Tale of the Crossflow

[bball7754]

After close to 45,000 miles and many track days, my Crossflow was in need of a refresh. I spoke to a known Formula Ford engine builder (30 years experience), who was willing to do the job.

 

The spec on my engine was some head work, Hepolite cast pistons, Kent 244 Cam, double valve springs, and roller rockers. It’s the “150 hp” spec.

The only thing I knew I wanted was to upgrade to forged pistons. He recommended I replace my crank with the SCCA SCAT crank. While not as robust as a forged crank, it was about a third of the price and would allow me to confidently move my redline from 6500 to 7000-7200 rpm.

 

Pistons were ordered from Burton’s in the UK, along with a new set of springs. Main bearings were replaced, the block bored and honed, some cleanup of the head work, rebuild the carbs – fairly basic stuff. Cam was in good shape, so that went back in. Replaced the clutch, which I sent to him and he balanced the crank/flywheel/clutch as a unit. Also brought the compression ratio up from around 9.5 to 10.4.

 

He called me when it was finished, and was both happy and surprised that it made 157 hp at 7200 rpm.

 

Dyno run.pdf

 

https://picasaweb.google.com/lh/photo/fwVqNSWYLVDXoTLED1fIDnM5pEeHaNF-jFxcQZ5j3uY?feat=directlink

 

Fast forward (skipping over fixing my leaking transmission) to the NJMP track weekend. At this point I had about a grand total of one hour of road time on the engine. First session starts, and I’m excited. The car feels lighter, and it’s still pulling at the end of the main straight as I get to 7000 rpm. This is going to be a great weekend!

 

As I’m coming down the main straight at the end of my 5th lap, the engine seems to go “soft”. Through turn one, and it seems to be missing a bit. Then it’s missing more, then it’s really running like crap, now I have steam coming out from under the bonnet. I limp towards the pits, kill the engine on the pit entry, and coast toward where we’re all parked.

 

I take the bonnet off, and there is coolant all over the place. The coolant catch tank is completely full, and clearly had overflowed. I also notice that there is coolant dripping out of the exhaust. I call my engine builder and we have a long discussion. He thinks I may have split a cylinder wall. Suggests I let it cool, then pull the plugs and turn it over. Which I do, and shoot a geyser of coolant out of cylinder 4.

 

Call him back, and he suggests I drain the coolant, and spray WD-40 in the cylinders and both the intake and exhaust ports. Which, again, I do.

The following Friday, I drive back to his shop with the Crossflow. He has another owner there, but he immediately pulls the head off – and here is what we found:

 

https://picasaweb.google.com/lh/photo/b9hQjWlt5MZN5sYAjqgW83M5pEeHaNF-jFxcQZ5j3uY?feat=directlink

https://picasaweb.google.com/lh/photo/BBzK1GmJ8DL34kNBK3pfdXM5pEeHaNF-jFxcQZ5j3uY?feat=directlink

https://picasaweb.google.com/lh/photo/FwTe-H96pImxnJTQC74ObHM5pEeHaNF-jFxcQZ5j3uY?feat=directlink

https://picasaweb.google.com/lh/photo/ZfpBFnggSIDhiY7qspIELXM5pEeHaNF-jFxcQZ5j3uY?feat=directlink

 

Which is not what he expected. Now, the blown head gasket and subsequent coolant in the cylinders are a symptom, but not the cause.

Conjecture has centered on overheating, but to be honest I’m not sold. I had borrowed a camera and microphone from Croc, but unfortunately the sound is distant at best. If you turn the sound up all the way, though, you can hear the engine. My first 5 laps are here – jump to 9 minutes 30 seconds to skip me getting into the Seven, wandering around the paddock, and sitting in line:

 

http://youtu.be/OFXx0S3UucM

 

There is a tinkling/pinging sound whenever the engine is under load. And the temp gauge (right gauge of the center two) sits around 80-85 centigrade the whole time. So, maybe timing? A really bad tank of gas? Both?

 

Here is the lap where it all went south:

 

http://youtu.be/Rv679Jb7UFc

 

About the only good news in all this is that the cylinders cleaned up, and another rebore wasn’t necessary. It should be all back together in the next week or two, but not knowing why the pistons melted has me real nervous.

