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Author Topic: dk with the shakes  (Read 476 times)

lewis66

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dk with the shakes
« on: July 04, 2019, 02:21:36 PM »
 i have just over hauled a dk which  had the factory conversion fitted and still had 2 head gaskets , it ran fine but needed a good decoke  , i fitted a flat top piston just to make it correct and it runs fine but it shakes , crank / flywheel run true , timing spot on it is a 2hp 1000 rpm engine with the smaller flywheel , its ok at 750/800 rpm so might just change the gov springs , has anyone got any ideas ? my other 2 ''d's '' run dead smooth but are both 1.5hp 750 rpm units

mike90045

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Re: dk with the shakes
« Reply #1 on: July 04, 2019, 03:16:57 PM »
I'd look at the piston weight, since that's what you changed.  Was one iron and one aluminum ?   Weight change makes unbalanced vibration.

lewis66

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Re: dk with the shakes
« Reply #2 on: July 04, 2019, 03:39:54 PM »
both cast iron

BruceM

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Re: dk with the shakes
« Reply #3 on: July 04, 2019, 04:59:01 PM »
The new iron piston is clearly a different weight.  You'll have to add or subtract external counterbalance to get it running smoothly at your desired rpm.  If it's a hopper, then add more counterweight.  If it's a walker or moving fore and aft, it's got too much counterweight, so add opposite the counterweight. 

lewis66

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Re: dk with the shakes
« Reply #4 on: July 04, 2019, 07:08:23 PM »
hi yes i  totally agree i guess that's why lister didn't include the piston in the dk conversion kit , i got the engine from the original owner who had it new in 1949 and fitted the kit , i presume listers balanced the engines according to spec ,   

cobbadog

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Re: dk with the shakes
« Reply #5 on: July 06, 2019, 12:13:49 PM »
What was this kit suppose to do?
I find it very strange that a factory part requires 2 head gaskets. Governor weights should not make any difference to balance of an engine only rpm to my way of thinking. Vibration issues will go back to major moving parts from crankshaft to flywheels. It would be rare that a flywheel would be out of balance after all these years and the crankshaft should show a wobble either up and down or left to right.
I would remove the spark plug and set up a pointer on the outer rim of the flywheel to see if it is hopping up and down then do the same for a wobble left to right. Adjust the pointer so that it touches and slowly rotate the flywheel and it should stay touching. DO this both ways as described and then you will know that is correct and start looking elsewhere, but I feel it is in this area somewhere.

Keep us informed on the tests and progress.
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glort

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Re: dk with the shakes
« Reply #6 on: July 06, 2019, 02:02:06 PM »

Might help to weigh the 2 pistons as well.
Just because they are made from the same material does not mean they weigh the same. Production parts can vary by a lot even when they are the same design and out the same box. Same goes for tolerances. 

I have seen plenty of new parts that were out of spec when they were gone over and measured.

lewis66

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Re: dk with the shakes
« Reply #7 on: July 07, 2019, 11:38:30 AM »
hi it was fine until i swapped the piston for a flat top dk one , the factory dk conversion kit did not come with a piston they supplied 2 head gaskets to lower the compression , i know the history of the engine and conversion as i bought it from the original owner , i just thought as i was servicing the engine i would fit the correct piston , i think its appart time and weigh it 

cobbadog

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Re: dk with the shakes
« Reply #8 on: July 07, 2019, 12:06:59 PM »
If this is a single cylinder engine the weight of a single piston will not throw it out of balance. What is the reason to lower the compression ratio? Is it to use a petrol/kero fuel mix?

I still think there is something else at fault but try putting the old piston back in and give it a run.
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lewis66

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Re: dk with the shakes
« Reply #9 on: July 07, 2019, 12:52:37 PM »
yes the dk runs a lower compression , my other 2 'd' run fine after overhauls ,but there's all ways one that fights back ! . i will investigate and report back

cobbadog

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Re: dk with the shakes
« Reply #10 on: July 07, 2019, 01:16:04 PM »
These toys are always trying us out. I can't begin to tell you the fun I have had sorting out issues in all kinds of engines, but it is so satisfying once it is sorted and when you find it you believe how simple it was.
Good luck with it.
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lewis66

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Re: dk with the shakes
« Reply #11 on: July 09, 2019, 11:29:05 PM »
update  i have run /adjusted the engine and as long as it is set at at 750 - 800 rpm it's fine so i will run it at that and leave it alone

cobbadog

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Re: dk with the shakes
« Reply #12 on: July 10, 2019, 06:53:26 AM »
that's good news that it is getting to that rpm. So after that it starts to get the vibration which makes me think the issue is a balance problem with the flywheel or it is jumping up and down ever so slightly. This could be established by fixing a screw driver shank near the flywheel on the od and the side ot see if it is jumping or wobbling. It only has to be a small amount for the issue you are having. Even if the flywheel is not quite sitting straight on the shaft because the gibb key maybe moving it off the shaft.
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lewis66

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Re: dk with the shakes
« Reply #13 on: July 10, 2019, 10:30:46 PM »
the flywheel has not been off and runs true and there is no play in the bearings in any direction i am therefore convinced its the piston weight judging by the way it literally jumps up and down and it's the only thing i changed from the original set up which ran ok at 1000 rpm 

glort

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Re: dk with the shakes
« Reply #14 on: July 10, 2019, 11:41:34 PM »

If you knew the difference in the piston weights, it would be real easy to get some wheel balance stick on weights and add them to the flywheel to counteract the difference. Could also just try adding weights by trial and error till you smooth the thing out.
I doubt the difference could be that much so it shouldn't take a lot to do.