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Fabricating Engine/gearbox Mounts For Rb25 Conversion... Positioning And Angles (Inc. Sexy Rb25Det Neo Pics! ;-) )


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#1 Dan260Z

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Posted 31 March 2016 - 07:40 AM

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So finally, almost 6 years into the worlds slowest zed build, I have the RB sitting in the bay of my '74 2+2!
 
Not a fan of the conversion kits I've seen that use round poly bushes (eg. CX racing)... would like more damping than that, hence I'd like to use the original R34 RB25DET mounts (or something OEM) combined with a custom bracket.  Same with the gearbox (R33 turbo 5-speed).
 
I'm handy with metalwork so the actual fabrication isn't a problem.  But I'm stuck with getting the motor and gearbox sitting in the right position and on the right angle (relative to the diff, an R200 longnose).  Currently the motor is just sitting on a strip of timber on the crossmember (temporary hack job rear bowl sump fitted while I mod the RB one to clear the crossmember), while the rear of the gearbox sits on blocks. Plan was to jimmy, shim and nudge the whole shooting match up down, left right, etc until it was in the right spot, take measurements, and fabricate the mounts to keep it in that position.
 
I've done a little reading on how to get the angles right (eg. http://www.rustynuts...m/driveline.htm) but I'm curious to see how others here have done it, specifically with an S30.  
 
Things I'd love to find out if you've done an RB conversion:
- How high above the crossmember is the bottom of your block at each side?
- How high does the rear of the gearbox sit relative to the top of the tunnel?
- Is your shifter sitting in the middle off the opening in the left-right axis? (which places it offset towards the drivers side, since the opening isn't centered, nor is the diff, they're both more towards the drivers side, making me think the crankshaft has to be too?)
- Any other measurements that might help?  Eg. from the side of the block to the chassis rail?  
 
Realise I'm asking a lot - but if anyone's willing to spend some time with a tape measure, I'll do a write up with mount drawings, etc, and make a donation to the site (actually I'll prob do that anyway since it's been a while since I have ;-) )
 
Any other info appreciated also - eg. problems you had down the line due to misalignment, experience with existing kits, etc, etc.
 
Cheers!!! :)
 

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#2 260DET

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Posted 31 March 2016 - 08:55 AM

There probably have been misalignment problems but I'd guess that most swaps have been successfully done by merely centralising the engine/gearbox plan wise and then getting the back of the gearbox to point at the diff and that's it. But I am not familiar with the RB25 swap which could be done by replicating the L engines crankshaft line if you want to replicate the factory alignment. Of course there are ways to check tailshaft angles if you want to do it by the book.

 

It will be interesting to see if you get a response with measurements, happy to be shown wrong but I'm betting no one has them :)


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#3 Dan260Z

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Posted 31 March 2016 - 11:17 AM

I suspect you'll be proven right, but I'm hoping otherwise :)

 

Even if someone with an RB's zed could quickly chuck a tape measure across a few spots so I could get a vauge idea of where the engine sits, where the crankshaft centre is relative to the frame rails, etc it'd be super helpful.

 

And personal experiences will help, eg if someone says "I used the "blah brand" mounts and my tailshaft UJ's are still fine after 50,000kms" or "I just slapped the motor in however it fit and everything's fine".

 

Unfortunately I sold my L26 ages ago and didn't take any measurements before removing it.



#4 andyk_79

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Posted 04 April 2016 - 06:23 PM

I suspect somewhere on hybridz the answer lies. A lot more modded discussion there. This thread is a good starting point:
http://forums.hybrid...re-ya-go/page-3

#5 PeterAllen

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Posted 04 April 2016 - 07:08 PM

As someone who has been down the tortuous hybrid build path I strongly recommend you buy as much off-the-shelf stuff as you can. It's not so much the fabrication of item but the problems with interconnectedness associated with other items, e.g. exhaust pipes and engine mounts.

 

Just a suggestion, but have you considered making your own bushes, with a lower Shore hardness, to fit the off-the-shelf mounts?



#6 nizm0zed

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Posted 04 April 2016 - 07:24 PM

Im fairly certain I mentioned what combo of engine mounts I used in my conversion in my build thread (Somewhere in the last few pages) but from memory its the stock RB25 engine mount brackets onto R31? rubber mounts fitted to the stock crossmember.
The sump is obviously custom but everything clears nicely.
I have thermo fans fitted so I cant comment on the OEM RB viscous fan, but I have a feeling it may just squeeze in.
The gearbox mount was 100% scratch built by me and I was able to use my stock 260z manual tailshaft, the spline and length was perfect.
I used the non turbo RB25 box though, its slimmer. I know the turbo box needs mods to the trans tunnel, it doesnt clear past the crossmember mounts on the body.



#7 Dan260Z

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Posted 13 April 2016 - 12:31 PM

Cheers guys, very helpful so far.

 

From memory that hybrid z build page didn't answer my qns but I'll take another look and see what else is on the site that might help.

