Mopar Big Block High Volume Oil Pump Bolt Size

[AndyOpi66]

Hi all,

I have seen this topic come up a few times, without anyone actually answering it. Like most I don't like to spend money on expensive fasteners for basic things, like for example the oil pump bolts.

Most people know when going to the high volume pump on a Mopar Big Block you need longer bolts, as the factory ones are no longer long enough due to the additional 1/4 in length of the rotor and housing. However, the length of new bolts needed is never discussed. ARP and others do sell bolt kits but they are often double the price of the standard grade 8 bolts you can get at you local hardware store.

For this reason I made the following video, that discusses the size difference between the factory pump and a high volume and also lets you know the size of bolts needed. Hope this helps some of you out!



For those of you having trouble with the video the bolts needed are (3) 3/8 by 3 and (1) 3/8 by 4.5.

 

[gkent]

Well if the pump is 1/4" thicker doesn't it just make sense that the bolts should be 1/4" longer ?!?!?!

 

[AndyOpi66]

Some people don't have the original bolts for reference.

And the original bolts sizes are also hard to find. You can do a search and find this as well. Also, I had to do some research and measure the rotor sizes to double check the findings the pump was a 1/4 in longer, I didn't want to just take someone's word for it. Hence the video, so others wouldn't have to do the same work.

 

[Kern Dog]

Thanks, Opie.
Information sharing helps everyone. Sometimes we state what seems obvious to some but is helpful to others.
I knew the high volume pumps were thicker, some members here may not have known.
Cheers.

 

[451Mopar]

I usually have to trim down the three 3" bolts so they don't bottom out in the block holes.

 

[AndyOpi66]

I usually have to trim down the three 3" bolts so they don't bottom out in the block holes.

Thank you for pointing that out. With a standard pump this would more than likely be needed, but I did not have that issue with a high volume on my 383. The original shorter bolts for the standard pump were about 2.75in long, so this would make sense for that application.

 

[Daves69]

Some more info for WIW.
DC use to sell a long pump rotor and plate kit. It came with 3" bolts and the 4-1/2". Those 3" were too long as well.

Interestingly, I recently purchased a HV pump from Mancini along with their recommended bolt set for the HV pump.
I received one 4-1/2" bolt and three 2-1/2" bolts which are too short. Believing they sent a standard pump set I called them and they claimed their bolt kit came as 2-1/2" and the 4-1/2". Live and learned there.

 

[451Mopar]

Some more info for WIW.
DC use to sell a long pump rotor and plate kit. It came with 3" bolts and the 4-1/2". Those 3" were too long as well.

View attachment 1539457
View attachment 1539462

Interestingly, I recently purchased a HV pump from Mancini along with their recommended bolt set for the HV pump.
I received one 4-1/2" bolt and three 2-1/2" bolts which are too short. Believing they sent a standard pump set I called them and they claimed their bolt kit came as 2-1/2" and the 4-1/2". Live and learned there.
View attachment 1539469

I see the double washers on those 3" bolts
I always trial fit the bolts without the washers. If the bolt bottoms out you can see/measure how much it should be shortened, or how thick of a washer you will need.

 

[Daves69]

Lol, I still have that pump as you see it. A swap deal came about way back where I didn't need to use it.

I always trial fit the bolts without the washers.......

I use the "1 to 1-1/2 X the bolt diameter" for thread depth engagement.