Compression tester.

[Sister Sledge]

Can anyone recommend a half decent but not too expensive compression tester for my bike?
Bike uses a DRZ 400 engine. The spark plug is in the top middle of the head and deep down a narrow tube. No cooling fins as water cooled. No dimensions as yet because tank isn't off - was simply hoping someone with the same engine can point at a suitable one.
Cheers!
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CCM 404 DS

[Tankie]

Whatever you choose should be as short as possible, the longer the hose/pipe the more inaccurate the reading, this is because of the small volume of a lot of bike cylinders.
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Always learning, everyday is a school day

[Sister Sledge]

[Triton Thrasher]

[stevo as b4]

You don't need to know the exact true reading based on no volume in the tester or the adapter tube/fittings. It does not matter or make any difference to how your DRZ engine will run if the tester shows - 10psi or so over the quoted book figure. Remember two identical DRZ engines won't likely give the same readings, due to tolerances and other factors.

The compression tester is an indicative diagnostic comparison tool, nothing more. If you have any tester of any level of accuracy, then all that matters is comparison readings of previous test results and the current one over a fair mileage or or running hours interval.

It's the same story with leak down testers, and even endoscopes (the current favourite catch all diagnostic tool). None of them alone used once will tell you how healthy your engine is, and what is wrong with it with total certainty. People these days seem to obsess over diagnosis and what's wrong, rather then periodic engine maintenance and overhaul.

A Moto Gp team doesn't want to faff around measuring compression and leak down or looking down a scope to tell them how good the condition of their engine is, or when to re-build it. They will have logged running hours, and components will be life'd according to the engine design and development team, and the usage conditions and environment. When the stipulated running hours or mileage is achieved, then that motor is coming out regardless.

Bit off topic, but hopefully it shows the insignificance of doing a one time random compression test on a perceived good engine, and worrying about the N'th psi reading and trapped volume in the tester.

[Sister Sledge]

I hadn't realised they had the one way valve right down like that. Thanks.

I want my own for exactly that reason - to watch things. The engine is older, will have had abuse and I know they're considered bulletproof but still - having a tester to hand would help keep an eye on things.
Mileage is 42k miles btw.
The tester will be handy for future machines too.
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CCM 404 DS

[Robby]

I have a compression tester, somewhere. I've used it twice in nearly 20 years.

Any problem that causes a loss of compression is a big problem. Most of the time the reason is that someone was working on the bike without knowing what they were doing, and cocked up valves or timing.

Otherwise, you only lose compression because your rings are shot or your valves aren't closing. Shot rings only happens if you have a million miles on the engine or have run it without any oil in the engine at some point. Valves not closing used to be down to carbon deposits, in the 1950s.

You'll cause more trouble that it's worth. Either use the tester wrong, get a low reading and panic, or cock up fitting the spark plug back in and break it. Just service it normally and ride it.

[stevo as b4]

I have to agree with Robby here.

Sure I've tested old suspected worn down on power engines, and found low 70-90psi readings (indicated). But I knew that the motor was old, smokey, had lots of clanking or piston and bearing wear and in some cases serious clonking end float in the crankshaft. It didn't take a genius to realise the motor was knackered.

But most times I've had a well running bike that's had a compression affecting engine issue, it's gone suddenly from having good compression to suddenly having virtually none at all, and each time this was due to catastrophic engine failure that you wouldn't need any special tools or instruments to diagnose.

Maybe the above makes me sound like a ham fisted clueless engine wrecker, but I'm not honestly! I've now learnt that the wise people and the knowledgeable people are the ones that do periodic engine overhauls while they are still running relatively well. It's far cheaper to take apart and re-assemble well running engines, than non running ones that look like the internals or cases have been attacked with a sledge hammer.

[Sister Sledge]

OK I'm going to take on the advice given. Always worth asking folk with direct experience like that.

I'll save the money for a fun time with something probably illegal.
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CCM 404 DS

[Triton Thrasher]

The real purpose of the tester is to boast that your compression is higher than somebody else’s.
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Rrrrrrrrrrrrrrrrrr