People with LS7 internals experience, need advice!
05-07-2015, 09:51 PM
#1
People with LS7 internals experience, need advice! Hi All,
I'm building an L92 4.00" stroker with LS7 Ti rods and custom Wiseco pistons. TSP is doing my block and supplying the crank and pistons. Since I'm doing the final assembly myself, they politely decline (due to liability issues) to give me advice on some rod related questions I have. It's a business decision, and I can understand their reasoning.
1) In another thread, Racer7088 (the very respectable Erik K) states the rod big-ends will need to be chamfered to clear an aftermarket crank's larger fillets. Is this something the "average" shop can do?
2) Do the factory rod bolts need replacing?
3) Do the rods orient the same on the crank pins based on the bearing tangs as other LS family rods?
Thanks!
I'm building an L92 4.00" stroker with LS7 Ti rods and custom Wiseco pistons. TSP is doing my block and supplying the crank and pistons. Since I'm doing the final assembly myself, they politely decline (due to liability issues) to give me advice on some rod related questions I have. It's a business decision, and I can understand their reasoning.
1) In another thread, Racer7088 (the very respectable Erik K) states the rod big-ends will need to be chamfered to clear an aftermarket crank's larger fillets. Is this something the "average" shop can do?
2) Do the factory rod bolts need replacing?
3) Do the rods orient the same on the crank pins based on the bearing tangs as other LS family rods?
Thanks!
05-09-2015, 01:36 AM
#4
The biggest issue we found is insufficient radial clearance in the piston boss's for the gudgeon pin, with some having as little .0005", this results in the rod being 'steered by the piston', which can and often will result in galling of the big ends thrust faces the second two rod's come into contact with each other.
The minimum clearance we work on is .0015" and the maximum is .0018" which should insure that the rod can align itself correctly.
Cheers,
Mark.
05-09-2015, 10:00 AM
#5
Whilst I can't comment on what may or may not be required to ensure the Titanium connecting rods, have a sufficient chamfer on the big end's to clear the radius on the crank pin, I do have a lot of experience with blue printing Titanium rods in our Ls7 engines.
The biggest issue we found is insufficient radial clearance in the piston boss's for the gudgeon pin, with some having as little .0005", this results in the rod being 'steered by the piston', which can and often will result in galling of the big ends thrust faces the second two rod's come into contact with each other.
The minimum clearance we work on is .0015" and the maximum is .0018" which should insure that the rod can align itself correctly.
Cheers,
Mark.
The biggest issue we found is insufficient radial clearance in the piston boss's for the gudgeon pin, with some having as little .0005", this results in the rod being 'steered by the piston', which can and often will result in galling of the big ends thrust faces the second two rod's come into contact with each other.
The minimum clearance we work on is .0015" and the maximum is .0018" which should insure that the rod can align itself correctly.
Cheers,
Mark.
As far as the LS7 rod, I haven't really used them on an aftermarket crank so I haven't really noticed this, but if it needs a chamfer any competent machinist shouldn't have any problem cutting it in a lathe. The orientation of the tangs isn't really that important; its where the chamfer is. I would ask the machinist to put the bearings in and cut the chamfer in the rod on the same side as the chamfer in the bearings.
05-09-2015, 05:59 PM
#6
Almost all GM engines are like this (except maybe the performance crate engines). I always see about .0006" tops on anything from a 5.3L to the LS7 so I usually bump the stock rods through the hone for about .001" clearance on a street engine.
As far as the LS7 rod, I haven't really used them on an aftermarket crank so I haven't really noticed this, but if it needs a chamfer any competent machinist shouldn't have any problem cutting it in a lathe. The orientation of the tangs isn't really that important; its where the chamfer is. I would ask the machinist to put the bearings in and cut the chamfer in the rod on the same side as the chamfer in the bearings.
As far as the LS7 rod, I haven't really used them on an aftermarket crank so I haven't really noticed this, but if it needs a chamfer any competent machinist shouldn't have any problem cutting it in a lathe. The orientation of the tangs isn't really that important; its where the chamfer is. I would ask the machinist to put the bearings in and cut the chamfer in the rod on the same side as the chamfer in the bearings.
With respect, its far less critical with steel rods if they touch, than it is with Titanium rod's, so you can afford to run .001" particularly with powdered metal connecting rod's because the machined surface has a lot more voids and asperities and thus a far greater ability to promote a hydrodynamic lubricating film, than forged steel billet rod's.
However, Titanium rods have zero ability to rub together even when they have been CrN coated, therefore the gudgeon pin need's at least .0015" clearance to be safe. Nascar typically run .0018" to .002" clearance on the wrist pin, and use very short pins [2"] and as small as .827" in diameter. Yes, I also know that all the Nascar wrist pins have DLH ceramic coatings, however, there are still lessons to be learnt in terms of gudgeon pin clearance that can be applied in critical application's, such as Titanium rods, at least in my opinion.