 

Good idea re. the custom urethane for the mounts - will certainly consider it.  I'm just not convinced which, if any, of the off-the-shelf mount manufacturers have considered stuff like proper tailshaft alignment.  Anyone can sell something that'll work for a while... who knows if a rarely-driven project car chewed out the tailshaft UJ's 25,000kms down the road... or had a slight mystery vibration due to mismatched front and rear UJ angles. Plus there's lots of reports of the CRS stuff sitting the engine too high and forward, the CX racing stuff has little rubber between the centre and the edges so is likely to cause the car to vibrate, etc, etc.

 

Will check out your build page, cheers for that, had no idea that a combo of stock parts would line up.  I do have an RB25 turbo box, but I've already cut the original gearbox mounting ears off the tunnel back when the car was on the rotisserie.

 

Anyone know if nat0_240_chevZ is still making mounts and sumps?  PM'd him a while ago but no reply.  Even just to pick his brain would be great.

 

Meanwhile, here's my progress so far, with the custom sump mods.

 

 

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#8 PeterAllen

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Posted 13 April 2016 - 02:33 PM

This will probably just confuse your decision-making even further but I'll post it anyway.

 

The John's Cars Inc (JCI) mounts from Texas are the most popular LS1 engine swap. They actually sit the engine 25mm offset to our driver's side. JCI has never offered an explanation why this is so. Some have speculated it is to offset the weight of the driver in a LHD car and others suggest it simply allowed for the best fit overall.

 

By coincidence when I installed the Holden LSD diff the input shaft is 20mm offset to our driver's side which creates an almost perfect sideways alignment with the LS1 gearbox output. I made the gearbox and diff mounts angled on the vertical plane to further ensure alignment. As a result I used Jurid couplings (rubber coupling) from the VZ SS Ute donor car on both ends of the tailshaft.

 

Prior to going down this path I discussed this concept with a genuine drivetrain guru (Ford research engineer) and he stated the Jurid couplings were good if the compound angle of the tailshaft didn't exceed 4 degrees, i.e. offset on the 'x' axis and the 'y' axis combined didn't exceed 4 degrees.

 

So, if you are struggling to get enough angle on the unis to avoid brindling you might want to consider actually straightening out the alignment and fitting Jurid couplings. Arr... the joys of hybrid builds!

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Edited by PeterAllen, 13 April 2016 - 02:35 PM.


#9 Dan260Z

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Posted 04 May 2016 - 10:36 PM

Thanks Peter, and sorry for this slow reply - zed work sessions have been few and far between this year with family life taking up a lot of time.

 

Interesting that they offset it 25mm... since last night I got out the tape measure and measured the diff pinion offset relative to the body (measured off the the points where the doglegs are spot welded to the other layers in that area) and it came up as roughly 25mm offset towards the drivers side (68mm from the passenger side, 63 from the drivers).  From that I'm assuming the crank has to be 25mm towards the drivers side too (and in turn, I assume that why the RB and presumably (?) the L series is on an angle leaning towards the passenger side... perhaps to centre up the weight while allowing the crank to be offset?

Of course I don't know yet if the RB gearbox (RB25DET R33 gearbox) has an offset output shaft already... only just thought I should check that before I go about offsetting the crank.... hmmmm.

 

While I was at I got out the digital angle gauge I finally received from DX and measured the diff nose angle relative to the flat section under the rear suspension crossmember (the bracket that clamps the front bushes to the chassis).  Came up almost exactly 4 degrees, nose up.  I do have an RT style diff mount, but it's not making contact when static, so only the stock mustache bar and lower nose mount should be in play (ie. that should be the stock angle).

 

Enging/gearbox "looks about right" when it's close to 4 deg too... so I assume if I design the mounts to angle it at 4 deg (gearbox down), the tailshaft angles will match at each end and cancel out oscillations in angular velocity (well... I assume thats the aim anyway... more research to be done there!)

 

Getting the RB tilted over properly should be easy... there's flats on the timing cover that are supposedly supposed to be level when the motor is tilted... sticking the angle gauge on those (Set to measure relative to the radiator support) should help me get the motor tilt right.

 

Love the idea of the jurid couplings... though straightening out the diff might be tricky without a bit of fab work... dunno how I could drop the nose without ditching the stock lower mount or raising the back by modifying the mustache bar?

And the motor might be tricky too... only so much I can lower the front before the sump (rear bowl) hits the crossmember, and the gearbox starts to hit the upper areas on the tunnel well before I get it to 0 degrees.

 

Any further thoughts welcome though!  


Edited by Dan260Z, 04 May 2016 - 10:39 PM.


