C1 Oil Pump question

[Joe L.]

Re: C1 Oil Pump question

My engine on my 1960 was rebuilt 9 years ago and ever since that time, at cruising speed, the oil pressure gauge stays at 60 psi. At idle, it drops. My mechanic informed me that he did not install a high volume pump (I did not ask what type of pump he installed). I suppose the gauge could be incorrect. I have wondered about the high reading for 9 years, but the engine is working just fine; so I guess there is no reason to be alarmed.

Joe-----


He may not have installed a high volume pump but he may have installed a high pressure pump. The only difference between a standard pressure and high pressure pump is the installed pressure relief spring.

[Joe M.]

Re: C1 Oil Pump question

Thanks Joe, that is a good point. I will bring that up next time I am in his shop. Since the apparent high pressure condition has existed for 8 years after rebuild, any reason to be concerned? There should be a way to connect an accurate pressure gauge on the end of the oil pressure steel line and measure the pressure to determine if the high reading is real or a faulty gauge; or do nothing if it isn't a big deal.

[Clem Z.]

Re: C1 Oil Pump question

Thanks Joe, that is a good point. I will bring that up next time I am in his shop. Since the apparent high pressure condition has existed for 8 years after rebuild, any reason to be concerned? There should be a way to connect an accurate pressure gauge on the end of the oil pressure steel line and measure the pressure to determine if the high reading is real or a faulty gauge; or do nothing if it isn't a big deal.

unless the pressure is extremely high like 100# cold i would not worry. a lot more engine have been ruined by low oil pressure vs high pressure

[Duke W.]

Re: C1 Oil Pump question

I think this is the 292nd time I've put in this post.

Ninety percent plus of OE pumps are okay to reuse. It's a very simple task to disassemble the pump an inspect the gears and inside of the housing. If the pump has never ingested debris, chances are it looks virtually new with just "burnishing" on the wear surfaces.

You can "blueprint" it by dressing down one gear and the housing mating surface as required on a piece of glass with some 220-400 paper wetted with mineral spriits to get the end play down to about .002-003" on each gear. Measure it with a machinist's straight edge and feeler gages.

Every "engine builder" wants to just replace the oil pump and usually with a high volume/high pressure pump, which creates nothing but headaches and anxiety when you drive around with the gage pegged all the time, and that will also fail a PV.

Millions of these engines, including all of the mechanical lifter small blocks built up to late '63 were assembled with the standard volume, standard pressure (40-45 psi hot at 2000-up) oil pump that was the same as used on 2-bbl. 283s.

If it works, you don't need to fix it.

Duke

[Gary C.]

Re: C1 Oil Pump question

Domenic,

As Joe points out the 57-8 283 engine blocks are unique and use the Melling M-46. Save your old pump shaft as the Melling IS46 pump shaft is not available.

Gary
....

[Joe L.]

Re: C1 Oil Pump question

Domenic,

As Joe points out the 57-8 283 engine blocks are unique and use the Melling M-46. Save your old pump shaft as the Melling IS46 pump shaft is not available.

Gary
....

Gary------


I believe the IS-46 intermediate shaft is still being manufactured by Melling. However, it's an item that no auto parts store or automotive parts warehouse is going to stock. The only way to get it is directly from Melling and most retail sources don't want to go to that trouble for a low-buck piece like this. I don't know if an individual can order directly from Melling, or not. Sources like Summit Racing will, though.

Also, from what I can determine there were 2 different shafts used over the 1955-E59 period. 1955-57 used shaft GM #3836624 (yes, this is the original part number). This is replaced by the Melling IS-46. 1958-E59 used shaft GM #3739826. This is replaced my the Melling IS-55E.

[Gary C.]

Re: C1 Oil Pump question

Joe,

A couple of years back I spoke with Melling Tech Support and they told me that the IS-46 was no longer being manufactured. Melling could have brought it back since then.

Gary
....

[Joe L.]

Re: C1 Oil Pump question

Joe,

A couple of years back I spoke with Melling Tech Support and they told me that the IS-46 was no longer being manufactured. Melling could have brought it back since then.

Gary
....

Gary-----

I expect they're making them again. I checked further and the Melling web-site shows them as being available. Also, Summit Racing will take an order for them and says the shaft will be shipped directly from the manufacturer.

Now, the question arises as to WHY they would still be making these? Just how many 1955-57 Chevrolet small blocks are still out there running and how many of those need a new intermediate shaft?

[Jim L.]

Re: C1 Oil Pump question

What is physically different about the '55 - '57 pump shafts?

Expiring minds want to know.....

Jim

[Joe L.]

Re: C1 Oil Pump question

What is physically different about the '55 - '57 pump shafts?

Expiring minds want to know.....

Jim

Jim-----


Length is the primary difference. The 55-57 intermediate shaft is about 1" longer than later small blocks.

[Gary C.]

Re: C1 Oil Pump question

Jim,

Joe's correct on the shaft length. And correct that the Melling website now lists the IS-46 shaft.

The IS-46 shaft is 6.83" long. The IS-55E shaft is 5.96" long.

The problem I had was that the M-46 oil pump is shorter than the M-55 by approximately 1/4". Distributor won't seat if a M-55 oil pump is used with the IS-46 shaft and the IS-55E shaft is too short.

Gary
....

[Jim L.]

Re: C1 Oil Pump question

Jim,

Joe's correct on the shaft length. And correct that the Melling website now lists the IS-46 shaft.

The IS-46 shaft is 6.83" long. The IS-55E shaft is 5.96" long.

The problem I had was that the M-46 oil pump is shorter than the M-55 by approximately 1/4". Distributor won't seat if a M-55 oil pump is used with the IS-46 shaft and the IS-55E shaft is too short.

Gary
....

Joe, Gary, thanks for explaining the difference. I stumbled over the different pump/shaft compatibilities 45 years ago but didn't really understand what I was seeing. I've always wondered what went wrong......

Anyway, Gary, the way I'm reading your problem description, it sounds like the height of the rear main bearing caps on the very early small blocks must also be different than on later small blocks.... maybe due to the change from rope seals to neoprene seals? I dunno.

Jim

[Clem Z.]

Re: C1 Oil Pump question

here is the difference