rb25det camshaft drama!

I have spent the last few weeks giving my rb25det a freshen up.

After diagnosing a damaged journal bearing i have replaced both main & rod bearings along with some new rings . This motor has Ross racing pistons , RB26 rods and a full catalogue of ARP stud & bolts.

I have followed the fundamentals of this rebuild to the letter and have studied this course as this is my first rebuild.

Felt as though i was almost done with this until i have hit a very strange hurdle!

Fitted a new Nitto 1.2mm head gasket and then installed the head, and exhaust cam with no problem...

Then i installed the intake cam and torqued to spec only to find the cam is locked solid?

I have repeated the install process about a dozen times now and no matter what i do it remains locked...

So far i can eliminate timing direction, valve to piston clearance, torque specs, valve movement and have installed cam with head both on and off block.

Next stage i guess is remove the head again and strip the head down to try find some reasons

Can anybody shed any light on this or is there something i am missing??

7 days and counting before a upcoming drift event...!>

Did you put the cam caps in the right order you took it out?

yes is have, i have triple checked everything and also compared placement to another rb25 i have here.

Hmmm, about the only other things that come immediately to mind is if the camshaft is bent slightly (this can even happen during removal/installation from spring forces) or, if you're using ARP studs the greater tensile loading is distorting the head and/or cap slightly and it's closed up on the camshaft journal(s)?

It's more messing around, but perhaps if you fitted the camshaft on the bare head (so there's not lobe contact to followers/valves) and checked how it turned when lightly oiled, or maybe with some engineer's blue instead, to see where some 'blue is rubbed of more than others? Then fitted the caps one by one to see if there is a tight spot, or cap?

Thanks for your input Gord ,

this is something that I have been thinking about is the head studs.

As they are torqued to 80 lbf.ft they are definitely tight!

first thing il do today is prove that cam is straight and go from there.

I have read a few articles on the correct bolting sequence for install and removing and this is definitely some grey areas around that so the chance it has been damaged is getting higher.

will report back shortly.

thanks again for reply’s.

I was thinking of the camshaft cap studs/bolts, rather than the head bolts/studs.

If used, they are normally a relatively coarse thread where they screw into the head, like OEM, but use a finer thread for the nut and because of the shallower thread angle a greater tensile - clamping - force can be applied, and this can cause the alloy to distort slightly. Same problem which can occur with crankshaft main bearing caps/girdles with aftermarket studs.

With many DOHC engines, the camshafts are made with the same journal sizes and positions - if you can swap them over, it may help identify if it's a camshaft or a head issue? From what you say, looking more like a camshaft issue - if you don't have a couple of "V" blocks and a good DTI, your engine machinist should have them, to check the cam' for run-out.

Ok so bad news but at least iv found the issue.

bent cams!

badly too , 2+ mm

So that has answered that question, now my next question is how??

what did I do wrong to cause soo much damage?

It happens when you have stiff valve springs and remove camshaft caps in wrong sequence... Sometimes it can even cause camshafts to break apart in two pieces...

Your not wrong! I’m pretty confident I have balls up the removal sequence.

definitely have a new respect for how precious these can be.

That sucks, and not in a good way!

Unless you've knocked them over, or dropped them - unlikely as you'd've mentioned it - it may have been due, as mentioned above, to incorrectly removing or fitting the camshaft(s). There are ways of removing, and refitting, that minimise the stress on the shafts, but a bit difficult to go into here (if you want my thoughts, though, ask) - might be something in the manual?

Most people don't realise the caps are restraining the camshaft against the force of the valve springs and simply remove the caps from one end to the other. The problem is if the end that was started at had the lobes at the fully open position, or close to it, there may be several hundred pounds/kilograms of force bending the shaft by the time the last caps were removed - same thing applies when refitting it/them. I think that's what happened here.

"In theory", they can be straightened by a skilled mechanic/engineer with a hammer and soft drift - DO NOT USE A PRESS! - same as a crankshaft, but getting it right is darned difficult, and it's easy to break them.

Thanks again for your input Gord

valuable lessons learnt here!

you are right in saying I got the sequence wrong, I learnt this shortly after this all started realising i used the install sequence as a removal sequence.

anyway moving forward from here I will take this opportunity to upgrade the cams anyway and definitely treat these with more respect!

I do appreciate all your input as this is a steep learning curve for me but still enjoying the process.