TimZ Posted August 21, 2007 Share Posted August 21, 2007 Well, I had alluded to it in a couple of other posts - a couple of weeks ago I had a something go south on #5 (it always seems to be #5). Got the head pulled last weekend (finally), and was puzzled for a while... At first glance, it looked like something got ingested, but the more I looked, the weirder it was - there were only marks around the intake valve, none around the exhaust, and the turbine wheel showed no signs whatsoever of anything having passed through it. Turns out what happened was that the intake valve seat came loose but was held captive by the intake valve. It got the crap beaten out of it for a while, which also held the valve open and let the lash pad move and get crushed by the rocker. Eventually it found its way "home" and the valve held it in place, since I didn't hammer it any more after it started having problems. So, it appears that this is the weak point that the higher exhaust temperatures from the GT42 uncovered - apparently this is fairly common in turboed air cooled engines where elevated head temps are more common. So, in addition to getting some new valves (with higher temp alloys), I'm going to be in need of some valve seats with higher temp capacity. I've been looking around a bit for valve seat insert suppliers, but I've not seen much for 1800 degF EGTs. Anybody got a line on a good supplier? Quote Link to comment Share on other sites More sharing options...
MONZTER Posted August 21, 2007 Share Posted August 21, 2007 Hey Tim, Got some Oversized Beryllium seats from Kameari directly. They are supposed to help transfer the heat better. Just had them installed, but not run em yet. I also got the Beryllium guides to help again to pull the heat out of the valves. Not cheap stuff, but I figured good insurance. Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted August 21, 2007 Share Posted August 21, 2007 WOW... Never seen that before! I guess at 600hp you put some..."Different" forces on an L6 head. May I ask what you are using to seal your head gasket? (red and blue stuff??) Quote Link to comment Share on other sites More sharing options...
TimZ Posted August 21, 2007 Author Share Posted August 21, 2007 May I ask what you are using to seal your head gasket? (red and blue stuff??) It was just some copper gasket seal and gasket remnants - the head gasket is the Nissan Comp one that uses separate fire rings that have machined grooves in the block. The gasket only seals the oil and water passages. Due to the difference in compressibility between the fire rings and the gasket, sometimes the gasket needs some 'help' to seal until a couple of heat cycles and re-torques have been done. Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted August 21, 2007 Share Posted August 21, 2007 Cool thanks! I figured you were using seperate fire rings. Hope you can get your valve seat problem worked out! Quote Link to comment Share on other sites More sharing options...
rags Posted August 21, 2007 Share Posted August 21, 2007 Hi Tim, Ouch. Why does higher head temps make the seat fall out? Joe Quote Link to comment Share on other sites More sharing options...
OlderThanMe Posted August 21, 2007 Share Posted August 21, 2007 Hi Tim, Ouch. Why does higher head temps make the guides fall out? Joe Pure Aluminum expands about 5% at it's critical temeperature. With such high EGT's the aluminum was getting close to it's critical melting temperature and did some expanding. Quote Link to comment Share on other sites More sharing options...
rags Posted August 21, 2007 Share Posted August 21, 2007 I thought that too but there is something that doesn't make any sense to me. The exhaust side would feel the burden of the increased temps before the intake would and it was an intake seat that fell. I'm not saying it wasn't caused by the heat I just want to understand why. Joe Quote Link to comment Share on other sites More sharing options...
Flexicoker Posted August 21, 2007 Share Posted August 21, 2007 I have no idea how much interference is required when pressing in a valve seat, but for that to happen it seems to me like it was a machining error rather than a defective valve seat, ie. too little interference. Quote Link to comment Share on other sites More sharing options...
johnc Posted August 21, 2007 Share Posted August 21, 2007 Had that happen to the cylinder 5 in the ROD but the seat blew apart and I found most of it in the intake manifold. The cause was very slight detonation in that cylinder. What caused the detonation was a localized hot spot in the cylinder. This is a well known issue for high cylinder pressure L6 engines. What cured the problem for my car was increasing the cooling system pressure to 28 psi to reduce nucleate boiling at that point. Quote Link to comment Share on other sites More sharing options...
