Thread: low compression

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have a 402 in a 72 gmc truck. cyl 8 and 5 have 30lbs. since I want to sell this truck after painting and interior is done, can I do a ring kit only? do I have to pull motor or can drop pan and pull heads? I would fully disclose what has or not been done to motor but would like it to run decent to sell. if not can sell as a mechanics special. any other recommendations for engine repair welcome.

You just came close to giving a couple of the folk here mental duress.

Anyway, the problem could be valves or rings or both. Could have worn cam also. The only quality repair is a full rebuild. That being said, dropping the rotating assembly from the bottom is a royal pain, and re- ringing without a bore is sloppy work.

BUT. If you mike the cylinders, and they are nominally free of taper or oval, then you can cut the ridge, hone, and have a reasonable repair. No way to do that without pulling heads, so you may as well lap the valves. It's cheap and easy.

thanks for reply. I do not want to do any sloppy work. I did a leakdown test on #8 only and had air coming fron dip stick. I assume the worse and will pull the motor remove heads and rebuild. possible I will just sell it as is and let a full time mechanic go for it.
I posted another possibility on a diff forum and had no reply as of yet. maybe u can comment:
I have access to a 94 motor home = on a chevy 1 ton chassis with a 454 7.4L V8 OHV 16V with 43,000 miles on it. hasn't been run for several years. can I pull that 454 with tranny out of motor home and put in 72 3/4 ton GMC/ what about the computer? how can I do it without the computer and what actually does the computer control on motor? Is this a practical solution or am I causing more mental duress! thanks

If the '94 hasn't run for several years how confident are you that it's good? 43K in a motor home can be rough duty, depending on the driver and terrain. The ECU would have controlled injection and spark, and maybe the transmission. To eliminate you'd need a new intake, carb & air cleaner for sure, and if the tranny is electronic then you'd likely be looking at a stand alone tranny controller, too. Could be a practical solution, if it's a good engine & tranny, and hasn't suffered in storage.

If your not wanting to put a lot of money in the whole kit & caboodle consider parting the whole thing out, good chance you will make more than trying to paint it, rebuild the engine etc, a rebuildable core big block by itself is desireable and so is the year of truck, just a thought as I did it on a '70 Chevy PU and made way more than a rebuilt and I let everyone pick there own parts off in a storage unit 25 years ago (If its a auto trans it will be a very desirable th400 also) Good luck

thanks Matthyj.
Here's my situation- I owned a restoration shop for years doing only high jobs. Paint jobs started at $5,000.00 10 years ago with bodywork additional. not unusual to have projects over $75K in shop. I can do the bodywork and Paint. I like to do it. So actually I can paint this truck and put a paint job on it worth an easy 7-8K with little effort. When they are done it is absolutely show quality. Having said that, I have had much success in doing projects with awesome paint jobs and really nice interiors for years. I do not usually get into mechanical work except tune ups and little things. don't do any frame offs anymore either. I have found that when I do the paint and interior the way I do, when it is for sale and someone drives up, usually the first one buys it. don't know what it is but have never had any trouble selling a beautiful vehicle that runs like crap. seems to me there are more guys willing to do the mechanical than there are really good bodymen and painters out there.
for this project, I was thinking of doing the engine swap since I can have the motor and trans for free. this motor home it is in has no title but everything works in it and I have the maintenance records.
so how can I tell what tranny is in my 72 gmc? it is auto on the column. leaks like a stuck pig.
also on the motor home tranny, if it has a wiring harness to it, I assume it is controlled by computer, correct?
hope I didn't bore you with stuff but would like to have all info before making a decision. I know its a lot of labor to pull the 454 out but actually that's the only extra work to do since my other option is to sell it with bad motor or pull it out, rebuild it and put it back in! I think I am nuts sometimes.
thanks