ZRP Forged Conrods
Discussion
Interesting observation. I am working on an MGB engine with big end failure with cheap rods, we will be using Robson rods in the rebuild. The big end of the rod evidenced blackened areas in at least four places on each rod showing it wasn't round in use, probably the reason for the failure. Not one of my builds as I do not feel right using the cheap rods. They don't even look the same quality as the likes of Saenz, Robson/Farndon, Carillo, Arrow etc. I haven't seen anyone pick out the cheap rods when you say to folk which would you use and let them compare. We had a set of rods sent by a customer that we refused to use. Even the little end bush was too small for the gudgeon pin to go through!
People will continue to buy them as they convince themselves with the price and on the net they do look similar to the higher price rods.
Peter
People will continue to buy them as they convince themselves with the price and on the net they do look similar to the higher price rods.
Peter
PeterBurgess said:
Interesting observation. I am working on an MGB engine with big end failure with cheap rods, we will be using Robson rods in the rebuild. The big end of the rod evidenced blackened areas in at least four places on each rod showing it wasn't round in use, probably the reason for the failure. Not one of my builds as I do not feel right using the cheap rods. They don't even look the same quality as the likes of Saenz, Robson/Farndon, Carillo, Arrow etc. I haven't seen anyone pick out the cheap rods when you say to folk which would you use and let them compare. We had a set of rods sent by a customer that we refused to use. Even the little end bush was too small for the gudgeon pin to go through!
People will continue to buy them as they convince themselves with the price and on the net they do look similar to the higher price rods.
Peter
Whose rods were they and do you have any pictures?People will continue to buy them as they convince themselves with the price and on the net they do look similar to the higher price rods.
Peter
I don't know the make as I didn't build the engine originally, the owner told me they were 'cheap' rods to save money, the varying thickness of the beam looks like the cheap rods many folk are tending to use, I have not seen this variation in quality rods. I am not at work at the moment but will take some pics and big end measurements when I am back to work. I will take some side by side pics of the Robson rods we drew up and had made for comparison purposes.
Peter
Peter
Interesting to hear.
Am going to take time to have these rods properly inspected to see if there is any difference in each rod, confirm they're straight etc before (assuming all is well) using them. As mentioned earlier, the supplier also actually use these rods in their VAG engine builds and haven't experienced any failures due to quality control.
Are there any specific measurements & checks you can suggest?
Am going to take time to have these rods properly inspected to see if there is any difference in each rod, confirm they're straight etc before (assuming all is well) using them. As mentioned earlier, the supplier also actually use these rods in their VAG engine builds and haven't experienced any failures due to quality control.
Are there any specific measurements & checks you can suggest?
I reckon do what James says above, check the rods for roundness with a bore gauge, crack the nuts/bolts off then re stretch them (to the prescribed amount by the rod supplier)and check them for roundness again. If all is well there should be no measurable ovality as the rods are new and unused (hammered).
To measure the stretch we bought one of these from Demon Tweeks ........http://www.demon-tweeks.co.uk/motorsport/hand-tools/arp-rod-bolt-stretch-gauge it is a pleasure to use.
Peter
To measure the stretch we bought one of these from Demon Tweeks ........http://www.demon-tweeks.co.uk/motorsport/hand-tools/arp-rod-bolt-stretch-gauge it is a pleasure to use.
Peter
Mignon said:
Would anyone like to post a comprehensive list of the recommended prep operations and checks to do on a new set of conrods?
Realistically most buying cheap rods wouldnt have the gear to do most anyway.At a minimum I guess it should be straightness, weight...end-end weights and torque em up and measure the big holes in the middle to ensure round and correct dimensions. Something plastigauge will never do
I agree with the above points mentioned.
Out of round with bolts torqued up using correct lube, diameter also.
Always torque up bolts 5 times to bed them when final fitting.
Weight. I found this important and very easy as a set of dealer scales are cheap as chips on Ebay. I did have PEC send me a set with one rogue rod once which weighed a lot more than the others so was glad I checked.
As they are likely to be pretty good then you won't need to do an end over end balance, but if you did (say they were Robsons) then that's a whole different story....
I very much doubt you'll find a new rod having any twist or bend as it's pretty difficult to machine something that way, but checking is piss easy: Put one rod flat against the other, but end for end different (small against big) and see if they rock or sit flat against each other.
Lenght? Well again, vanishingly unlikely they'll be out, but I can't think of many ways to check accurately or easily. Sliding verniers will be 'something like' in the right hands, and other type of measuring device for that will be pretty much out of range for most. Checking deck height when assembled would be useful.
And a visual check of course, machining marks, sharp bits, damage.
As I mentioned earlier any non destructive strength testing is going to be difficult to do....