#10 nat0_240_chevZ

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Posted 05 May 2016 - 10:58 PM

G'day Dan.
Yep still alive.... Same dramas, demanding family commitments.
I have documented quite alot and on CAD too, especially the build of my mounts.
The l-series, Rb and most inline 6's I've come across are leant over. Bar a few, ie ford and Toyota.
The correct amount of 'lean' I found on the Rb, as I was able to demonstrate with one of my r34's sitting next to my zed at the time, with the front stripped off it, took heaps of pics too.
Is the inlet cam, dead above the crank centre line. And as such the engine cover was dead level in the bay.
The lean you note, Still, believe it or not, puts the CoG almost bang on in the centre of the engine bay for the eng / gbox assy. Thus neutralising any perceived weight bias laterally.
From memory the front nose of the crank was in fact off centre, with the l-series and with the Rb I kept the much the same.

When making my mounts, I have a few variations, which were acquired along the way, 1st successful placement is the 'stock' pos'n, from there I had 2 or 3 variations suitable depending on owner preference, but also gbox and engine position requirements as well as tailshaft length.
Opt.1 = stock tailshaft, with an rb30/20 71C gbox.
Opt. 2 = stock tailshaft length although modified output yolk with rb25 box (the big one) I used r34 gtt everything for this fit in early 71 tunnel, so ears not a problem, but still very tight, and needs a remote speedo sender.
Opt. 3 = shorter, modded tailshaft. With Rb20/30 box, but 20mm lower engine height nominally but 50mm more rearward of eng/gbox assy, for even lower CoG and more neutral front rear weight bias.
I could dig out my CAD drgs and clarify edit what I have written above, ie the lean direction I could be back to front from memory... Lol
As for diff angle, I still have one shell on a chassis jig I made with the car clocked in based on the FSM chassis diagram, Datums.'C' and jig holes under the car at 100mm square pitches,
I found the natural offset of the crank & gbox gave plenty of Mis- alignment, but the gbox output was pointing almost directly at the input on the diff (give or take 2-3mm) And 2.8deg (from memory again) due to this.

I'll dig something out and post a pdf from the cad data, or a pic of it.
Nat0

#11 nat0_240_chevZ

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Posted 05 May 2016 - 11:04 PM

Oh and remember, the Rb is almost the same engine as the l-series.
Just think, the bore spacings are the same as are the head bolts centres.
The Rb is the evolution of the L.
No doubt about it.
Much the same as the z18det on the l20b, as their heads are interchangeable.
Nat0

#12 Dan260Z

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Posted 05 June 2016 - 08:40 PM

Cheers mate really appreciate all that info... and sorry its taken me yet another month to get back in here! Think I've spent about 10hrs on the car during that whole month :(

Cool re. The lean, seems easy enough to get right. Been using a digital angle gauge with a relative function to get it level with the radiator support.

I've got an R33 gts-t gearbox so that decision is made. Haven't thought much about the tailshaft yet, just focusing on getting it all lined up and mounted first. I've certainly seen what you mean by the speedo sender fouling though!

The snag Ive hit today when attempting again to get it all sitting right, was when I tried matching the engine/gearbox left/right offset with that of the diff input shaft. I found the diff to be about 25mm offset towards the drivers side. But if I move the crank and gearbox outout shaft over that far(with the engine tilted correctly), the gearbox hits the tunnel (speed sender removed) and the engine looks too close to the steering shaft. Amd the bellhousing hits the fuel lines. See attached pics. Any ideas on this? I noticed the shifter cutout in the tunnel is only offset 10mm despite the diff input being 25mm over... perhaps the crank should only be offset by 10mm?

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Edited by Dan260Z, 05 June 2016 - 08:49 PM.


#13 Dan260Z

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Posted 05 June 2016 - 08:43 PM

Oh forgot to mention if you have any info/CAD etc you be willing to send me I'd be ridiculously appreciative! Be happy to pay for the info... beer, money, site donation, etc.

Even just knowing what the crank offset is between the frame rails when a factory L series is fitted would be awesome if you or anyone else have a few mins and a tape measure!

Edited by Dan260Z, 05 June 2016 - 08:45 PM.


#14 nat0_240_chevZ

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Posted 08 June 2016 - 09:46 PM

It is offset to one side, but as the engine is on a lean, the COG(centre of gravity) is pretty much central between the 2 rails, although the crank
The nose of the crank from memory is about 15mm- to one side. Check my engine mount thread/topic, got a fair bit of Info in that.
I'll be digging into an old backup as I lost a CAD dedicated HDD, last month. The backup should have it but.
The crank points towards the tails shaft pinion, from one side of the car to the other, about 2.5 degrees roughly. Again all from memory. There are some good pics of the Z on google images showing a partially see through car from the top, and you get an awesome perspective of the drive line alignment from above.
I'll do so. E digging and see what I find.
In the meantime, look for my engine mount thread, as I'm only surfing via my phone e of late and struggle to multitask on phone browser.
Nat0


Edited by nat0_240_chevZ, 09 June 2016 - 11:55 PM.


#15 Dionysus

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Posted 09 June 2016 - 10:34 AM

Just reading through, how did you go with the box? Rb25 boxes are quite large but at the same time much stronger that other RB units.

 






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