main knock??
Top of pagePrevious messageNext messageBottom of page Link to this message  By Jonathan Delancey on Thursday, January 05, 2017 - 07:20 pm:

Happy new year everyone! I have a 1919 T roadster that has a bit of an engine knock. First off, when I short out the plug closest to the driver, it knocks constantly, when I short the next one it pretty much stops, and shorting the next doesn't change much, and shorting the plug in front doesn't change much either.
It only knocks when at a low (normal) idle. When the engine is revved up at all it goes away and sounds great unless you short the first plug.

Even under a load it sounds great. My dad took up the rod bearings (maybe not enough). I know it sounds like a rod knock, but I'me not going to get my hopes up.
What could it be, and can I keep enjoying her? Thanks (:


Top of pagePrevious messageNext messageBottom of page Link to this message  By joe bell on Thursday, January 05, 2017 - 07:37 pm:

If you take up the center main, take the front and rear up also, if you do not the crank will be flexing and later on you will join the two piece crank club. Use plastic gauge to know where you are at. Hope this helps,


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Thursday, January 05, 2017 - 08:14 pm:

When shorting out spark plugs seems to change the knock situation, that would seem to indicate a rod knock, however, just for the heck of it, check for loose crankshaft pulley and also the pin. A loose crank pin (hand starting crank pin) can work it's way out until it begins to strike the pan snout, and that can sound just like a rod knock. Not sure if "snout" is a good term, but you know what I mean,....the narrow cup shaped very front of the pan right under the pulley.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jonathan Delancey on Thursday, January 05, 2017 - 08:22 pm:

Thank you! But what does it sound like it is (according to my description)
And since the #1 and 3 main tends to wear in the cap, and #2 (center) tends to wear in the block,
wouldn't you still be bending it up if you tried taking shims out, because of the lesser Babbitt on the block side of the center main?
And I am sure the mains don't wear evenly, so taking up all 3 (evenly) would be tricky. ??


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jonathan Delancey on Thursday, January 05, 2017 - 08:29 pm:

Sorry, my last message was pertaining to Mr.Joe Bell's message.
Thanks, I will check the pulley/pin, although I'm sure they are OK.
I think "snout" is a perfectly good term to use! (:


Top of pagePrevious messageNext messageBottom of page Link to this message  By keith g barrier Savannah Tn. on Thursday, January 05, 2017 - 09:50 pm:

The center main does tend to whip the Babbitt out of the block but maybe you will be lucky and get by for a while by taking them all up. KGB


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Lloid on Thursday, January 05, 2017 - 11:46 pm:

Seems like a lot of stuff is trial and error with a worn part or it has been for me. You could take up the difference one at a time but it would be a lot of work to put it together and try it and repeat the process, hey but if you had the time to do it you could figure out that way.IMHO Tim


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Menzies on Friday, January 06, 2017 - 11:37 am:

I would suggest the rear main is warn and thus causing the crank shaft to "whip" in the center. If not tended to it will break the crank shaft. With a warn rear main and shimming the center main will only cause greater stress on the crankshaft. The crankshaft should be removed checked for straight and straighten it if bent, then re-establish the bearing/crankshaft alignment. A friend of mine was touring the back roads, miles back in, and when pulling up a hill the crankshaft snapped in the middle.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Dallas TX on Friday, January 06, 2017 - 11:52 am:

If it was my car I would pull the pan and inspect the rod bearings. If it is not a rod bearing causing the trouble then pull the engine and fix the mains. If it is a rod bearing then you can easily pull shims or replace the rod(s) that is / are worn with overhauled ones.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Friday, January 06, 2017 - 11:54 am:

It doesn't sound like a centre main to me. Anyway I have adopted a policy of removing the engine and doing the adjustment on the bench. In regards to checking the centre main, I install a dial indicator to the journal and then press the crank against the block. Usually I have found the wear is just in the cap. IF it is worn in the block then it seems that usually the pan is bent. If it is worn in the block then I first check the crank for straight. If it is straight then I undertake the needed work to either redo all the mains or scrape the other mains until I get no deflection on the dial indicator test and have a good bearing surface on all three mains.
All this being said, your symptoms don't sound like centre main to me


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jonathan Delancey on Sunday, January 08, 2017 - 08:13 pm:

Thanks everybody, I will need all the help I can get on this one! I will check the rods again with plastic gauge. I REALLY hope it is not a main, I don't think I have the know-how,

the tools, the time, the MONEY, to pull the engine for a loose main. So it only knocks when it misfires on the last cylinder(every once in a while), and constantly when I short it, why is this? And if I could get it to not misfire it wouldn't knock, I guess? I would love to keep
driving her, and not have her in a million pieces for a year, or THOUSANDS of dollars into it for an "overhauled" engine!! Are there any T engine mechanics on here? If so, I would LOVE to here what you think, and if I must
"overhaul" it to drive it any further. Thank you so much!


Top of pagePrevious messageNext messageBottom of page Link to this message  By John T. Tannehill III, Hot Coffee, MS on Sunday, January 08, 2017 - 08:54 pm:

Jonathan knowing that you're a high school student I hope it's just a rod but most everyone with a model T sooner or later becomes a t model novice mechanic. The folks on the forum have tons of experience. They will be able to help you remotely, you will have to provide the labor. I'm sure there is someone close by that will step up to help but don't be afraid to get your hands dirty. You'll have a blast, a learning experience and then the ability to tackle the next problem.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jonathan Delancey on Sunday, January 08, 2017 - 09:07 pm:

Thanks for the encouragement! I guess all i'me afraid of is really messing something up,
like putting it back together and then becoming a member of the 2-piece crank club sometime later, or nicking a field coil! ect. ect.


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