Z-Gad Posted August 21, 2007 Share Posted August 21, 2007 Spoke with my engine builder this morning, and he echoed the Beryllium seats, as they have a higher copper content and will dissipate heat better than your average seat. A asked him if "pinning" the seat was necessary, and he said that as long as it was machined properly, it was not necessary... He also asked about your cooling lines for the rear of the engine, as those cylinders tend to run the hottest being the furthest away from the water pump... Mike Quote Link to comment Share on other sites More sharing options...
TimZ Posted August 21, 2007 Author Share Posted August 21, 2007 I thought that too but there is something that doesn't make any sense to me. The exhaust side would feel the burden of the increased temps before the intake would and it was an intake guide that fell. I'm not saying it wasn't caused by the heat I just want to understand why. Joe Yep - this has occurred to me, too. Those seats have been in there for quite some time, so I'm thinking the added temps just kind of put the seat over the edge. At the same time, I'd rather not have a similar failure in the future, so if I'm replacing the seats anyway, I'd prefer not to under spec things. There isn't any obvious evidence of detonation, but it's most likely unrealistic to assume that it never happened - I'm running a bit higher cooling system pressure than stock - 18psi as I recall. Perhaps I'll start a separate thread on that subject. My builder had the beryllium seat idea too - I'll research that bit more, but aren't there wear issues associated with those? Quote Link to comment Share on other sites More sharing options...
thehelix112 Posted August 21, 2007 Share Posted August 21, 2007 http://www.delwestusa.com/manufactured/valve_seat_inserts.asp Support your local. Dave Quote Link to comment Share on other sites More sharing options...
MONZTER Posted August 21, 2007 Share Posted August 21, 2007 Quote Link to comment Share on other sites More sharing options...
rags Posted August 21, 2007 Share Posted August 21, 2007 So if Nissan did the same thing that Del West did, the alloy's used for Intake and Exhaust seats will be different and the Exhaust seat will transfer heat better than the Intake. That could explain why the Intake seats come loose. Joe Quote Link to comment Share on other sites More sharing options...
Administrators BRAAP Posted August 21, 2007 Administrators Share Posted August 21, 2007 Seen this same scenario many times with the old OE bronze intake seats in the pre ’76 heads, though usually when the seat falls out, it wedges itself and holds the valve open enough for the pistons to contact the valves and subsequent massive damage is the result. Oversize OD valve seats will be needed. Monzter, Just curious why Beryllium copper seats in the intake and not the exhaust? Chambers look real nice BTW, shaped similar to our chambers, nice work. Quote Link to comment Share on other sites More sharing options...
MONZTER Posted August 21, 2007 Share Posted August 21, 2007 Hi Braap, Why on the intake only? That’s the only way I found them. I got them from the Kameari guys in Japan, and that was the only way they sold them. I did not know where else to get them except by going custom. Maybe some other application would have fit, but I had no clue where to find this info. I was thinking it was because of a durability thing with the exhaust valve? and the hardness of the seat material? - just a guess. The head was done by Rebello. Dave got the head flow 212 at 25" .5 lift intake and 150 at 25" .5 exhaust. He said he spent way more time on the exhaust than the intakes. I'm hoping it will run pretty good. Jeff Quote Link to comment Share on other sites More sharing options...
TimZ Posted August 22, 2007 Author Share Posted August 22, 2007 Talked a bit more with Ferrea today, and they referred me to these guys: http://cheprecision.com/html/seats.html Interesting use of copper alloys for better heat dissipation -they recommended going to a wider, deeper seat for more contact area, both for heat transfer to the head and from the valve. Next, I'll need to see just how much deeper I can go. Quote Link to comment Share on other sites More sharing options...
speeder Posted August 22, 2007 Share Posted August 22, 2007 Same thing happened to me several years ago - #5, dropped intake seat, pounded back into place with only minor scarring of the piston. We redid all the seats in that head with some kind of upgraded parts that my machinist found (don't remember what kind) and it was good for as long as I used that head. Interesting stuff about cooling.... Quote Link to comment Share on other sites More sharing options...
Daeron Posted August 22, 2007 Share Posted August 22, 2007 I guess at 600hp you put some..."Different" forces on an L6 head. QUOTE OF THE DAY!!!! EDIT While I'm at it: Monzter, what head casting is that, P series? Quote Link to comment Share on other sites More sharing options...
Recommended Posts
Join the conversation
You can post now and register later. If you have an account, sign in now to post with your account.