z-ya Posted May 6, 2011 Author Share Posted May 6, 2011 This is the lash pad that broke: There are no grooves like this OEM one: This is what Dave Rebello was referring to. With this groove, it give the lash pad a weak spot where it can break. He has never seen one snap like this when there wasn't a groove. This is a full competition head with spring pressures to match. I'm also running slightly less lift than what it ran with in the day. If there were valve float we would have known it way before this happened (going on 1.5 days of tuning). The rocker that came off took out the one next to it. The valves look straight, and the springs are in tact. I will pressurize the cylinder to see if the valves are leaking. Thanks, Pete Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 7, 2011 Share Posted May 7, 2011 Valve float? What's that? Seriously, we haven't floated the Bonneville engine yet... Someone would have to use a very unstable cam profile to make an L-Valvetrain float! Quote Link to comment Share on other sites More sharing options...
johnc Posted May 7, 2011 Share Posted May 7, 2011 Valve float? What's that? Seriously, we haven't floated the Bonneville engine yet... Someone would have to use a very unstable cam profile to make an L-Valvetrain float! Or worn stock springs on a ITS 2.4L engine. At Cal Speedway and a couple Buttonwillow configurations you have to run that engine over 7,300 rpm for a time. After a race weekend you see a 5% drop in valve spring pressure on the stock springs from doing that. The next race weekend you will only see 7,150 rpm before the engine flattens out. Keep pushing it and you won't be able to go over 7,000 by the end of the weekend. If you don't replace the valve springs you'll bend a valve the following race weekend on one of your heroic pass efforts at the end of the longest straight. Ask me how I know that. Quote Link to comment Share on other sites More sharing options...
z-ya Posted May 7, 2011 Author Share Posted May 7, 2011 Pulled the head today. No piston damage. I'm having my machinist check the guides and spring pressures again on that cylinder (#2). Stay tuned... Quote Link to comment Share on other sites More sharing options...
Cobra_Tim Posted May 9, 2011 Share Posted May 9, 2011 Or worn stock springs on a ITS 2.4L engine. At Cal Speedway and a couple Buttonwillow configurations you have to run that engine over 7,300 rpm for a time. After a race weekend you see a 5% drop in valve spring pressure on the stock springs from doing that. The next race weekend you will only see 7,150 rpm before the engine flattens out. Keep pushing it and you won't be able to go over 7,000 by the end of the weekend. If you don't replace the valve springs you'll bend a valve the following race weekend on one of your heroic pass efforts at the end of the longest straight. Ask me how I know that. Ditto... Been there and done that... not too fun Quote Link to comment Share on other sites More sharing options...
SKiddell Posted May 11, 2011 Share Posted May 11, 2011 Z-Ya Out of curiosity, how deep are your retainers and what thickness pads are you running I have seen a pad "skew" in a shallow retainer. Quote Link to comment Share on other sites More sharing options...
Tony D Posted May 11, 2011 Share Posted May 11, 2011 We ran Isky springs, and changed them every so often. But we weren't running 7300rpms either. Well, maybe that's when the cam started pulling hard! Quote Link to comment Share on other sites More sharing options...
z-ya Posted May 13, 2011 Author Share Posted May 13, 2011 Z-Ya Out of curiosity, how deep are your retainers and what thickness pads are you running I have seen a pad "skew" in a shallow retainer. They are pretty deep steel retainers: ~0.170" lash pads give a good wipe pattern with the cam I'm using. Quote Link to comment Share on other sites More sharing options...
z-ya Posted May 13, 2011 Author Share Posted May 13, 2011 Here is where the rest of the car is: Scott at Ballistic Motorsports is doing the exhaust for us. Quote Link to comment Share on other sites More sharing options...
Leon Posted May 13, 2011 Share Posted May 13, 2011 I've been excitedly following your build and don't remember if you mentioned what you're doing for the exhaust. Out of curiosity, what are your exhaust specs if you don't mind sharing? Quote Link to comment Share on other sites More sharing options...
z-ya Posted May 13, 2011 Author Share Posted May 13, 2011 I've been excitedly following your build and don't remember if you mentioned what you're doing for the exhaust. Out of curiosity, what are your exhaust specs if you don't mind sharing? We are running a Datsun competition style 6-3-2 header with dual 2-1/4 pipes to either Magnaflow glass packs and straight pipes exiting out the center, or megaphones. We will be able to swap the glass packs for Megaphones at tracks that allow those sound levels. Kind of like this: Quote Link to comment Share on other sites More sharing options...
Leon Posted May 13, 2011 Share Posted May 13, 2011 We are running a Datsun competition style 6-3-2 header with dual 2-1/4 pipes to either Magnaflow glass packs and straight pipes exiting out the center, or megaphones. We will be able to swap the glass packs for Megaphones at tracks that allow those sound levels. Kind of like this: Nice, that is going to sound amazing! I love the sound of twice pipes on these engines. Quote Link to comment Share on other sites More sharing options...
