Arp rod bolt tension.

So I have a weird little question here regarding ARP rod bolts…

I have a freshly built rb25 with Nissan GTR rods and Ross pistons

standard size ACL bearing have been installed in both rod and mains.

motor has been run and driven for 30km on a dyno but is still unusually tight and lazy.

i am about to pull it down again and see if what’s going on.

my only theory is possibly rod bolt torque might be too tight?

The question is should these be torqued to Nissan specs or ARP specs as they are quite different in ft/lb??

Without diving into it just yet this is all I can think of.

ARP rod bolts should be always torqued as per their manual.

As Shota said - different strength bolts have different torque requirements for the correct stretch/tension.

If there was any sort of bearing issue causing the engine to be a little 'tight', it would have shown itself in a very expensive way already.

You need to get back to basics - the most likely reason for the lack of expected performance is a camshaft, or both, is out a tooth or the camshaft control is playing up.

First thing I'd do is check the plugs and compressions for anything out of the expected as it's an easy thing to do.

Thanks a lot for your input.

engine in about to come out tomorrow and the search begins!

This thing has been on my mind for weeks.

Im guessing I should measure the rod bolts for stretch?

Il post my finding tomorrow.

Thanks again for your advise.

As I said, I'd do the basics first - plug check, compression check, camshaft timing check - which is the most likely culprit if you're sure everything else is correct.

I'd be most surprised if it was a bearing issue, as I'd have expected that to have already shown up as debris in the oil - you have checked? - and possibly a hole in the block.

However, I have been wrong before and sometimes it's worth the work for peace of mind - if you would keep us updated it'd be appreciated.

Ok so I have pulled it all the way down to remove bearings

still no signs for stress?

bearings seem to be in good condition still.

small amount of paste on magnetic sump plug but nothing major

I was trying to avoid pulling the head off at this stage but as an observation the cams seem noticeably dry!

so signs of oil saturation, although the engine has only been operated at 2500-3500 for 30kms.

rod cap orientation has still got me worried though

I marked the everything before I removed them originally but some have the writing facing in two different directions.

photo’s attached

My thoughts, and they may be wrong as sometimes it's hard to judge and I don't know how the engine was assembled.

That looks like insuffient cleaning and a potential oil supply problem. I don't think it's the primary reason for the engine feeling 'tight', but it's fortunate you checked as the bearings were definitely on the way out. What did you use as an assembly lubricant during assembly?

Did you check the oil pickup tube and thoroughly clean it during the rebuild, did it use an "o" ring, or gasket, that could have been same displaced or come lose allowing it to suck air? Was it a new oil pump or a checked original one, and were they checked and primed/packed with grease - worn pumps are also common causes of low oil flow. While you're at it, check the oil pressure relief valve - if it's sticking/stuck the oil will be diverted at lower rpm. On that, did it take a bit to gain oil pressure when initially cranking, and with it running what was the pressure cold and hot at idle and at, say, 3k rpm?

It's normal to have a small amount of fine 'paste' on a magnetic plug - it's ferrous material from ring and bore bedding in, with everything else either protected by an oil film, hopefully there's no other wearing parts, but there are signs*.

Rod caps are fitted with the tangs on the same side - if you got them wrong, or the caps were accidentally swapped, the mis-alignment is usually enough to prevent the engine being rotated during assembly.

*I REALLY don't like the look of the camshafts - photo's can be deceptive, but it looks like they have been getting barely any oil and the greyish look to the smear of oil (?) suggests it's material worn from the camshaft lobes and/or followers. Do these engines use an oil restriction/valve on the feed to the heads - these can be become blocked or stuck from fine debris and starve the head, but I think it's more than that with a fundamantal supply problem.

In short, looks like it has had an oil supply problem and a FULL strip down and careful inspection by an experienced builder will be in order to check just how bad the damage may be. At a minimum it's looking like full sets of main and big end bearings, maybe a pick-up and pump, and if you're really unlucky new camshafts.

Thanks again for your reply

I think your right with the oiling issue.

I have been all through the motor and haven’t found anything obvious.

everything was new when I re-assembled, ie new bearings , brand new kelford cams ,new cam cap bolts , total seal rings , nitto headgasket and the list goes on!

I stripped it bare and was cautious to clean everything carefully.

I used Penrite assembler lube and Penrite 30w run in oil.

checked oil pump, it appears to have billet gears and a crank collar also.

I primed oil pressure by vacuuming it through the turbo oil feed.

made 80-85 psi on first start.

it also has oil restrictors installed

I never built this motor originally but the previous owner looks to have addressed all the main RB issues.

Very often photos make bearings condition look much worse than their state. But if these pictures represent the real current state of bearings I would say there were lots of small debris in the oil. Not sure what caused it but definitely it needs to be traced and fixed... Scratches are way too deep for a fresh build.

Seems you did most things right, but maybe not so the builder..

Not sure what you meant by "vacuuming it through the turbo' oil feed"? If anything, I would expect it to pull oil out of all the other oil-ways - but if it's a commonly used AND EFFECTIVE, practice it's something to bear in mind. Did you mean pressure feeding it through the turbo' feed into the block, that would make sense?

For me, normal practice [might forget bit but basically] would be oil pump checked, cleaned and packed with oil soluble grease, so it has a strong vacuum right from the start to draw oil from the sump, all bearings lub'ed with anti-scuff paste/assembly paste and a few drops of oil, ditto with the camshaft(s) and other bearings, liberal amounts of anti-scuff or cam' lube. Engine filled with break in oil (if used), cranked (unless an external dry sump pump or pump driven by belt, where I would use a drill to turn the pump) with plugs out and any required electrics disconnected until oil pressure is shown and oil coming out of all follower oilways, turbo' feed if used, pushrods and rockers if used, etc. to make sure oil is getting all through the engine - there may be a fair bit of bubbling until that's bled out. Then jump the fuel pumps, if electric, until fuel is consistent from the return, or prime the carb(s) if used - this is to help starting with minimum of cranking. Then button up and connect everything and start the engine, keeping rpm up for splash lubrication of flat lifters if pushrod engine, while making initial check for leaks, funny noises, etc.

Then I'll drain that hot oil and refill with running in oil and a fresh filter - I'm very fussy about cleanliness* but they're cheap insurance for the fine dust, etc, that can find it's way inside, or the fine particles that are suspended in the oil during initial start up. Good time to check the filter for debris, too, in case something is showing up.

Then it's time to start driving it, or progressively loading it up on the dyno, to get the initial ring seal established, check for other issues like leaks, etc.

80PSI is about what I'd expect, but the guys familiar with the engine can better comment.

Hard to be sure, but it seems like the actual builder wasn't as careful as he/she should have been with cleanliness and assembly.

Following on from Shota's comment, I've had engines with bearings that were on their third (re-)build and still completely un-marked - basic engines and much lighter stresses, but still.