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Discussion Starter #1
well, i did a compression test today because ever since i blew the head gasket its felt weak out of boost.

results cyl 1 to cyl 4

dry wet
135 180
140 185
140 185
090 180

cylinder walls are good, i checked with my borescope, piston tops look excellent and there are no signs of oil in the cylinders. so i'm pretty sure when i blew the headgasket and overheated the ring tension was lost....

the car at 15psi still feels great, out of boost feels like its way down on power, but interestingly it idles smooth as stock..... compression test were done on a stone cold engine with throttle open.. after the dry test i was hoping the wet test was the same or similar meaning valve/head issue, but NOPE......

picking up a GSR swap sunday, going to build that and swap it in.... i'm not leaving the forum though sorry!
 

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Classic Man
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compression test should be done on a fully warm engine. with no fuel coming from the injectors. with the throttle wide open. and spark plugs removed.

4 compression strokes, and that is your result.
 

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Discussion Starter #6
i always keep it spinning until the gauge stops, unless its obvious there is a problem, i let it spin about 6 times each cylinder. the gauge stopped on each after 3-4 turns. i was at work, between cars so i didnt have time to warm the engine, not that it would matter anyways, the rings are obviously trashed.

i'd just like to know why they went bad. i've overheated tons of hondas and never had low compression afterwards, and built dozens (literally) of D and B engines and never an issue, until this one, i rushed some important steps to get it going so i can only blame myself.

i'm still driving the car, and it still breaks loose 3rd gear at 15psi so its definately still making power, it just feels like a tank out of boost.... still getting 25mpg driving it hard most of the time..
 

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compression test should be done on a fully warm engine. with no fuel coming from the injectors. with the throttle wide open. and spark plugs removed.
this.

cold numbers, dry or wet, dont mean much.

loose ring? probably. could seal up when warmed though, as a few have done for me. burn/smoked a bit when started, perfect (good compression, leak test good) when running and warmed.

get a b-series, most of the forum has them anyway...
 

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You might have stretched the ring lands
 

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Im Bringing TSEXY Back!
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Either way if you have a good deal on a GSR do it!
Great engine on boost and will take a beating.

Miss my old turbo GSR.
 

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Formerly weebeastie
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which important steps did you skip? Setting the end gap on the rings? Rings could be lined up causing an issue or poor end gap, or just too much heat and the oil rings lost their tension.

What kind of pistons are you running?
 

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If the cars still making good power in boost when the cars warm I would atleast redo the compression test when the cars fully warmed up and then go from there... is the motor smoking any in boost? Or out of boost?
 

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on forged pistons?
Yes, they are stronger than cast aluminium, but they are still aluminium which gets pretty soft in an overheated engine.

It is most likely lost tension in the rings which are steel or cast iron and a lot stronger than aluminium at elevated temperature. Ring lands stretch if it gets hot enough for the ring ends to run out of gap and start to seize in the bore.
 

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If you do a compression test on any engine when it's cold it will be low. Especially when you have forged pistons (they expand as heat rises), that is why the piston-wall clearance is so high. Warm the engine up, and then try it again you will have higher numbers. Also do a leak down test and you will be able to see exactly where your problem is.
 

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warm ur engine theres a reason the first step in a compression test is to make sure your engine is to operating temperature.

Metal does not keep the same properties at different temperatures
 

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warm ur engine theres a reason the first step in a compression test is to make sure your engine is to operating temperature.

Metal does not keep the same properties at different temperatures
Yes, that is why your wet compression tests were so much higher (they were sealing the gaps in metal). As metal heats up it expands.
 

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Classic Man
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i can make my D17 create over 280psi if i keep cranking it... thats not how a compression test is supposed to be done.

after 4 compression strokes i get between 205-210psi across on a warm engine.

compression tests dont mean shit if they arent done right, and even then they dont tell you much.


its time for a leak down.
 

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Usually if the compression test in all cylinders reads high or low in some cases doesn't really matter since all compression testers will read different. What matters is the consistency of the numbers, usually within a 10%-15% difference in compression from the cylinders usually will mean the motors still healthy. It's when the difference exceeds a significant amount is when there is an issue.
 

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Discussion Starter #20
Vitaras on custom length rods.

No smoke at all.

Ring gaps were set at .018 tops and .021 second and staggered correctly.

If I have time tomorrow I will do another test with the engine warm.


Also vacuum gauge flickers violently on cold starts, from around 18-23 in/HG. It stops after a few seconds but will do it revving too. I didn't notice it until I put the solid mount in though so I figured it was just vibrating maybe not.
 
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