KNOW YOUR… Valves and Valve Clearances

We caught up with Dan Miles from DMP Performance to find out everything you need to know about valve clearances, what to look for with yours and why you should pay attention to ’em…

FB: Let’s start easy! What’s the purpose of the valves?

DM: Well, they’re a vital part of an engine! Basically, the valves in the engine open and close, which then allows the fuel and air to enter the combustion chamber. As the pistons go up and down they turn the crankshaft… and you’re going!

FB: How good are standard valves?

DM: In all honesty, they’re usually pretty good – for the most part anyway. Especially on road bikes; back in the day there were a few models that had earlier intervals for checks, and the odd issue which was recalled, but they’re much better than say, off-road bikes. I mean, there are some off-road models which can need the clearances done every six or so hours!

FB: How long will they last before they need checking?

DM: To be honest, on most regular road bikes, doing road mileage and the odd trackday here and there, I’d say about 16,000km at the very most, but it obviously depends on the bike, the engine and, of course, the rider. As an example, some of the early RSVs actually

required a check at the first service, whereas other machines can actually go for a lot longer.

FB: What about on a race bike?

DM: That’s a tough one. Once again, it depends on how hard you’re riding and what bike it is, but I’d like to think people would check their clearances at least once throughout the season if they’re racing at a reasonable level full time. Obviously alongside that, I’d recommend on getting a full rebuild at the end of the year, which includes having the clearances checked. I imagine superbike teams would check theirs every few rounds.

FB: What usually goes wrong?

DM: Over time, the constant abuse of revs can mean that the valve stretches. This means that the little gaps between the top of the valve stem and the rocker arm is out of the sweet spot – so it can be open all the time, for example. This can mean everything from losing compression and making it difficult to start your bike, to eventually dropping a valve and making a right mess, so you have to be careful if you think things aren’t right.

FB: How do you know if they need checking or are going wrong?

DM: As I said, you’ll probably be able to tell if your bike isn’t starting correctly, or especially when sitting at idle, as it won’t be sitting as smooth as it should. Another big tell-tale sign is a loss of power, while it can also mean your bike drinks more fuel – it should be noticeable, but to be honest, if you don’t know your machine inside out, it can be difficult to spot sometimes.

FB: What benefits come from checking valves and valve clearances?

DM: The main thing you’ll feel is that the whole thing will be much smoother. Rather than being an imperfection in the running of the engine, everything should be nice and crisp, so your bike will fire up, sit nicely at idle, drink less fuel, and even have more power. It has its biggest effect on bikes that rev higher, so think R6s, CBR600RRs and things like that; so if you own a 600cc, especially as a race bike, it’s worth getting them looked up.

FB: How can you upgrade valves?

DM: There are loads of options on the market for upgrading valves! The main option you’ll probably see are made of steel, but in my opinion the OE stuff is always good. It’s been designed perfectly, but if you want that extra oomph performance wise, always make sure you use a recommended and reputable brand.

FB: How easy are they to check, and are some bikes more difficult than others?

DM: In all honesty, if you’re unsure about working on an engine, or if you don’t have a lot of experience in mechanics, I wouldn’t recommend it. It’s full on, open heart surgery! I’m talking tank off, cams out, timing, shims and bucket, etc. It’s not just like changing the odd spark plug, and it can go wrong quite easily. Don’t get me wrong, some are easier than others, but some can be a real pain in the ass. Take a V4 for example, especially of the Italian variety! They can take anything from six to eight hours just to get the bloody thing done, whereas an inline four would probably take about half that.

FB: Any tips for people trying it at home?

DM: Make sure you’ve got an idea of what you’re doing, a lot of time and no distractions! It can be a pain and there’s a lot of bits that have to come off, so make sure you’ve got a nice, big, clean workspace. Have your manual to hand before you start, and make sure there’re no specialist tools required for your machine. It could catch you out!