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Old 05-13-2009, 04:06 PM   #1
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Default Compression test results on new engine, help

New rebuilt engine. Fully built engine.

Anyway, I had a track day about 2 weeks ago. car was fine. last 2 runs it had a miss fire while idling. mmmmmm ba ba bammmmmmmba ba bammmmmmmmba ba bammmmmmmm bababa

you get me. While drive full ***** i didnt feel the miss at all.

So I went home and put the car away.
last night I did a comp test just to make sure i didnt have a mechanical or serious type of issue. Maybe just a lose wire or some dumb ****.

Anyway, cyl 123 all at 180. Cyl 4 at 160!!!!!!!!!!!

WTF guys/ I am just looking for ideas of the tops of your heads.
I will be having a leakdown test done by my machinist next week.

i just wanted some of your ideas before I even go to the shop. I am fukken pissed and sad. I dont much a budget left for fixing ****..

I hope its a simple valve issue that will be quick, easy, and cheap to fix..
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Old 05-13-2009, 04:17 PM   #2
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Try a wet test. Small amount of oil into cyl. 1/3 of an egg cup. Crank over with plugs out to blow out excess and recheck comp. If it's a valve issue you'll see next to no diff. If cyl issue the extra oil will have helped seal any blow by and figure will be higher.

Malcolm

To get a better comparison repeat with one of the other cyls.
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Old 05-13-2009, 04:58 PM   #3
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Misfire due to heatsoak? Mine idles like crap usually when very hot - still trying to fix that somehow.

Did you test before the trackday? Maybe just paranoia... I never measured mine after the rebuild and dont care as long as it runs and puts the power down.
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Old 05-13-2009, 06:14 PM   #4
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Quote:
Originally Posted by Spookyfish View Post
dont care as long as it runs and puts the power down.
When I checked my motor, the compression in cylinder 2 was a bit low, 160ish, compared to 1,3,and 4, 180ish, but I concur with Spookyfish!
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Old 05-18-2009, 06:17 PM   #5
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Missed at idle cold, warm, and hot. It didnt do it before my last event though..
Thing is, the comp shouldnt be lower. So thats a problem.. Thats why I need to figure this out.

You guys dont give a **** huh??
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Old 05-18-2009, 07:14 PM   #6
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Try the wet test that malcpw up there suggested to find out if it's a valve, hg, or rings.

How much time is on the motor? Did it overheat at any point during break in?
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Old 05-18-2009, 07:17 PM   #7
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/\

+1 for Ben's response.
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Old 05-18-2009, 07:58 PM   #8
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What is the condition of your oil?
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Old 05-18-2009, 08:24 PM   #9
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Solid lifters?
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Old 05-18-2009, 08:26 PM   #10
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Was the engine warm when you did the test? Throttle held open, no spark plugs in any cylinder?
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Old 05-18-2009, 11:25 PM   #11
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What Alta said ^ IF yes, then pull your cam cover, look at all the valve areas at the cam lobes. IF they look OK, then try rotating the crank by hand slowly while watching (and listening) the action at the lobes.

I had a shim crack on a shim-under-bucket - but all that did was keep the valve from opening all the way. Amazingly the bucket kept all the shim pieces captured instead of letting the bounce around the head. But shim parts could easily hold the valve open and the OE shims are good candidates for cracking or spitting out with the abuse you're giving them.
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Old 05-19-2009, 08:11 PM   #12
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Thanks for all of the replies again guys.
99 head
Engine was cold.
No plugs in any cylinders.
throttle was closed.
oil looked fine, but I am going to check again.
I did not over heat. water and water wetter also looked fine..
The engine has 2 competitions and 1/2 day at a practice event. So not much time
The engine was heat cycled on the dyno. It didnt overheat.

I will look into the comp test with oil this week/end
I will also take off the valve cover to check the lobes and shims
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Old 05-19-2009, 08:50 PM   #13
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Do the test with a warm engine and the throttle open.
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Old 05-20-2009, 10:19 AM   #14
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The first thing you need to do is look at your head up top and make sure you don't have any shims (or pieces) floating around.
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Old 05-20-2009, 10:50 AM   #15
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Check the valve lash adjustment.
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Old 05-20-2009, 01:39 PM   #16
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Quote:
Originally Posted by m2cupcar View Post
The first thing you need to do is look at your head up top and make sure you don't have any shims (or pieces) floating around.
Will do- Before I do anything else.

Quote:
Originally Posted by Alta_Racer View Post
Check the valve lash adjustment.
Thats just shims. I will check them out after I make sure nothing blew apart.
Make sure the lash is still all the same..

Thanks again...
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