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Puffwagon's Territory Adventures


Puffwagon

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Where did you get 3 thou from?

I know the atomic motors have low oil pressure when hot.

This if from a thread around here...

 

Sowwy.

This

On 02/04/2020 at 10:06 PM, Alex. A said:

Thanks for the reply mate,

 

The aftermarket parts don't really come with a specified bearing clearance as such.. 

Bit of a long winded reply here so excuse if it gets boring haha

 

I build engines for a living at a shop here in Brisbane, however every motor we build has a dry sump set up with an external oil pump so we send the bearings quite loose to survive... I don't build many street motors anymore and this is my first xr6 I have built.

 

The usual rule for bearing clearance is .001" per 1" of journal diameter(add .0005 for extreme boost/no2 applications).. this is accepted pretty generally... 

 

This would put the  barra mains somewhere around The .0025-.0026" and the big ends around the .0021".0022" for a std motor using this Formula.

 

looking at the barra workshop manual, they specify

Min/max clearance for the mains and big ends at .0007"-.0015"... that's insanely tight  for a boosted application With the journal sizes it has!!

 

Is there a different workshop manual for boosted barra motors?

 

I initially built the motor and set the bearings at .0023-.0025" for the mains and the big ends set a little looser at .0025-0026".

 

However once started, the motors hot idle oil pressure was drastically reduced from the Pre rebuild pressures.. I guessed it was due to the extra bearing clearance and the oem oil pump just can't keep up with the extra leaks.

 Cruise pressure seemed acceptable, however idle pressure had halved..

 

So I have torn it back down and will re do my bearings...

 

I was really more curious at to what other barra engines builders are sending their clearances at... 

 

Thanks again guys.

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  • Puff
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  • Member For: 9y 1m 28d
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  • Location: South Australia

Bearing clearance is only part of how much oil pressure a engine makes. Pump specs along with oil properties will vary pressure significantly.

 

I've changed the oil pump specs for this rebuild and as such will be making approx 50% more pressure over stock.

 

I think I'll be fine with what I'm doing and if not I'll swap the mains back to std. It's only $300 for another set of mains so not the end of the world :)

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Not saying your wrong, just curious.
Contingency program is always good.

I remember measuring up my journals and them being just outside of ford allowable. Went thou under bearings on a stock un machined 160k kay old crank.
Tolerances were on the bottom side of stock so super tight but in spec. Didn't have any issues but I never checked the bearings over time.

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  • Puff
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  • Member For: 9y 1m 28d
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Eh I might be wrong but that's ok. It's a thing I want to try so try I will! Haha at least the weather is nice so won't suck too bad to be reyanking the engine or dropping the subframe etc.

 

This is a channel that I follow on youtube and he has some good info there. It's given me more confidence to do what I'm doing with the various parts and intended power output.

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@Nikzadik Hey mate I got the notification on YouTube but the comment is gone.

 

The reason it came on so late in that clip is for a few reasons. One is that it's got a 76mm turbo and the other is it has quite large cams with adjustable gears. Also it was on 98 so you lose a bit there too.

 

Best case with stock cams and that turbo is full boost somewhere between 3500 and 4k rpm. With the large cams set at 00 it'll come on at about 4k.

 

It has rolling anti lag so I can get it spooled earlier if needed.

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  • Member For: 9y 1m 28d
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  • Location: South Australia

The piston crowns received a coating of Cerakote V-136 today. Will have the skirts done tomorrow with their P-109 Micro Slick formula and the short block can be fully assembled. Might get it done over the weekend but I'm coming down with a sore throat and aches etc, so might do fark all for a week :declare:

 

Obligatory pic

 

d6yKqbb.jpg

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