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#105 by Mark(The Miser)UK on 17 Jan, 2012 19:50
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Hmm there are two fora running amost dentical threads v confusingAnyway, I have a 91 na pump lid on the 91 or 92 TD pump body
That could be your issue. You are missing a stop for the fulcrum lever, but I think it would only effect starting, not running cold.
Can someone explain to me the business of this pintle in the compression tester and it being in different places effecting compression? I'm not getting my head around it.
Also, compression numbers on a cold engine are nearly useless (but not quite) because there is no spec on it so you have no idea what to aim for.
Some compression testers have a pressure release valve down by the mock injector, and some have this valve up by the gauge. The latter one must have a mini one-way deliveryvalve down at the mock injector end that seals the pressure in the gauge and the tubing.
All airspace below this ie in the mock injector forms part of the combustion chamber and , naturally reexpands as the engine piston drops. Thus the bigger that additional space, the lower the maximum gauge reading will be. Cheaper adaptors aparently forget this problem
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#106 by 8v-of-fury on 17 Jan, 2012 20:02
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Prothe adapter and gauge
He's just trying to make money too.. lol I'll add like %5 to my readings .
Dunno Tyler, been running this pump this way daily since June.
The fact that I can smooth it out with a little peddle and the cold start.. leads me to believe I could stand maybe going back up to 1.00mm or higher..? -
#107 by burn_your_money on 17 Jan, 2012 20:16
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What I'm not getting about the compression tester is regardless of where the pintle is, all space above and below it has to get to 500psi (or whatever) at some point in order for the gauge to read it. All that air above and below the pintle needs to be compressed to the same psi. Op, There it is. Thanks guys.
Like I said 8v, I am doubtful that the pump combo was your issue.
I think the fact that more RPMs help is an indication of a compression issue because the higher RPMs will cause higher compression. -
#108 by 8v-of-fury on 17 Jan, 2012 20:28
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Crapp. well I guess i gotta get on that compression check eh?
Hmm really Tyler? I was just meaning like, upping 200rpms.. could that still up the compression that much? So maybe i just need to up my idle then and live with it?
Going off the idle adjustment.. and that your helping this thread, and know some stuffs.. Can you help me a tad?
I have messed with every external setting of my pump so much.. I will try and get a picture of all my adjustments so you can see what I mean tomorrow..
I have a solid main spring in the governor, the throttle one spline ahead/behind whichever was the one to do. The top min throttle screw backed out as far as possible, the side idle adjustment out as far as possible, and the max fuel screw in as far as possible before it hangs rpms... -
#109 by Mark(The Miser)UK on 18 Jan, 2012 05:12
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What I'm not getting about the compression tester is regardless of where the pintle is, all space above and below it has to get to 500psi (or whatever) at some point in order for the gauge to read it. All that air above and below the pintle needs to be compressed to the same psi. Op, There it is. Thanks guys.
Sorry does this mean you understsand the process or not?
Lets assume a brand new perfect engine that is said to be 500 psi on compression. Lets guess that is with a figure of 6ccs of air space. You now attach you gauge with a foot long tube on to where the injector goes. The whole thing is hollow, so doubles the effective airspace. Cranking engine therefore causes the gauge to read about 250 psi, before dropping back down to zero, just like an engine with the injector in. Repeat and it goes back upto 250, but no more, and again drops back as the piston goes down.
Now fit a little flap valve right next to the injector sized fitting. Lets wish for this fitting to be solid, except for a capilliary hole down the middle, which allows high pressure air to rush through but doesn't amout to much air space. Turning engine over will again only charge everything up to that 250psi. However as the piston drops, the gauge and all the air above the valve still reads 250psi because of the oneway valve.
The piston comes up for another go. Now the valve acts like a brick wall and cannot open until the chamber reaches 250psi. This pressure will be reached becuse we know that the normal sized chamber on our good engine reaches 500psi at TDC. We reach 250psi when piston is only half way up the bore. At this point the oneway valve begins to float in limbo as it is subject to 250psi on both sides.
Now the big chamber that includes the gauge and hose, is seeing the 250psi, yet the piston still has 250psi worth of compression left to travel, only again it is having to compress twice the chamber size. Thus for the final half of the stroke the gauge rises approximately half of the difference, say 125psi, so now the gauge is reading 250 +125, or 375psi.
On the next cycle the gauge maygo up about another 60psi. This is repeated in diminishing amounts, until you are pretty close to true compression pressures.
Now imagine you get an adaptor the size of a cotton reel and an internal bore you could stick you thumb in for $2. Now because that volume is underneath the oneway valve, the effective compression chamber always adds that on to the ebb and flow of the compression , and so the gauge never reads above this new enlarged effective chamber size. Yet the actual gauge may be accurate... -
#110 by burn_your_money on 18 Jan, 2012 17:48
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Thank you Mark. I wasn't meaning to sound terribly sarcastic in my last post, I actually did understand it the way you guys were saying it earlier. Your explanation just verifies my reasoning, which helps.
Now if anyone knows where to get the pintle for a snap-on compression tester mine would actually be useful. No wonder all my engines had low compression
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#111 by R.O.R-2.0 on 29 Jan, 2012 14:43
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well, i advanced my timing, and fixed all my air leaks in the fuel system, and now i can glow for 8-10 seconds, pull the CS advance, and hit the key and it fires right up without applying throttle! if its REALLY COLD (20*f is really cold here) i usually have to glow for 15, sometimes 20 seconds before i fire it, then with some afterglow also, until the engine smooths out, and runs nice/doesnt buck..
so, for me, it was an easy solution.. i figured it would have been anyways, because it ALWAYS started PERFECT in my rabbit.. then i did the swap, and it didnt run good at all!
wish i had a dial indicator adapter so i could check my timing tho. i know its very close, timing wise tho, because it starts nice, and has GREAT power.. that could have been from the recent addition of a mitsu starion intercooler tho.. it fits, and quite nicely i might add, but its still HUGE.. i had to swap from a mk2 a/c radiator, to an 84 rabbit doesel non a/c radiator..
if i were gonna do it over again, i would use an even smaller intercooler than the starion unit. -
#112 by jimbobpolo on 25 Apr, 2012 04:17
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I did video of a cold start of my polo Td in -7 deg C.....
http://m.youtube.com/watch?v=9Ny5nR71BeE
Lots of smoke!!