XFlow woes

[OliverSedlacek]

So I've lost another camshaft on my crossflow. As before, it was the inlet lobe on number 2 cylinder. Can anyone suggest why I should be having problems with just this one lobe? The engine is dry sumped and distributorless in case that makes a difference.

[Golf Juliet Tango]

Rob Morley has found quality issues recently with the usual supplier.

He is using a different supplier now.

[revilla]

Speaking without any particular crossflow knowledge, but just some ideas ...

• Is the corresponding rocker healthy?
• Whatever method is used to support the rocker and adjust the clearance, is it holding the follower flat and at the correct angle to the camshaft?
• Valve guide clearance? Any hint that the valve may stick occasionally? Just thinking that may leave a briefly enlarged clearance so causing the cam lobe to impact the rocker rather than ramping open smoothly.

[Roger King]

Difficult to be specific, but as others have said, you need to check for anything running tight, or even pistons hitting valves.

I don't know the history of your camshaft, but when I was building Crossflows I got to the point where I put my prices up and only used brand new cams ground onto blanks in conjunction with the much more expensive competition cam followers. This worked out to be much cheaper in the long term due to lack of problems (the cheapest way to do anything is - properly). Certainly, in the late 1990s and early 2000s the quality of the normal cam followers was appalling with bad grinding and soft material. I can't comment about today, but it may still be the case.

Is the camshaft a new installation? It is important to bed an unused (either new or reprofiled) cam in at around 2500rpm for half an hour; If you are using an extreme cam profile you sometimes need to do this with inner valve springs only and then fit the outers afterwards. This process provides a bedded-in running surface with a hard skin. It is also important to make sure that the lobes and followers are extremely well lubricated before firing up fo the first time.

Because of the heavy valve gear, Crossflows have to run much stronger valve springs than more modern engines; this, coupled with the relatively small area of the cam followers means that the pressure at the cam/follower contact point is much higher than newer designs, which can cause failure.

[OliverSedlacek]

Thanks for the info Roger. I've put photos on a blog posting as that seems the easiest thing to do on this website. The cam and followers were fitted less than 4000 miles ago. The cam manufacturer explicitly gave instructions to just run the cam in using normal gentle running. The profile is around 295 degrees and the springs are VS7 with standard ratio roller rockers. With hindsight I regret not fitting a new gear to the oil pump.

Who produces cams ground from new blanks these days?

[Roger King]

Well, Kent Cams used to, but I don't have any up to date info I'm afraid. To be honest, the competition followers were more important than the new blank.

[Steve Sheldon]

I suggest you call Rob Morley at Ratrace Motorsport  01707 645040

 

[OliverSedlacek]

Dave Gemzoe has volunteered to come over and offer an expert opinion.

[OliverSedlacek]

Dave Gemzoe is a top bloke! It's amazing what you can see if you know what to look for. The verdict is that the cam wasn't hardened properly.

[Golf Juliet Tango]

I hope the replacement is better.