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Discussion Starter #1
Gents,

we were talking about doing a compression check a while back & you guys had mentioned that the "fist hit" was the one to look for. I did a Comp check this weekend on my BBC & found that this "first hit" thing is VERY UN-repeatable. if the slug is almost all the way to the top on the compression stroke when it "hits", you get a very low number compared to when its coming all the way around & gets a good hit.

The question is............................. whats the point of doing a test if you dont get repeatable results?

I would do a leak down on it, but................. these cheap headers I have wont let me get the gauge in on #8 w/o dropping the headers off the car. I dont really care that much.



Bob
 

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Discussion Starter #2
what 30 folks look but no-body has an opinion? does nobody do a Comp check on thier motors? is that old school?


Bob
 

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Bob,

If you can fit a fittin in there for a compression check you should be able to use the same fitting for the leak down gauge..... ????
 

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Discussion Starter #4
I cant. I have to hand start the plug & then slide a socket over it then put a wrench on the socket to get it snug. Even then if I use a plug socket with the rubber bootie in it, it wont go on the plug.

Bob
 

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Me personally i don't do the first hit deal because of what you have found with your testing.... if i figure the dynamic compression and cylinder PSI for new engines it will take on a average 3 hits per cylinder to get the numbers... this is on fresh brand new engines that i have run on my test stand....

I missed the orginal problem discussion,,, what are you looking for????

Keith
 

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Discussion Starter #6
k-star said:
I missed the orginal problem discussion,,, what are you looking for????

Keith
Keith,

here is the short version. The last time I took the car out it ran well (6.41 back to back in fairly good air). I was real happy with it, however, it had a BAD off idle stumble. I have my WBO2 setup going now & figure out that it was going WAY lean @ tip in. so after talking with my carb resource guy, ( :wink: ) I went down on my idle bleeds & that made it a LOT better (but not real bitchen).

when I took it back up there last time (the night race). it started this smoking thing, which is has NEVER done. & the "only" thing I did was to change the rockers (same ratio) & to put the stud girdle on it. the plugs were BITCHEN the last time I had it out, but this time they were REAL dark & this smoking thing started up. I checked the data logger & it was running quite fat so we pulled some jet out of it. I made another run & it was again smoking this time a bit worse.

we went back to the pits, & ran the valves on it thinking I had one come loose or miss adjusted one or more of them or SOMETHING. It was dark & eliminations was coming up so we went to the lanes hoping to get a bye & make another motor run. I came up against that rustang & I had no idea what he was running so I figured we would run it out on the bottle & just see what happened. dispite air that was >4000' DA, it yanked the front wheels (hard to see in the video, wrong lane :^( & ran out to a 6.50 which was OK to me considering the air. its hard to see in the video, but once it gets to 1/2 track you can kind of see the smoke.

Here is the hard part................. you can not tell from the video or from actually being there where the smoke is coming from or if its black or blue. I assumed it was blue, but after yanking the plugs the other night................... it might be fuel.

when I looked @ the carb the other night I saw fuel on the base of the carb which lead me to take it off of the car & that is when I found the lose screws on the base of the carb. 2 of the 6 screws were only "kind of loose", 4 of them were >1/2 a turn loose. IMO, it was WAY loose for carb base screws. if they took 1/16th turn or 1/32 turn, whatever, but .................

Sorry for the book, thanks for listening & the help.

Bob
 

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I can't play the vid's(my works internet settings)

By any chance are you have any problems with the valve cover bolts getting loose also?????

The only reason i asked is i though it was odd that the carb base plate screws were that loose...plus it's smoking,,, And i know if the engine is detonating it will loosen the valve cover bolts, and i thought maybe the base plate screws also... Just something to look at, not saying thats what is going on here...

So what did you get with you compression readings?????

Also you can leak the other 7 cylinders and let the #8 go for now untill you see a issue with the engine...

Keith
 

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Discussion Starter #9
I cant find the sticky that it was on, but they were all right about 180/190. nothing looked really odd.

I suppose it could be detonating, however, I kind of dont think so. there is no sign of it on any of the plugs. I have not re-checked the timing, but I will do that the next time I fire it up, just to be sure nothing has moved. I have spent quite a bit of time checking plugs on the car the last few months trying to get a good feel for getting a hold of the tuneup & I did not let the bottle loose on it until I was happy with how it was running on the motor. I tried timing changes, jetting changes, etc, to see what affects it had on the MPH, ET & plugs. it all looked good. then I let lit the wick on it & it ran well. This trick came out of nowhere, I would really like to send it back where it came from. LOL

thanks again
Bob
 

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Bob I also recieved variances on"1st Hit" a difference of 10-20psi of course i didnt likewut i saw and eventually did the leak down test.
originally when I did the compression test with three full revolutions it was no more than 5psi across the board the leak test confirmed the orignal comp test. Monty suggestd the "1st HIT" results and I just couldnt get the stability i was looking for doing it that ways maybe i went about it the wrong way
 

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The *First Hit* method is not accurate and is never repeatable UNLESS you take the time to put the engine in the EXACT same position BEFORE you start the test.

Do (5) hits on the guage. I prefer the spark plugs out.

If all 8 cylinders are within 10 to 15 psi, then a leak down is pointless.

I have put different rockers on an engine. This was done on an engine stand to check different rocker arm manufacturers for geometry issues. The results were incredible, anyways.......FWIW before you get excited, they were all the same ratio as well. If this was the ONLY true change (rocker arms) on YOUR engine, then I would be looking into valve guides.

There's my 2 cents. Ok, I'm broke now.
 
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