I would also urge caution when chamfering the Titanium big end, as the material itself is difficult to machine and you will also loose the CrN protective coating. Great care also needs to be taken when simply handling Titanium connecting rods because they are prone to notch failure if the surface is damaged.
Cheers,
Mark.
05-09-2015, 08:56 PM
#7
Appreciate all the new info to ponder over! According to my build sheet, TSP is supposed to "check" the parts for clearance, so hopefully the small end will fit inside the Wiseco's. My initial concern at the time (spec'ing the build) was - would the Wiseco piston on an LS7 rod clear the cheek on 4.00" crank? I hadn't even thought of some of the other things mentioned...
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05-10-2015, 12:42 AM
#8
Appreciate all the new info to ponder over! According to my build sheet, TSP is supposed to "check" the parts for clearance, so hopefully the small end will fit inside the Wiseco's. My initial concern at the time (spec'ing the build) was - would the Wiseco piston on an LS7 rod clear the cheek on 4.00" crank? I hadn't even thought of some of the other things mentioned...
Did you send one of your Titanium rod's to Wiseco piston's, or did you just assume they had the dimension's of a standard Ls7 rod?
05-10-2015, 07:52 PM
#9
Build sheet says "Custom Wiseco Pistons 4.07 bore, 4.00 stroke, 6.067 rod, -15cc dish, .9252 wrist pin, GFX rings". Wiseco builds pistons specifically for the LS7, so I'm sure they know of all the nuances. Hope it all comes out good, TSP was aware of the LS7 rods as I handed them over in person...
05-11-2015, 04:12 AM
#10
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Kcs got your comment backwards Kiwikid as he is talking about pin clerance but you are talking about small end with to piston pin boss clerance
That is called pin guided and used in circle track applications and then your rods b.e with is .840 instead of .940 wide for not binding it up on movement in endplay with crank thrust movement
With titanium you want more then .015 as they expand under heat more than steel
Any machine shop should be able to chamfer the rods on either the lathe or mill
Its allways a good idea to replace the rod bolts
That is called pin guided and used in circle track applications and then your rods b.e with is .840 instead of .940 wide for not binding it up on movement in endplay with crank thrust movement
With titanium you want more then .015 as they expand under heat more than steel
Any machine shop should be able to chamfer the rods on either the lathe or mill
Its allways a good idea to replace the rod bolts
05-13-2015, 02:31 AM
#11
Kcs got your comment backwards Kiwikid as he is talking about pin clerance but you are talking about small end with to piston pin boss clerance
That is called pin guided and used in circle track applications and then your rods b.e with is .840 instead of .940 wide for not binding it up on movement in endplay with crank thrust movement
With titanium you want more then .015 as they expand under heat more than steel
Any machine shop should be able to chamfer the rods on either the lathe or mill
Its allways a good idea to replace the rod bolts
That is called pin guided and used in circle track applications and then your rods b.e with is .840 instead of .940 wide for not binding it up on movement in endplay with crank thrust movement
With titanium you want more then .015 as they expand under heat more than steel
Any machine shop should be able to chamfer the rods on either the lathe or mill
Its allways a good idea to replace the rod bolts
Now you have me confused, I have only ever discussed the radial clearance in the rod's little end [small end] for the intended gudgeon pin [wrist-pin]
However we seem to agree on the need for at least .0015" over the diameter of the gudgeon pin, I like to see .0018" and would not be at all concerned with even .002"
Cheers,
Mark.
05-14-2015, 06:59 AM
#12
Hi KCS,
With respect, its far less critical with steel rods if they touch, than it is with Titanium rod's, so you can afford to run .001" particularly with powdered metal connecting rod's because the machined surface has a lot more voids and asperities and thus a far greater ability to promote a hydrodynamic lubricating film, than forged steel billet rod's.
However, Titanium rods have zero ability to rub together even when they have been CrN coated, therefore the gudgeon pin need's at least .0015" clearance to be safe. Nascar typically run .0018" to .002" clearance on the wrist pin, and use very short pins [2"] and as small as .827" in diameter. Yes, I also know that all the Nascar wrist pins have DLH ceramic coatings, however, there are still lessons to be learnt in terms of gudgeon pin clearance that can be applied in critical application's, such as Titanium rods, at least in my opinion.
With respect, its far less critical with steel rods if they touch, than it is with Titanium rod's, so you can afford to run .001" particularly with powdered metal connecting rod's because the machined surface has a lot more voids and asperities and thus a far greater ability to promote a hydrodynamic lubricating film, than forged steel billet rod's.
