Post #34
It's a long time since I used JEs, it's been CP/Omega only and Carrillo/Robson rods as WP says for the last 4 years or so. Before anyone asks, I don't sell my specials, I'm not into selling parts, they are only for my builds. I have looked at working out some middle of the road designs for a friend of mine to sell through his business, because it frustrates me not being able to offer people a solution.
The issues with the design and manufacturing quality of Wossner/PEC pistons and rods, may not always be obvious and there are alot of engines using them, that haven't flagged the risk yet. It's a long time since I've seen an XU piston from them, but I recall the intruders and pockets needed to be machined to give safe clearance. The TU ones will rub the intruder and valves quite easily unless modified and there was an example in a Saxo I read about, built up by a well known company, where the valves did rub and the company blamed the customer supplied pistons, having blatantly not done a basic dry build check to see what the clearance was like!
Here are some pics from a TU5JP4 engine sent to me last year with those pistons and rods. I centre punched through the guides to do a basic radius check and there wasn't enough clearance for the standard inlet and exhaust valves. To illustrate it to his supplier, I took this pic, which shows 65.5mm across the pocket edges (easier to pic than the radius); the valve size (31.3 std) plus the centres (35.0mm) equals 66.3 without any clearance added, so even without the transfer punching you can see it's machined wrong! The intruder is too tall as well and touches the chamber on an unskimmed head:
The rod problems are harder to illustrate, but all of these rods feature an acute stress point on the rod bolt counterbore:
That's where they always fail and I've seen the same with DP rods supplied by Cat cams recently too. People often blame the bolts, but if they've bent before breaking and the rod bore edges are diverging, it's obviously cap failure and that point on the counterbore is where it starts. Also both of those rods mentioned in the TU have excessive material in the H-section, which causes them to clash with the bottom of the bore, demanding clearance to be machined, which relaxes the block in that area causing bore distortion.
In many cases people get away with it, but if you're serious about the engines your building, it's not acceptable and for the money they're charged out at, it's shocking.
daveyboy
Posted 30th Mar 2013 at 16:00
