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GMC V6 and V12 Engines Engine repair and rebuilding

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  #1  
Old June 20th, 2019, 06:57 PM
Butter Butter is offline
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Default Engine mount bolts

Hello

I知 installing a 305c into my 1966 1 ton dually. I知 missing all the bolts for the bell housing and engine mounts. Anyone know what size they are?

Also, I知 going to install the sm420 trans onto the engine first then install into the truck. I知 new to this so any pointers would be greatly appreciated. I知 worried about getting the clutch fork and throw out bearing fitted properly. I purchased the truck with no engine have been trying to piece everything together.

Thanks!
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  #2  
Old June 20th, 2019, 08:46 PM
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AZKen AZKen is offline
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Default Re: Engine mount bolts

In general, if you don't know the size of bolts, you measure the thread diameter of the threaded hole or the clearance hole. Old trucks just used a few fractional sizes and mostly coarse threads. Read up on thread sizes and get some calipers and a thread gauge. The type of work you are doing makes you a genuine mechanic, not a tinker-dinker. So get some of the tools I mention and learn screw/bolt sizes. The lengths are determined by how much length it takes to go thru (or into) all the parts, including washers and nuts. If there are blind threaded holes, stick a screw driver in there are see how deep it is. Then back off some. The area you are in now will be 5/16-18 , 3/8-16, 1/2-13. Maybe 7/16-14. This is basic stuff you need to be able to figure out. It is not necessary to ask and wait for that info. You can always try a bolt in a hole and see if it threads in, then take it to the store to get a correct length and etc.

It's good to clean out (chase) the threads gently with the correct tap ,and oil, if they are old, dirty, rusty. Clean gunk off threads with brake cleaner or carb cleaner or soap and water. Nice to have a good tap and die set which will include that thread gauge. Find a set with hex dies not round.

It is great to ask all about your truck and how to do this and that. We will help you do anything. Not talking down to you, just teaching you that hardware is hardware. It's THE basic part of "mechanican", if that's a word. You have all the parts, just look at them and measure the holes. Clearance holes are the one's with no threads that the bolt goes thru. The correct bolt will be the nearest fraction less than the hole size....to leave a little "clearance" for movement and tolerance buildup. This will be confirmed by the threads it goes into.

Be sure there are no cross members or obstacles that will prevent installing motor and trans together. If not, it's a good idea to attach together.

The fork is "clipped" to the bell housing and loosely holds the throwout. You will have to have the motor stationary and the tranny slung or sliding onto the motor. You will have to fiddle and diddle the trans shaft and throw out to gently insert shaft into, and thru, the throw out and into clutch spline. Rotate trans shaft by turning rear yoke as you enter, to mate splines. The throw out bearing may fall out and have to start over. The key is having those two big things oriented to be able to slide tranny without much effort. On the floor/floor jack or hanging on chains.
I assume you know you need to align clutch with a tool as you install it to flywheel.

Last edited by AZKen; June 20th, 2019 at 09:45 PM.
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  #3  
Old June 21st, 2019, 04:15 AM
Butter Butter is offline
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Default Re: Engine mount bolts

Thank you for your detailed response, that all makes a lot of sense. Your help is very much appreciated.

Today I ran into another problem.

I bought a 305e for parts because I am missing so many things for my 305c. Mainly the bell housing to mate the transmission. The bell housing has bolts on the lower bottom inside corners that I can稚 get to unless I pull the clutch and pressure plate?

The engine I知 going to use has the clutch and plate already on so I figured it would be easy swap but I知 scratching my head as to why they would design it like that. Perhaps I知 missing something.
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Old June 21st, 2019, 06:12 AM
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AZKen AZKen is offline
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Default Re: Engine mount bolts

Yes drop clutch, pressure plate AND flywheel.

Last edited by AZKen; June 21st, 2019 at 06:20 AM.
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  #5  
Old June 21st, 2019, 02:48 PM
James James is offline
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Default Re: Engine mount bolts

I might be wrong but our GMC engine started it life as a semi-truck engine and it only accept a SAE bell housing, and not like a regular pickup/car engine.
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Old June 21st, 2019, 06:26 PM
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Default Re: Engine mount bolts

My Donor engine is frozen, can I get to the bolts without being able to turn the flywheel?
(Regarding dropping the clutch, pressure plate and flywheel)
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Old June 21st, 2019, 07:13 PM
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Default Re: Engine mount bolts

It would be kind of rare for it to be frozen permanently. I highly doubt it unless a major event happened. Better double check that. Take out all plugs. Are these motors at the same place as you? If so, you will have to try to get bolts out. Probably will be almost impossible. Maybe thru various access holes and using ujoint sockets. But I don't think the motor is permanently frozen. There are methods of gradually letting pistons soak and etc. You don't say if the motor is in or out of a truck. You don't say why you think it's frozen. Lot's of unknowns on my end to be able to advise. Seems like info is being trickled out. Seems odd you would ask about getting at the bolts if you had the motor right there? It must be miles away.

Last edited by AZKen; June 21st, 2019 at 07:22 PM.
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  #8  
Old June 21st, 2019, 09:23 PM
Butter Butter is offline
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Default Re: Engine mount bolts

AZken- both motors are out of the truck sitting next to each other. The person I got the donor engine said it was frozen due to a stuck piston ring. When I grab the flywheel it definitely won稚 move. On the engine I知 goin to instal it moves very easy but my dad and are we池e thinking the same thing. Probably a way to get it unfrozen. The truck is at my shop without internet so I知 always asking questions when I get home.

My truck came without an engine. It originally has a 351 but I purchased a (good running) 305c and the frozen donor is a 305e. The 305c came out of a bigger truck probably 3500. So it has a different clutch, water pump bell housing and other minor changes as I知 sure your aware of. I also have to put a stud in the side of the engine like the 305e has to instal the motor mount. Looks like I値l work on getting the donor unstuck so I can use that bell housing.
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Old June 22nd, 2019, 12:01 AM
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Default Re: Engine mount bolts

OK sounds good. Post a picture of the "stud" so I can see what you are talking about.

I don't remember a stud.

Actually, I don't know anything about the "differences" you mention. 10" vs 12" clutch?

If you soak it thru the plug holes, it will break loose. Rock the crankshaft back and forth after soak. I guess you are not worried about breaking anything in the motor. So no danger there. Maybe some MMO and Kroil......or equivalent.

Last edited by AZKen; June 22nd, 2019 at 12:09 AM.
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  #10  
Old June 22nd, 2019, 01:23 AM
bigblockv6 bigblockv6 is offline
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Default Re: Engine mount bolts

I also have to put a stud in the side of the engine like the 305e has to instal the motor mount. Looks like I値l work on getting the donor unstuck so I can use that bell housing.[/QUOTE]

What I have done to place that stud in is remove the threaded plug and simply drill it and tap it and thread in a stud the mig weld it so it's permanent. Built one for my 478M conversion and one for a former member of the site
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