However, Titanium rods have zero ability to rub together even when they have been CrN coated, therefore the gudgeon pin need's at least .0015" clearance to be safe. Nascar typically run .0018" to .002" clearance on the wrist pin, and use very short pins [2"] and as small as .827" in diameter. Yes, I also know that all the Nascar wrist pins have DLH ceramic coatings, however, there are still lessons to be learnt in terms of gudgeon pin clearance that can be applied in critical application's, such as Titanium rods, at least in my opinion.
I'm confused as well now because the last set of titanium rods I had in my hands had bronze bushings in the small end so I'm not sure how surface to surface contact of titanium versus steel/PM is relevant with respect to the wristpin, as we Americans call it.
The chamfer shouldn't make contact with anything other than oil, hence the purpose of the chamfer.
05-14-2015, 09:31 AM
#13
Hi Kiwi,
I'm confused as well now because the last set of titanium rods I had in my hands had bronze bushings in the small end so I'm not sure how surface to surface contact of titanium versus steel/PM is relevant with respect to the wristpin, as we Americans call it.
The chamfer shouldn't make contact with anything other than oil, hence the purpose of the chamfer.
I'm confused as well now because the last set of titanium rods I had in my hands had bronze bushings in the small end so I'm not sure how surface to surface contact of titanium versus steel/PM is relevant with respect to the wristpin, as we Americans call it.
The chamfer shouldn't make contact with anything other than oil, hence the purpose of the chamfer.
My apologies, I just reread my own post and agree it is confusing, so lets try again.
With respect, its far less critical with steel rods if the cheeks of the big-ends touch, than it is with Titanium rod's, so you can afford to run .001" little-end clearance particularly with powdered metal connecting rod's because the big ends cheek's machined surface has a lot more voids and asperities and thus a far greater ability to promote a hydrodynamic lubricating film, than forged steel billet rod's, and thus keep the big-end cheeks from galling, should they touch each other
However, Titanium rods big-end cheeks have zero ability to rub together even when they have been CrN coated, therefore in order to allow the rod to align itself correctly [and not be steered by a tight gudgeon pin] the rods little end bushing need's at least .0015" clearance to be safe.
Comparatively large gudgeon pin clearance, in it self, is not a concern as Nascar typically run .0018" to .002" clearance on the wrist pin, and also use very short pins [2"] and as small as .827" in diameter. Yes, I also know that all the Nascar wrist pins have DLH ceramic coatings, however, there are still lessons to be learnt in terms of gudgeon pin clearance that can be applied in critical application's, such as Titanium rod alignment, for all the aforesaid reasons, at least in my opinion.
And I totally agree with your comment on the big-end chamfer, I hope my overly wordy explanation now makes sense.
Cheers,
Mark
Last edited by KiwiKid; 05-14-2015 at 09:39 AM.
05-14-2015, 08:34 PM
#14
Update: Got TSP to sub a GM LS7 crank for the Callies. I'll have to pay for another balance job ($230), but won't have to worry about trashing the rods. KCS mentioned going with a factory crank awhile back, but (since no reason was stated) I assumed it was more to do with the initial cost. I'm gonna get this done and do a write-up of what NOT to do...
On another note, vendor "A" tells me that the factory bolts need to be tossed for ARP's but all the literature I've seen says these rods cannot be resized. Vendor "B" says not to touch them, he's seen Ti rod failures, but never a rod bolt failure. Not sure about swapping rod bolts without a resize, anyone have experience with just a straight bolt swap? These freakin' bolts are $200 per set!
Note: Found an older (2008-ish) thread on another forum from vendor "A" stating the factory bolts are good for 3 re-torques before needing replacement. Found factory bolts for $7.44 per or $130 a set shipped...
On another note, vendor "A" tells me that the factory bolts need to be tossed for ARP's but all the literature I've seen says these rods cannot be resized. Vendor "B" says not to touch them, he's seen Ti rod failures, but never a rod bolt failure. Not sure about swapping rod bolts without a resize, anyone have experience with just a straight bolt swap? These freakin' bolts are $200 per set!
Note: Found an older (2008-ish) thread on another forum from vendor "A" stating the factory bolts are good for 3 re-torques before needing replacement. Found factory bolts for $7.44 per or $130 a set shipped...
Last edited by S10xGN; 05-17-2015 at 09:12 PM. Reason: rod bolt info/Q
05-16-2015, 06:22 AM
#15
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Hi Ari,
Now you have me confused, I have only ever discussed the radial clearance in the rod's little end [small end] for the intended gudgeon pin [wrist-pin]
However we seem to agree on the need for at least .0015" over the diameter of the gudgeon pin, I like to see .0018" and would not be at all concerned with even .002"
Cheers,
Mark.
