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Old 06-03-2012, 07:05 PM   #1
choiceph
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Default hard cranking flathead

hey guys
i have a 239 flathead engine that i rebuilt and now it is hard to crank. i belive tha that it is because of the new piston rings

dose anyone have advice on how to get the engine to turn faster so i can start it
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Old 06-03-2012, 07:11 PM   #2
George/Maine
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Default Re: hard cranking flathead

Well in the old days you would tow it or push it.
You could shim the bearings and when broke in take them out.
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Old 06-03-2012, 07:21 PM   #3
choiceph
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Default Re: hard cranking flathead

thanks george allready though of that . if i don,t have the plugs in the carnk is not as hard so i think it is in the piston rings
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Old 06-03-2012, 07:26 PM   #4
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Default Re: hard cranking flathead

Take the plugs out, put it in 2nd gear and tow it around the block.
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Old 06-03-2012, 08:11 PM   #5
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Default Re: hard cranking flathead

Take the plugs out, lubricate the cylinders and spin it with 12 volts. You may even crank and start it with 12 volts. G.M.
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Old 06-03-2012, 08:17 PM   #6
Mike in AZ
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Default Re: hard cranking flathead

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make sure you have good cables for 6V....good ground/s....then maybe do what G.M. says....can jump the starter direct from 12V battery while everything hooked up to 6V, if that's what you are using....good luck....Mike
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Old 06-04-2012, 02:04 AM   #7
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Default Re: hard cranking flathead

C'mon guys! What's with the ham-fisted, redneck "solution" of pulling the car or needing 12 volts?! If you had bought the car new, did the dealer have to pull it around the block for you? No, it fired right up and away you went.
If it won't crank fast enough to start, something is WRONG! Fix it first.
"Shim the bearings"?? Why?? So you can hear it knock? Maybe the muffler belt is too tight!
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Old 06-04-2012, 02:24 AM   #8
George/Maine
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Default Re: hard cranking flathead

Shim the bearing to get it to turn,this was done by the back yard mechaic.
Some times you would put a .001 bering and would be to tight.
The rich went to dealer.get a ticket if you pulled a car today.
Very common in the 1960s.Then you had to put 2 6volt battery together.
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Old 06-04-2012, 07:12 AM   #9
Walt Dupont--Me.
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Default Re: hard cranking flathead

Well guy, you can do what you want to, but I don't understand why anyone building an engine don't know there is something wrong when there building the engine and it turns over hard. You will have some ring drag but the engine should turn over with a 1/2in ratchet on the front crank without much trouble with the plugs out. With the plugs in you'll feel the piston come come up on compresion but it should turn over with a good 6 volt batt with good fat cables bolted to good clean ground on the block as close to the starter as you can get it. Of course it won't hurt it to spin it over with a 12 volt. If you have ro drag it down the road the engine builder better find another job. Walt
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Old 06-04-2012, 07:25 AM   #10
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Default Re: hard cranking flathead

When I assemble an engine, I turn it one full revolution after each piston is put in. If it gets tight, you know which one it is and remove it to find out why. Back in the sixties, I think a lot of ring sets were just a little oversize to compensate for cylinder wear. I rememebr seeing cars pushed or pulled to fire the first time, when driven a while it would be OK so long as it didnt overheat.
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Old 06-04-2012, 08:21 AM   #11
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Default Re: hard cranking flathead

Walt's got it covered.
While assembling was it difficult to turn over? Did you check main bearing clearance?
Connecting rod clearance? What about the piston ring gap? When assembled and on the engine stand could you rotate the engine with a 1/2" breaker bar or ratchet?
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Old 06-04-2012, 09:46 AM   #12
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Default Re: hard cranking flathead

Like the others have said, it should be free to turn by hand with a 1/2 breaker bar. If it's not, you have a problem that towing or high voltage won't fix. Even if you got it running, you're probably going to cook something.

On assembly the engine should be rotated by hand after each component is installed/torqued. I did a job where the main caps were swapped. As soon as I torqued the cap the crank got bound up.

The opposite is true when trying to diagnose the problem. Each cap should be loosened and the engine rotated to find where the binding is.
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Old 06-04-2012, 09:52 AM   #13
George/Maine
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Default Re: hard cranking flathead

When you are using new rings and old pistons most of the time there is carbon in the ring groove.Some cheap motor jobs was to use under size bearing .001 or .002
Cheap motor job is what you get.Nice to have new stuff.If in car and all together put 12 volts to it and no sparkplugs and oil good,if oil pressure keep it going for a while,take a break and do it again.
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Old 06-04-2012, 10:05 AM   #14
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Default Re: hard cranking flathead

Quote:
Originally Posted by choiceph View Post
hey guys
i have a 239 flathead engine that i rebuilt and now it is hard to crank. i belive tha that it is because of the new piston rings

dose anyone have advice on how to get the engine to turn faster so i can start it

When did it start to get tight.You have an assembly problem going on there.
Towing or 12 volts won't cure your dilemma.Was the engine completely rebuilt?
Bored crank ground.Or re ringed only.The engine must be able to be turned by hand with ratchet things are at fault.You could have an oil ring rail hanging up due to a poor installation.Starting it with that will be a sure failure.Keep us posted to your findings.What did you use for a ring compressor.What were your ring end gaps?Too many unknowns.Ignore the lame postings about towing it that is a disaster waiting to happen.All this is based on the starter being serviceable and you confirming the engine is hard to turn by hand with the plugs out.
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Old 06-08-2012, 08:20 AM   #15
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Default Re: hard cranking flathead

BTT is it fixed yet??
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