 

Steve

Dyno run.pdf

Edited July 21, 2013 by bball7754

[powderbrake]

Steve:

it seems that the only luck you have been having is bad luck. Hang in there, it's bound to change to good luck.

 

You are fast becoming an expert in all things rotating or reciprocating on a Caterham.

[scannon]

Steve,

 

Those pistons don't look melted, they look broken. My guess is enough coolant got into that cylinder to essentially hydrolock it for one compression stroke it breaking out the sides of the piston near the valve reliefs. Were any of the rods bent? How about bent valves, those pieces of the piston probably went out the exhaust valves and likely bent one.

[bball7754]

No bent rods or valves. There also was no evidence on the valves of them being hit by pieces of the piston. I didn't show all the pictures, but the pistons on cylinders 1 and 2 were also damaged in the same way, although not as extensively. And those cylinders were dry - no coolant in them.

 

There was quite a crowd at his shop that day, including his next door neighbor who I believe now holds the land speed record in whatever class an Audi A4 would be in. Think he's making over 1,000 hp out of the Audi 4 banger.

 

Anyway, everyone was pretty mystified. But because there was no shrapnel damage, they were characterizing the pistons as having melted.

 

And when all is said and done, the only real change to the tune was upping the compression ratio. Same cam, same valves, miminal additional porting of the head, same distributor and curve. So, really didn't expect this.

 

Jerry - now you know why I haven't returned the engine hoist.

Edited July 22, 2013 by bball7754

[slomove]

.....the only real change to the tune was upping the compression ratio............... same distributor and curve.......

 

Well, sorry if I point out the obvious. But assuming the timing was optimal or even borderline before, could the increase in compression have taken the engine over the pinging edge?

[JimmyHilton]

Fuel quantity required could also have increased at the higher revs. Lean condition?

[bball7754]

Timing is still what I'm thinking, but he said total advance was 35-36, which should have been ok. I didn't think of the pre-rebuild tune as being that radical, so using the same total advance should have been ok - but, maybe the timing was off and it was more than that.

 

If you look at the AFR on the dyno sheet (the Dyno run PDF) it stays around 12.5, so in theory (again) not too lean. He thought he was going to need to change the jets, etc. on the Weber's, but the AFR was fine and consistent, so he left them the way they were.

[coffee break]

Excessive heat looks to be an element. How is the cooling systems condition?

[JimmyHilton]

Yes AFR does look pretty safe.

 

The 35-36 total advance is a bit more than the absolute max 34 I've been accustomed to. But that could be related to how quickly/slowly the mixture ignites. So I'd guess the fuel used could be an issue.

 

I will be very attuned to the verdict, and solution.

 

And very sorry to hear of the catastrophic failure......

[Croc]

That is not what I expected after what I saw happen at NJMP.

 

 

Maybe unrelated but what octane fuel were you running that day?

[yellowss7]

Steve, while watching the video, I focused on the temp gauge, and although the ticking noise was present while idling thru the paddock, I noticed that the temp did seem to rise while you were driving. I note that as mine usually drops a bit off the 80 mark with the additional high airflow at speed. (assuming I am right that the center guage is the temp gauge)

 

Tom

[bball7754]

Temp was normal for a track day - even after I started steaming (which I think was just the overflow tank, umm..., well, overflowing and coolant hitting the exhaust headers) the temp didn't go much over 90 c. There was one modification made to the cooling flow. There is a heater connection on the water pump and a another on the intake manifold. I don't have a heater, so the two were just connected with a length of hose. He removed the hose, and sealed both connection points. But, that's what he does on all the Formula Ford engines, and they don't have an issue with overheating.

 

And the sound on the video is hard to hear, so the tinkling sound could have been something else vibrating.

 

Octane should have been 93 - but that was one theory thrown around the shop that day. Bad tank of gas - maybe filled with the wrong octane, so could have been running with 87.

 

What worries me (and my engine builder) the most is that there hasn't been any kind of definitive explanation. So, it's currently being rebuilt just as it was the first time.