Oh and never buy unbranded rods, asking for trouble that is.
I did some investigation into how one of the openly Chinese vendors was managing to sell a decent rod for so little money as I was suspicious. It turned out to be not only lack of mark up, but moreover the way they were er, getting them into the country and distributing them without attracting any 'additional charges'.
Out of round with bolts torqued up using correct lube, diameter also.
Always torque up bolts 5 times to bed them when final fitting.
Weight. I found this important and very easy as a set of dealer scales are cheap as chips on Ebay. I did have PEC send me a set with one rogue rod once which weighed a lot more than the others so was glad I checked.
As they are likely to be pretty good then you won't need to do an end over end balance, but if you did (say they were Robsons) then that's a whole different story....
I very much doubt you'll find a new rod having any twist or bend as it's pretty difficult to machine something that way, but checking is piss easy: Put one rod flat against the other, but end for end different (small against big) and see if they rock or sit flat against each other.
Lenght? Well again, vanishingly unlikely they'll be out, but I can't think of many ways to check accurately or easily. Sliding verniers will be 'something like' in the right hands, and other type of measuring device for that will be pretty much out of range for most. Checking deck height when assembled would be useful.
And a visual check of course, machining marks, sharp bits, damage.
As I mentioned earlier any non destructive strength testing is going to be difficult to do....
Oh and never buy unbranded rods, asking for trouble that is.
I did some investigation into how one of the openly Chinese vendors was managing to sell a decent rod for so little money as I was suspicious. It turned out to be not only lack of mark up, but moreover the way they were er, getting them into the country and distributing them without attracting any 'additional charges'.
One key thing with budget rods is they save money on any kind of marking or identification. Getting a cap on the wrong way or on the wrong rod is a sure way to destroy an engine. Saying that I did see an Aston engine poorly built with Arrow rods that had a cap and rod mismatch and it had survived! Says something about accuracy.
So before you get a socket or spanner near the bolts, mark the rods either side of the split line in some way, marker pen if your careful, etching pencil Maplins were doing a cheap battery one, marking fluid and a scriber works and makes an easy check before you bang the sump on. Stamping isn't great practice.
So before you get a socket or spanner near the bolts, mark the rods either side of the split line in some way, marker pen if your careful, etching pencil Maplins were doing a cheap battery one, marking fluid and a scriber works and makes an easy check before you bang the sump on. Stamping isn't great practice.
It seems I'll have to do it myself. Here is a list of the basic checks and prep operations that should be done on new rods.
1. Remove the bolts and make a visual check that the bolt holes are central within the width of the rod material. With vernier calipers measure the wall thickness of the material either side of each hole. Imagine an 8mm hole in a 14mm wide rod. There should be exactly 3mm of metal on either side of the hole. If the hole is 0.1mm off centre then the wall thickness will be 3.1mm one side and 2.9mm the other i.e. the difference is twice the offset. Ideally the bolt should be central within 0.2mm giving a difference of less than 0.4mm. I rejected a set of cheap rods a friend had bought some time ago when one bolt was so far off centre it had only 1mm material on one side and 4mm or so on the other.
Make sure the eccentricity, if present, is the same at both the bottom and top of the cap and where the hole exits the rod. Any change in the offset means the bolt hole is not perpendicular to the rod axis.
2. Holding each bolt with just your fingers wind it right up and down the thread in the rod. If there is any tightness try with another bolt to check whether the problem is with the bolt or the thread. All threads should be smooth and friction free.
3. One of the most important areas is where the bolt head sits on the cap. Each hole in the caps should be chamfered to clear the fillet radius between the shank of the bolt and its head. Check that the chamfers are sufficient and the same on each cap. The surface where the bolt head sits should be flat and smooth with no chatter marks or burrs. Place a bolt in each hole in the loose caps and with fingertip pressure on the top of the bolt make sure it sits flat and doesn't rock. If you have engineer's blue you can check the seating.
4. With a small engineer's oilstone (1/2" x 1/2" x 4") lightly chamfer all along the split lines between rod and cap to remove any burrs.
5. With a larger oilstone or chisel sharpening stone give each cap and rod a few light strokes along the split line. Place each cap back on its rod without bolts and holding the two together by hand hold the split line up to a bright light and make sure no gaps are visible.
6. Deburr the sides of each big end hole if any marks are visible.
7. Do the same for each little end bush.
8. Insert each pin in its bush. Check that the pin rock is barely detectable and the same on each rod. If you have a dial gauge then put each rod flat on a metal surface, insert the pin so it's flush with the table and mount a dial gauge at the top of the pin. Measure the total pin rock. Using the pin rock equation here..
http://www.pistonheads.com/gassing/topic.asp?t=749...
