Alex. A New Member 8 Member For: 4y 8m 11d Gender: Male Location: Brisbane Posted 02/04/20 05:09 AM Share Posted 02/04/20 05:09 AM Hey guys, Long-time lurker first time poster.. I'm rebuilding my fg xr6 turbo atm.. just curious as what other ppl and sending their main and big end clearances at? I have the factory specifications which are super tight compared to what I send motors at usually. Any info would be fantastic. Thanks guys Link to comment Share on other sites More sharing options...
k31th less WHY; more WOT Site Developer 28,991 Member For: 16y 7m 13d Gender: Male Location: Melbourne Posted 02/04/20 08:01 AM Share Posted 02/04/20 08:01 AM just go with whatever the parts manufacturer chose as clearances and if they say the factory ones, go with those. 1 Link to comment Share on other sites More sharing options...
Alex. A New Member 8 Member For: 4y 8m 11d Gender: Male Location: Brisbane Posted 02/04/20 11:06 AM Author Share Posted 02/04/20 11:06 AM (edited) 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. Edited 02/04/20 11:09 AM by Alex. A Link to comment Share on other sites More sharing options...
NA_TURBO Member 532 Member For: 9y 1m 15d Gender: Male Location: Mildura Posted 02/04/20 11:13 AM Share Posted 02/04/20 11:13 AM Hi, just curious what was your hot idle oil pressure?I have a built motor and on cold it rattles and once hot its quiet but has low oil pressure, but not low enough to activate the warning light. Link to comment Share on other sites More sharing options...
gaz097 Bronze Donating Members 1,751 Member For: 13y 4m 2d Posted 03/04/20 01:32 AM Share Posted 03/04/20 01:32 AM No one here is really going to be able to help you. I have messaged Tony berlett (tbre) engines before through Facebook and he was somewhat helpful. Give that a try. Or even give Brad from atomic a call. He is good over the phone. If you have bought parts through him he is pretty helpful. When I built my engine I followed the Gregory manual, but it appears to have the same spec as what your listing. I never machined my crank or anything cause tight ass, but I did fit thou undersized mains which put me bang on bottom tolerance, which has been fine to this day. (I don't have a oil pressure gauge or have any validation to this) it was definitely tight though, and gave my old man some pain as he thought the specs were way to tight as well. I went standard size bearings on the rod, which put me on the top side of spec, but below allowable. Gregory manual. It doesn't list a difference between na and turbo, and the cranks are all the same from factory. So tolerances must be the same. 1 Link to comment Share on other sites More sharing options...
gaz097 Bronze Donating Members 1,751 Member For: 13y 4m 2d Posted 03/04/20 02:34 AM Share Posted 03/04/20 02:34 AM It is interesting and you may be able to enlighten me, but you can buy thou oversize ACL bearings from the website for stock size. Is this something you would use if you bought a brand new crank and we're planning to race/push hard? Link to comment Share on other sites More sharing options...
Alex. A New Member 8 Member For: 4y 8m 11d Gender: Male Location: Brisbane Posted 03/04/20 06:40 AM Author Share Posted 03/04/20 06:40 AM Correct mate and you can buy .001" undersized also. This is just so you can tailor your clearances so suit the specific use and clearance required. Some cranks vary a few tenths as do main tunnels and rod bores.. with stack tolerances you can end up quite far away from the desired clearance.. which is then when you mix and match std and hx bearing shells to get the clearamce wanted. Its also interesting how much different manufacturers bearings change in clearance.. we generally find acl is on average .0005" looser then clevite for the same part bearings.. Looks like I might just try dropping the clearance down and see how it goes. 19 hours ago, NA_TURBO said: Hi, just curious what was your hot idle oil pressure? I have a built motor and on cold it rattles and once hot its quiet but has low oil pressure, but not low enough to activate the warning light. My hot pressure was 15psi to 19psi roughly and 750rpm.. not horrible bit compared to the 30psi minimum it had before with worn out std bearings I was just a bit suprised. Link to comment Share on other sites More sharing options...
finnas Gold Donating Members 105 Member For: 14y 10m 11d Posted 03/04/20 08:49 AM Share Posted 03/04/20 08:49 AM 2 hours ago, Alex. A said: My hot pressure was 15psi to 19psi roughly and 750rpm.. Sounds normal to me. 40psi @ 1500-2000 60-75psi higher in the revs Link to comment Share on other sites More sharing options...
Alex. A New Member 8 Member For: 4y 8m 11d Gender: Male Location: Brisbane Posted 03/04/20 11:16 PM Author Share Posted 03/04/20 11:16 PM Although this is within oem spec, its lower then I would like to see in a brand new motor running a 15w40 oil.. considering it was over 30pis hot with thinner oil before the rebuild... Link to comment Share on other sites More sharing options...
SamFG New Member 3 Member For: 4y 7m 13d Posted 09/04/21 07:18 AM Share Posted 09/04/21 07:18 AM Hey Alex What bearing clearances did you end up using and hows your oil pressure now? Also did you do any modifications to your oil pump? Thanks Link to comment Share on other sites More sharing options...
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