5 main engine oiling issues

[rick charles]

Having built a couple of 1725 engines over the years,and reading statements on the old forum,I know that there have been complaints about bearing failure usually associated with insufficient oiling. Has anyone really investigated this? I know from experience that the capacity of the holbourne-eaton oil pump is about equal to that of a pump for a sprite/midget.The 1725 has an enormous amount of bearing area. Was there ever such a thing as a high capacity pump? Comments? Rick

 

[64beam]

Hi Rick,

Talking to some people who have rebuilt 1725's, if in worked form definately require high volume oil pumps but in standard form the normal pump should be fine. In regards to what pump they have used, hopefully someone who has built one can advise you.

Regards, Robin.

 

[RootesRacer]

Having built a couple of 1725 engines over the years,and reading statements on the old forum,I know that there have been complaints about bearing failure usually associated with insufficient oiling. Has anyone really investigated this? I know from experience that the capacity of the holbourne-eaton oil pump is about equal to that of a pump for a sprite/midget.The 1725 has an enormous amount of bearing area. Was there ever such a thing as a high capacity pump? Comments? Rick

The sprite midget pump is MUCH lower capacity than the 1725 pump.

For a properly built engine with good bearing clearances, the stock pump is sufficient. As the clearances get very loose, the LOP problem arises, and you get 10psi hot idle.

For a hotter engine build or when higher bearing cooling flow is planned, the 1725 pump innards can be swapped for a 5 main MGB gerotor set.
This yields 22% more flow, but is not a procedure most folks can perform, since it requires critical machining operations (lathe and welding).

The extra 22% is not needed for a normal engine, and unless the engine is setup to use the added capacity (looser clearances and squirt slots on the rod journals) the extra capacity is wasted by the relief valve, and the oil is worked harder than it would have been had the oil not been bypassed.

 

[sunbeam74]

In the old, 1960's, race engines I have taken apart none have had a pump different than stock. However, the pump clearance has been tightened up.

After seeing a number of Alpines that were raced in the 60's clearly oil temperature was a concern based on some of the approaches to add additional oil coolers and in one case extra capacity. Of course, higher temperatures the lower the pressure.



Steve

 

[rick charles]

oiling issues

Here's what I am doing: Using the guts from a TR6 oil pump. The gearorotor is 1.625 inches long. The stock alpine pump rotor is 1.125". External dimensions are the same. Using some alloy tooling plate machining a spacre for the additional rotor length, doweled for location. Welding up the end plate casting then boring a blind hole to allow the pump shaft to protrude through the rotor thus supporting the rotor at both ends. Every old pump I have taken apart has tapered wear in the housing, measured with a bore gauge. Shorten the pickup, lenghten the feed pipe. Fab a new shaft,harden, quench and temper. I did consider machining a new housing but don't think its necessary. I'll be the first to admit that this is beyond most folks, but there are certain advantages to having a machine shop. More on this later. Rick

 

[RootesRacer]

Here's what I am doing: Using the guts from a TR6 oil pump. The gearorotor is 1.625 inches long. The stock alpine pump rotor is 1.125". External dimensions are the same. Using some alloy tooling plate machining a spacre for the additional rotor length, doweled for location. Welding up the end plate casting then boring a blind hole to allow the pump shaft to protrude through the rotor thus supporting the rotor at both ends. Every old pump I have taken apart has tapered wear in the housing, measured with a bore gauge. Shorten the pickup, lenghten the feed pipe. Fab a new shaft,harden, quench and temper. I did consider machining a new housing but don't think its necessary. I'll be the first to admit that this is beyond most folks, but there are certain advantages to having a machine shop. More on this later. Rick

Same procedure as the MGB gerotor set, which is 1.375".

OK, so the TR6 is taller yet, what are you going to do with the extra capacity?

Stock motor cant use it without dumping it out the relief valve, and the extra volume of oil imparts more force on the cam/pump gears at a given oil pressure.