Author Topic: Compression test, misc ?  (Read 2726 times)

Offline SuburbanHunter

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Compression test, misc ?
« on: March 13, 2015, 03:38:01 pm »
finally back to working on the rust bucket. (77 "Heavy Half" K10). I have questions... some really elementary questions.... but it has been nearly 30 years since I have done any serious wrenching.

I have the "new" engine on a stand "ready" to go in.

I pulled the value covers off and it was very clean. It turns over by hand very smoothly. I haven't pulled the oil pan off yet but probably will.

Thought I should do a compression test. Can I do that turning it over manually or do you have to crank it? Would the PSI be less cranked by hand? Is this a waste of time? 

My plan is to
1) put the 'new' motor on the floor.
2) Drive the truck in.
3) Pull out old motor and put it on the stand.
4) Pull off all the stuff I am going to reuse; Flex plate, hoses, brackets, oil filter adapter, etc

So now I want to clean up the engine compartment without creating an EPA Super Fund site on my property. I'd like to be able to contain and depose of the gunk that comes off/out. I am not going for show truck here I just want a relatively clean, cosmetically not terrible engine compartment to work in. So how do I contain the mess? I will drag it out of the garage for that. Been thinking about getting a big shallow pan and lining it with newspaper of wood chips. Then spray with degreaser and scrape/brush? Seems like if I used a pressure washer or hose I'd get a huge mess. Ideas and experience appreciated.

5) Put the 'new' motor on the stand bolt all the stuff to it.

So, I have a Qjet on the 'old' motor that works in this truck with the 'old' motor. I also have a Qjet on the 'new' motor that probably worked fine with the 'new' motor. Which would you use? Would you leave it alone or rebuild it? I haven't ever rebuilt or tuned a 4 barrel carb. I watch several uTube videos and it doesn't look too hard. I can't afford a rebuilt one. So rebuild one (which one?) or one it as is? I will eventually rebuild the one I don't use to learn how.

steps 6 through 1,999) drop the 'new' motor in, start it up and drive away into the sunset.

I know ya'll are thinking "this guy is Never going to get that truck on the road again" but you would be wrong. It may however be an epic adventure. I'll be asking lots of questions.

Thanks!

Offline SuburbanHunter

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Re: Compression test, misc ?
« Reply #1 on: March 13, 2015, 04:11:08 pm »
should I do a leak down test instead? I don't have a compression gauge or a leak down tester. So I could go either way.

Offline zieg85

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    • 73-87 GM squarebody extended cab and conversions up to 91 R/V series
Re: Compression test, misc ?
« Reply #2 on: March 13, 2015, 06:12:20 pm »
4 mil clear plastic.  Lay it out, tape it down and drive over it. Clean all the dirt grease and junk off, roll the truck back, roll up and toss out.
Carl 
1985 C20 Scottsdale 7.4L 4 speed 3.21
1986 C10 under construction
https://www.facebook.com/groups/248658382003506/

Offline VileZambonie

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Re: Compression test, misc ?
« Reply #3 on: March 13, 2015, 06:17:34 pm »
Why do you need to do a compression test and leakdown test on a "new" engine?
,                           ___ 
                         /  _ _ _\_
              ⌠ŻŻŻŻŻ'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10

Offline SuburbanHunter

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Re: Compression test, misc ?
« Reply #4 on: March 13, 2015, 06:32:52 pm »
Sorry, I was being sarcastic with the "new". It is just new to me. Came out of an RV, a Goodwrench 350 replacement, supposed to have low miles  and was allegedly running when removed. 

Offline enaberif

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Re: Compression test, misc ?
« Reply #5 on: March 13, 2015, 06:51:24 pm »
Just do a compression test and see what the numbers yield. Look under the valve covers and spark plugs and that will tell you a lot with what the motor was doing.

Offline VileZambonie

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Re: Compression test, misc ?
« Reply #6 on: March 13, 2015, 07:09:43 pm »
You need a consistent cranking RPM to check compression. Hook up a starter, battery and charger. Use a remote to crank the engine
,                           ___ 
                         /  _ _ _\_
              ⌠ŻŻŻŻŻ'   [☼===☼]
              `()_);-;()_)--o--)_)

74 GMC, 75 K5, 84 GMC, 85 K20, 86 k20, 79 K10