TimZ Posted May 13, 2011 Share Posted May 13, 2011 Valve float? What's that? Seriously, we haven't floated the Bonneville engine yet... Someone would have to use a very unstable cam profile to make an L-Valvetrain float! Understood - I was more pointing out that in my case this was caused by the rocker coming off the lash pad far enough to allow the pad to move or rotate far enough to get the ears in a bad place. Throwing out ideas as to things that might case this to happen, assuming that z-ya didn't drop a valve seat. On the theory about the high shoulders on the retainers, if this were an issue you would be seeing pretty obvious witness marks on both the retainer and the underside of the rocker, which I haven't noticed in the pics so far. Quote Link to comment Share on other sites More sharing options...
z-ya Posted May 21, 2011 Author Share Posted May 21, 2011 OK, I'm pretty certain we found the problem. You know what happens when you ASS-U-ME. All looks good with guides and valves as expected. Except, exhaust valve length is 119mm. Mmmm, 3mm longer than stock. Looking closer at the geometry when the valve is closed the surface of the rocker tip that is touching the lash pad is almost on the casting. There is barely any clearance between the retainer and the rocker. In fact some of the rockers have a little groove worn in that area. When I got the head, the cam towers were not installed, but there was a bunch of cam tower spacers in the "bad day at the track" box. I measured the stack of front shims (the only ones that are different), and it measured 0.072". The head is shaved about 0.055", and they used a stock head gasket. So I calculate that the shims should be 0.055" for stock valves. The cam towers were shimmed 0.017" more to account for the longer valves (if my assumptions are correct). I'm running a 2mm gasket, and had shimmed the cam towers 0.017" to account for the thicker gasket and head shaving. This would have been OK for stock valves. 0.025" would have been exactly correct but I didn't have the right thickness shim, so I went with a set of 0.017" shims from the stack I had. So to keep the geometry the same I should shim the towers 0.025" + 0.017" = 0.042". This make sense? Quote Link to comment Share on other sites More sharing options...
Tennesseejed Posted May 22, 2011 Share Posted May 22, 2011 (edited) This make sense? Building a race engine and noone checking the wipe pattern on the rockers? No. That doesn't make sense. Your assumption only addresses the change in distance between the crank and the cam sprocket. Your assumption doesn't account for a smaller base circle on a lumpy aftermarket cam. You are probably looking at a new cam, rockers and custom lash pads. I recently cut .050" off a N42 to go with a stage 3 cam. After shimming the cam towers, I ended up using lash pads between .175" and .254" in order to get a consistent wipe pattern close to the edge of the rocker stud side. A page back in this thread you mentioned using .170" lash pads, which I assume you meant on all cylnders. There is no way that you can shave a head, use an aftermarket cam, and be able to use .170" lash pads on every cylinder. I hope you can salvage your current cam and rockers. You have an awesome build going and I absolutely love your car. If you do end up buying new lash pads, instead of trying to buy a bunch of different sizes, consider buying them all at the tallest height you need and then having a machinist trim them down to the exact size you need. Either Xnke or 1FastZ recommended that to me and it was a really good idea. Edited May 22, 2011 by tennesseejed Quote Link to comment Share on other sites More sharing options...
z-ya Posted May 22, 2011 Author Share Posted May 22, 2011 Building a race engine and noone checking the wipe pattern on the rockers? No. That doesn't make sense. Your assumption only addresses the change in distance between the crank and the cam sprocket. Your assumption doesn't account for a smaller base circle on a lumpy aftermarket cam. You are probably looking at a new cam, rockers and custom lash pads. I recently cut .050" off a N42 to go with a stage 3 cam. After shimming the cam towers, I ended up using lash pads between .175" and .254" in order to get a consistent wipe pattern close to the edge of the rocker stud side. A page back in this thread you mentioned using .170" lash pads, which I assume you meant on all cylnders. There is no way that you can shave a head, use an aftermarket cam, and be able to use .170" lash pads on every cylinder. I hope you can salvage your current cam and rockers. You have an awesome build going and I absolutely love your car. If you do end up buying new lash pads, instead of trying to buy a bunch of different sizes, consider buying them all at the tallest height you need and then having a machinist trim them down to the exact size you need. Either Xnke or 1FastZ recommended that to me and it was a really good idea. Maybe you didn't read the entire thread? Yes, of course, I did check the wipe pattern, and a 0.170" lash pad produced a good wipe pattern on all cylinders. The cam and rockers are fine, as they survived almost 2 days on the dyno. What was wrong was the rocker arm geometry due to the fact that the head has longer than stock valves. Longer valves will allow more lift. The head was not built by me, but someone from Bob Sharp Racing. I don't have the original cam, so I had Isky grind me one.. I do have the lash pads that were run on the head. So I shimmed the cam towers another 0.034", and now the original lash pads (0.210) give a good wipe pattern on at least one valve. The geometry also looks better where the rocker meets the lash pad. Quote Link to comment Share on other sites More sharing options...
z-ya Posted June 21, 2011 Author Share Posted June 21, 2011 Engine in car, and running. Sounds nasty with the megaphones. Hope to do a practice day on the 30th. Photos of exhaust to come later. Quote Link to comment Share on other sites More sharing options...
KillerBjt Posted June 22, 2011 Share Posted June 22, 2011 (edited) Sound Clip with exhaust! Edited June 22, 2011 by KillerBjt Quote Link to comment Share on other sites More sharing options...
z-ya Posted June 25, 2011 Author Share Posted June 25, 2011 Sound Clip with exhaust! Will need lots of compression on that mic. I'll try to capture the sound. Quote Link to comment Share on other sites More sharing options...
z-ya Posted June 27, 2011 Author Share Posted June 27, 2011 More pics. Quote Link to comment Share on other sites More sharing options...
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