[Kitcat]

The engine sounds thrashy the whole time to me, even from the start. It's not the deep barritone X-flow rasp. Probly just the mic placement. Any reason to suspect the temp gauge is off?

 

Anyhow, deep condolences, stuff like this drains you mentally as much as financially.

[bball7754]

As far as I know, the sender/temp gauge are fine. However, the sender is high in the block, and apparently if the coolant is turning to steam, the steam will generate a "normal" temp. That's why the builder is sticking with the overheating theory.

 

But the coolant overflow is from the same area, and if coolant was rushing into the overflow tank, than I wouldn't think that the sensor was reading steam.

 

Zetec conversion is looking better all the time - hindsight being 20/20.

[centerfireman]

I have read on several occasions (but have no proof) that removing a heater and plugging the lines MAY cause problems with uneven coolant flow. I believe that the theory is that, with a heater and its lines in place (even if the heater is off), coolant will flow through the block differently than if the heater hoses are capped off. Some people have suggested (again, without proof) that it is better to connect the in-flow and out-flow ports in the block with a hose, to maintain the original flow pattern (as if there was still a heater in place).

[xflow7]

I've wondered about this. My crossflow (supersprint spec) has the heater path blocked off. I've seen that some people put a bypass in place of the heater core and wondered about the ramifications.

 

On first blush it would seem to me that having just a hose bypass could actually worsen cooling because you're replacing a path that provides some (albeit small) cooling capacity of its own (from the heater core) with a low-restriction path that offers no cooling capacity. Whereas, with the heater core connections blanked off, you increase the mass flow through the main radiator which should (in principle) replace some of the lost cooling capacity. I suppose if the engine is operating well within the thermostat's range, then the thermo should just open more to compensate. But, I've never seen any kind of true back-to-back comparison done. It would be really interesting to put a bypass in with a flow control valve and run a few tests with various levels of restriction.

 

bball7754, any clues from the plugs in terms of discoloration and/or damage on the insulators or electrodes?

 

Dave

Edited July 22, 2013 by xflow7

[centerfireman]

I think the theory is (again, with no proof) that with the heater passages capped off, there could be areas within the block that are "dead spots" with little, or reduced, flow. With a hose connecting the in and out-flow ports for the heater, coolant flow should be the same as if the heater was in place.

[TheDingo8MyBaby]

Here's another possibility:

 

Your car was dyno'd at 29.92 in Hg. According to wunderground, the barometric pressure was a bit higher on June 22:

 

http://www.wunderground.com/history/airport/KMIV/2013/6/22/DailyHistory.html?req_city=NA&req_state=NA&req_statename=NA

 

More pressure means more air. More air means more fuel required. It's tough to say if that could have caused your problem, but since you likely want reliability over all out power, I would consider richer mains if I were you.

 

The other thing I would consider is different pistons and a different head gasket. Where your pistons failed is the thinnest part. CP makes really nice forged pistons. CP can make custom pistons and can change the shape so you don't have such a thin area. Cometric also makes excellent gaskets and I recommend them over Fel-pro.

Edited July 22, 2013 by TheDingo8MyBaby

[xflow7]

I think the theory is (again, with no proof) that with the heater passages capped off, there could be areas within the block that are "dead spots" with little, or reduced, flow. With a hose connecting the in and out-flow ports for the heater, coolant flow should be the same as if the heater was in place.

 

Seems plausible, depending on how the coolant passages in the head are arranged.

 

Anyway, on a semi-related note and maybe more on topic, I think I've heard of cases of air pockets being trapped in the head after a coolant fill causing hotspots. When I refill my coolant, I open the plug in the intake manifold until I see coolant coming out just to make sure there isn't a bubble stuck in there somewhere.

 

Dave

[Hettric]

I don't want to hijack this thread, But I am ignorant of these matters and would like to learn. I am very surprised the pictured piston tops are counter bored to clear the valves but there are hard 90* edges and no chamfer to the counterbores. As I say I don't know what the norm is, but this is counter-intuitive to me for flow, heat "risers" and the very thin outside wall. Maybe someone could direct me to info on this.

Thanks