Now you have me confused, I have only ever discussed the radial clearance in the rod's little end [small end] for the intended gudgeon pin [wrist-pin]
However we seem to agree on the need for at least .0015" over the diameter of the gudgeon pin, I like to see .0018" and would not be at all concerned with even .002"
Cheers,
Mark.
I took it as you where talking about side clerance on the rods to the piston as in pin guided
Those clerances are a bit excessive on a. 925/.927 pin as strength is in the larger diameter pin vs nascars .787 or even .708 diameter pins that need more room to flex and may have edm to keep oil there so its not something to directly translate over but would work
Last edited by Ari G; 05-16-2015 at 06:31 AM.
05-16-2015, 04:21 PM
#16
Hi Mark
I took it as you where talking about side clerance on the rods to the piston as in pin guided
Those clerances are a bit excessive on a. 925/.927 pin as strength is in the larger diameter pin vs nascars .787 or even .708 diameter pins that need more room to flex and may have edm to keep oil there so its not something to directly translate over but would work
I took it as you where talking about side clerance on the rods to the piston as in pin guided
Those clerances are a bit excessive on a. 925/.927 pin as strength is in the larger diameter pin vs nascars .787 or even .708 diameter pins that need more room to flex and may have edm to keep oil there so its not something to directly translate over but would work
Thanks for that. The reason we run such big clearances is to allow the rod to pivot very slightly in order to correctly align itself to the far greater width and diameter of the big end journal, as you will know a stock Ls7 Ti rod has a wedged small end, and by running .0015" the rod can self align more easily than it otherwise can if you run .0005".
Our road race engines are running at sustained comparatively high rev's, 6,800 rpm for long periods and we have never had a problem since we introduced the greater clearances.
Cheers,
Mark.
05-17-2015, 09:17 PM
#17
Added some edits in post #14 about the rod bolts.
Still haven't heard from TSP on whether the small end of these rods will actually "fit" up inside my custom Wiseco pistons. The pin bores were spec'ed to LS7 dims, just not sure because of the Ti rod small-ends being wedge-shaped...
Still haven't heard from TSP on whether the small end of these rods will actually "fit" up inside my custom Wiseco pistons. The pin bores were spec'ed to LS7 dims, just not sure because of the Ti rod small-ends being wedge-shaped...
05-19-2015, 04:46 AM
#18
Added some edits in post #14 about the rod bolts.
Still haven't heard from TSP on whether the small end of these rods will actually "fit" up inside my custom Wiseco pistons. The pin bores were spec'ed to LS7 dims, just not sure because of the Ti rod small-ends being wedge-shaped...
Still haven't heard from TSP on whether the small end of these rods will actually "fit" up inside my custom Wiseco pistons. The pin bores were spec'ed to LS7 dims, just not sure because of the Ti rod small-ends being wedge-shaped...
The LS7 rods are fairly crappy though so I don't like using them in general anyway. They always have metal transfer between the upper rod bearing at 10 and 2 o clock in the upper rod housing bore so I assume they flex a lot but anyway it's not really a good deal but I've done many of them for people and they seem to stay together.
05-19-2015, 06:48 AM
#19
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Can ARP rod bolts be swapped in without a re-size? Are the stock rod bolts safe to be reused as long as it's the first time the Ti rods are out of the motor? I'm finding some conflicting info out there.
05-19-2015, 07:40 PM
#20
I've done tons of pistons with LS7 rods and just did two more last month so as long as Wiseco knew your LS7 rod dimensions fitment should be easy. It's just a rod. The main problem is with the super thick top of the small end. I just get them at .927 and hone the LS7 rod small ends out a lil so if you have any issues later or freshen it you can do that as well. There's not too many .9252 pin choices!
The LS7 rods are fairly crappy though so I don't like using them in general anyway. They always have metal transfer between the upper rod bearing at 10 and 2 o clock in the upper rod housing bore so I assume they flex a lot but anyway it's not really a good deal but I've done many of them for people and they seem to stay together.
The LS7 rods are fairly crappy though so I don't like using them in general anyway. They always have metal transfer between the upper rod bearing at 10 and 2 o clock in the upper rod housing bore so I assume they flex a lot but anyway it's not really a good deal but I've done many of them for people and they seem to stay together.
I too, would love a definitive answer! There's been all kinds of things said over the years from top-notch vendors, so I'm ASSuming some things have changed through time. For now (unless I get a better answer), I'll be using a new set of stock bolts. Would love to use the ARP's, but not w/o knowing about the potential out-of-round issues...