question about top dead center
05-09-2009, 05:36 AM
#1
question about top dead center
My engine has good compression with the plug in. But if i take it out and rotate the flywheel to tdc its like the piston almost stays there and the flywheel has play in it like it will move back and forth about a eigth of a inch while it seems the piston is not moving at all. Almost like its clicking back and forth at that point without any compresion. But i can feel just a tad bit before that point. This is with the plug out. Is this normal? sorry for all the questions.
05-09-2009, 06:46 AM
#2
bumpity
05-09-2009, 07:13 AM
#4
How old is this engine?
05-09-2009, 08:02 AM
#5
A tiny bit of play is unavoidable, if it's excessive then the rod bushings are worn. A usual running symptom of this is an engine that otherwise runs well but idles inconsistently and goes through glow plugs quickly. If you think the play is more than a tiny bit, replace the rod.
05-09-2009, 08:48 AM
#6
05-09-2009, 09:40 AM
#7
Tech Master
Little play is normal & is refered to as piston dwell time time in real car motors basicly relation of piston moving in a verticle plane & big end of rod moving in a mostly horizontal plane. When you build a hotrod motor most people look for longer dwell time for a torque application by using a piston with the wrist pin hole higher than stock so they can use a longer rod & increase piston dwell,so what I'm saying is its not always a bad thing. This is the motor you just had uh problems with correct? You can pull the back plate off & do the same test & look at where the rod & crank pin meet.If you can see the crank move inside the rod much you got problems & by move much I mean if you can see the rod gush oil out between the space between the 2 then suck it back in when you turn the other way thats the beginning of the end.V-spec crank pins have proven to be uhh less than hard enough there.The good news is once that starts you'll know within a few fuel bottles(500cc bottles)by exactly what Davidka described & soon wont be able to keep it tuned,only with my personal v-spec a new rod did not help much as the bronze bushing in the rod seems to be harder than the steel crank in a v-spec.
Be creative with the search function & you'll come up with more symptoms of this problem & see what the people did to fix it like tune was off or crank was replaced or they just freaked them selve out & motor was fine.You can ebay cranks between $35-60 fairly often if you need to,just make sure you need to before you do cuz like I said some movement is normal & I wouldnt have even said anything if I hadnt read some of your other posts.
Be creative with the search function & you'll come up with more symptoms of this problem & see what the people did to fix it like tune was off or crank was replaced or they just freaked them selve out & motor was fine.You can ebay cranks between $35-60 fairly often if you need to,just make sure you need to before you do cuz like I said some movement is normal & I wouldnt have even said anything if I hadnt read some of your other posts.
05-09-2009, 08:38 PM
#8
I do all of my "degree wheel" timing via a spread sheet & measurements of the various engine components. On a spread sheet it's easier "see" the dwell time and track the piston's acceleration and deceleration as the crank goes through its rotation.
05-09-2009, 09:36 PM
#9
conecting rod and crankshaft are fine. After all i put my engine through it is normal after all. I can stop being paranoid now
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