Engine Issue at Formula Bharat – Decompression Lever Damage

The team uses a KTM 390 as the heart of fireblade from the past 3 years. The fireblade 3.1 at
Formula Bharat 2018 was on the engine of make 2016 which was tested for around 550kms.

The team faced an engine issue at Formula Bharat 2018 during the Driver change in the endurance event. After the 1st half of the endurance the engine didn’t crank up, hence we had a DNF. But the engine did crank at the post TI, during the Intake check. The Engine system started off with the work to diagnose the issue. It was observed that the engine cranked when it is cold with CTS level indicating 3 bars or less and did not when heated. The engine also produced a significant/ noticeable sound when tried to crank. It sounded as if the starter motor was not able to move the  piston, the piston being constrained the motor just kept on drawing current with no hail. After certain attempts, the engine  completely failed to crank up. The fuel discharge, spark condition was all checked, as we got to know that there are no issues in them.

The engine was taken to a near KTM service centre and a complete overhauling of the engine was done. It was found that the decompression lever and its actuator did suffer from a small wear, due to which it became functionally inactive.

The decompression lever helps to leak out a bit of compression during the compression stroke by opening one of the exhaust valves. This compression leak in-turn decreases the load on the motor allowing it to reciprocate the piston with less effort. The wear was a part of wear that the engine undergoes during its life cycle and does not have any specific reason behind it.
As said earlier the engine did crank when it is cool and didn’t when hot was because the wear on the decompression lever started off earlier with a small pit. It actuated the decompression lever but not to its complete extent. At higher engine temperatures the load on the piston increases since the high-temperature gases inside the piston expand thermally leading to a higher overall load on the piston. The opposing load on the piston is the summation of inertial forces, frictional forces and gas pressure and the later increased at high engine temperatures.Hence due to comparatively lower compression leak and increased load on the piston the engine failed to crank up.
The life of the decompression lever cannot be determined on the basis of number of cranks or kilometers driven and hence has to be regularly checked for its pristine condition.
As we had this issue at the most crucial stage of our competition, we would like to bring this to all Formula Student Teams. Put up your issues and comments, we are open to discussions.

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Param
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Param

What was the compression in the cylinder with the decompression lever actuated and in it’s de-actuated state?

Param
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Param

Another thing I’d like to know is, what is the CCA of the battery? Because although the compression is pretty high at higher temperatures, a standard Amaron or Exide battery was enough to crank our old R6 in it’s ‘hot’ condition.

Team
Veloce Racing
Abhishek Patil
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Abhishek Patil

The compression ratio of KTM 390 is 12.6:1 but the compression leak the decomp lever was not measured or calculated.

Rujul
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Rujul

It’s great sharing such information. A good read.
So disassembling the whole cylinder head is the only method to routine check the lever? Also, are there any symptoms observable or audible before reaching this stage of lever failure?

Abhishek Patil
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Abhishek Patil

Disassembling the head ain’t a good option since you can face issues with the cylinder head sealing and also with the tightening torque of the cylinder head bolts. The other methods are, you hear a peculiar sound that the engine creates while cranking it seems as if the battery has discharged. The piston just constraints as the the starter motor simply draws current. Also you can frequently check for the battery voltage as a damaged decomp drains out the battery faster.

Alok apte
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Alok apte

You don’t need to remove the engine head as the decomp lever is on the exhaust camshaft. Simply open the valve cover check the lever and close it back again.

Kushal
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Kushal

One suggestion to all teams would be when your engine is not firing up due to some electrical or mechanical issue don’t keep on cranking the engine for long time.Find out the problem,rectify it and then crank. 1)When using a stock ECU a Ktm Engine should start within 2-3cranks,if not there’s definitely a problem.More we crank without the engine getting fired up,there is improper lubrication to the cams and other parts which lead to excessive wear than designed. 2)When using a standalone ECU number of iterations are done during initial starting and tuning phase.Even there can be a chance of… Read more »

Danish
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Danish

Regarding the master cylinder doubt the judges had during your FB 18 tech inspection, what was the step taken by the team?

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-
Subodh
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Subodh

During FB 18 tech inspection, we had a cut-section of the similar master cylinder that helped us to prove our point and convince the tech judge.

Team
Team Kratos Racing
Danish
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Danish

Did you faced any problems with the braking system since you are using only 1 master cylinder? Does all the 4 wheels lock together when the brake is actuated? Or are you using a proportionating valve in the rear lines to limit the rear pressure?

Team
-
swapnil
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swapnil

for KTM 390 rc/duke , we can use custom made radiator or stock radiator ??

Team
-
Abhishek Patil
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Abhishek Patil

Swapnil, you can use any radiator which can satisfy your needs. Not mandatory to use a stock one.

Team
Teak Kratos Racing