Camshaft bearings

[Henry Harris]

I'm going to restrict the flow of oil to the camshaft bearings of two engines that I'm working on.

What are the suggested new diameters of oil feed holes for pressure fed, and for jet fed too? (I'll be fitting 'O' rings)

Thanks

[Howard Wright]

Hi Henry

I use 1/8” holes for the jet fed engines I’ve built. 

Cheers

Howard

[Terrytuned]

Henry 1.5mm 1/16" for pressure fed and 3/32" 2.5mm for splash, I use a restrictor in the side oil feed gallery. Terry.

[JonE]

can the restrictor be done without machining? Presumably one wants to be able to de-restrict when the gallery wants cleaning occasionally.

[dickie65]

Hi Jon,
The restrictor is used on pressure fed engines to force more oil into the crankshaft.
You can tap the gallery and scew a plug with a suitable hole to slow the flow down.
( I have just got a drilled brass plug knocked into place )
O rings are fitted to the outside of the front bearing to stop oil passing around the outside of the bush.
I have couple of front bushes from a standard engine that have track marks from oil scouring the bush and crankcase.

If you are running a standard engine there is plenty of oil flow for everything at normal speeds.

I run my engine at 6500 rpm and more in third gear when pushing on.
My cold oil pressure is set at 70 psi at 1000 RPM, hot oil pressure at 1000 RPM is 28 psi.

[Bob Culver]

The oil track erosion marks are typical (and surprising). I used to just build up with solder around the feed drilling. Not to be overdone as do not want shavings of solder floating about.

[Speedex750]

Hi Henry,

This is a vital mod for the three bearing engine to push as much oil as possible towards the centre main bearing. The rear cam bearing of any A7 engine doesn't need restricting as the small running clearance between the bearing journal and bush forms a limiting restriction. The front cam bearing isn't as simple as the groove down the bush can dissipate oil. However, the splash of oil out of the front of the bush is what forms most of the lubrication for the timing gears so you have to retain some release. I've no experience of pressure fed engines but I use a drilling of 1.5mm for the front bearing of my three bearing splash engines. I drill and tap the oil feed hole of the bush and insert a brass screw with the 1.5mm drilling - looking very similar to a Zenith jet. The centre cam bearing can be blanked, an undrilled bearing shell effectively achieves this and it can be lubricated by a drain drilled from the tappet chest above it, a 3/16" drilling seems to give enough lubrication. The O ring mod is also a good one to make for any engine. 

I hope that helps, Dave

[Terrytuned]

Tap through the 1/8bsp blank plug into the gallery deep enough to take a socket drive blank plug drilled the required size    

[Mark Dymond]

"The front cam bearing isn't as simple as the groove down the bush can dissipate oil"

My front camshaft bearing has no "grove" - potentially home made. can someone post a photo of a front bearing showing the groove and proper shape.

[Bob Culver]

Hopefully did not run with one of the  alternator replacemets and the diabolical gears supplied..... The oil trench is mentioned in very few sources and only the most observant likely to realise its full function. I have seen cars with an auxillary feed to the cover on the dynamo support casting, but with the groove functioning this would seem pointless.