Calculate the pin to bush clearance. It should be less than 0.5 thou.
9. Fully floating pin rods should have an oil hole in the top of the rod through to the bush and this should be well chamfered.
10. With fully floating rods the length, straightness and twist can be checked very easily without special tools. Connect two rods together using a gudgeon pin through both little end bushes. Make sure the big ends can be aligned to sit flat against each other in both planes. With a straight edge through the big end bores make sure both rods are the same length. If there is a gap between the straight edge and one rod measure it with feeler gauges. Picking one rod as a datum and checking the rest against it all should be within 2 thou of each other in length.
This check is facilitated if you mount a long bolt or metal bar horizontal in a vice so you can hang the rods on it through the hole in the gudgeon pin.
11. Special jigs are needed to check the balance of big and little end mass end over end but total weight can be checked easily with cheap digital scales. 1 gram is adequate. Measure each cap separately. Any greater difference here might indicate that either the rod centre to centre lengths are not the same or there is an error in weight balance end over end.
12. Measure the widths of each big end and verify against a stock rod or specifications. Side to side play in the crank should also be checked at the build stage.
13. If you have bore gauges then check each big end for size and ovality.
14. Seat an old big end shell in each rod to verify it sits central i.e the shell tab locators are in the correct place.
1. Remove the bolts and make a visual check that the bolt holes are central within the width of the rod material. With vernier calipers measure the wall thickness of the material either side of each hole. Imagine an 8mm hole in a 14mm wide rod. There should be exactly 3mm of metal on either side of the hole. If the hole is 0.1mm off centre then the wall thickness will be 3.1mm one side and 2.9mm the other i.e. the difference is twice the offset. Ideally the bolt should be central within 0.2mm giving a difference of less than 0.4mm. I rejected a set of cheap rods a friend had bought some time ago when one bolt was so far off centre it had only 1mm material on one side and 4mm or so on the other.
Make sure the eccentricity, if present, is the same at both the bottom and top of the cap and where the hole exits the rod. Any change in the offset means the bolt hole is not perpendicular to the rod axis.
2. Holding each bolt with just your fingers wind it right up and down the thread in the rod. If there is any tightness try with another bolt to check whether the problem is with the bolt or the thread. All threads should be smooth and friction free.
3. One of the most important areas is where the bolt head sits on the cap. Each hole in the caps should be chamfered to clear the fillet radius between the shank of the bolt and its head. Check that the chamfers are sufficient and the same on each cap. The surface where the bolt head sits should be flat and smooth with no chatter marks or burrs. Place a bolt in each hole in the loose caps and with fingertip pressure on the top of the bolt make sure it sits flat and doesn't rock. If you have engineer's blue you can check the seating.
4. With a small engineer's oilstone (1/2" x 1/2" x 4") lightly chamfer all along the split lines between rod and cap to remove any burrs.
5. With a larger oilstone or chisel sharpening stone give each cap and rod a few light strokes along the split line. Place each cap back on its rod without bolts and holding the two together by hand hold the split line up to a bright light and make sure no gaps are visible.
6. Deburr the sides of each big end hole if any marks are visible.
7. Do the same for each little end bush.
8. Insert each pin in its bush. Check that the pin rock is barely detectable and the same on each rod. If you have a dial gauge then put each rod flat on a metal surface, insert the pin so it's flush with the table and mount a dial gauge at the top of the pin. Measure the total pin rock. Using the pin rock equation here..
http://www.pistonheads.com/gassing/topic.asp?t=749...
Calculate the pin to bush clearance. It should be less than 0.5 thou.
9. Fully floating pin rods should have an oil hole in the top of the rod through to the bush and this should be well chamfered.
10. With fully floating rods the length, straightness and twist can be checked very easily without special tools. Connect two rods together using a gudgeon pin through both little end bushes. Make sure the big ends can be aligned to sit flat against each other in both planes. With a straight edge through the big end bores make sure both rods are the same length. If there is a gap between the straight edge and one rod measure it with feeler gauges. Picking one rod as a datum and checking the rest against it all should be within 2 thou of each other in length.
This check is facilitated if you mount a long bolt or metal bar horizontal in a vice so you can hang the rods on it through the hole in the gudgeon pin.
11. Special jigs are needed to check the balance of big and little end mass end over end but total weight can be checked easily with cheap digital scales. 1 gram is adequate. Measure each cap separately. Any greater difference here might indicate that either the rod centre to centre lengths are not the same or there is an error in weight balance end over end.
12. Measure the widths of each big end and verify against a stock rod or specifications. Side to side play in the crank should also be checked at the build stage.
13. If you have bore gauges then check each big end for size and ovality.
14. Seat an old big end shell in each rod to verify it sits central i.e the shell tab locators are in the correct place.
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