psi or kpa

cwalkin · Dec 28, 2006

can anyone tell me what psi or kpa should be at or between when doing hecking compression.
and should i do hot or cold?

thanks guys!

05 fe450e

sparks · Dec 30, 2006

Compression should be done when the engine is hot, pressure wise you want to be looking at 175 195 psi. Anything below 150 you have got problems.

Regards

Sparks.
www.uk-motoplat.com

cwalkin · Dec 30, 2006

cheers mate,,,,,thanks for reply

Does it make a difference from kickstarter to electric start?

logjump · Dec 30, 2006

I'm not sure how you would do an accurate compression test. Seems like the auto-decompression device on the cam would keep you from getting the accurate reading you're after.

Maybe a leak-down test would be more appropriate.

log

sparks · Dec 31, 2006

The auto decompresser would have to be deactivated and also perform this test with the throttle fully open.

Regards

Sparks.

Husabergler · Dec 31, 2006

Fresh 03 400 engine,115 psi off kick, nothing disconected, throttle closed.

Cheers, Ryan

sparks · Dec 31, 2006

But to get a true compression reading you need the complete swept volume this would mean disconnecting the decompresser and throttle wide open.

The 115psi shows that the decompresser is working but with it disconnected you still could have low compression. Surely there must be a way of disconnecting the auto decompresser unless it works like the Sherco on centrifugal speed.

Regards

Sparks.

Johnf3 · Dec 31, 2006

sparks said:
But to get a true compression reading you need the complete swept volume this would mean disconnecting the decompresser and throttle wide open.

The 115psi shows that the decompresser is working but with it disconnected you still could have low compression. Surely there must be a way of disconnecting the auto decompresser unless it works like the Sherco on centrifugal speed.

Regards

Sparks.

On a KTM, you can back the tappet adjuster screws on the exhaust side out one full turn. This will not allow the auto decomp to function. You then will get a true reading for compression.

I would assume the Husaberg would work the same way, given the similarities.

Husabergler · Dec 31, 2006

I just figured for a quick check the 115 lbs with everything as normal would be a reference point or a determining factor to look further .
I like the loosen the tappet idea, check compression at valve adjustment intervals.

Taffy · Dec 31, 2006

i disagree john, sorry!

but if you loosen a tappet by 1mm you just got rid of the valve timing by a considerable amount.

then again, disconnecting the three decomps isn't easy either!.

i think dale once quoted 175PSI.

regards

Taffy

Johnf3 · Dec 31, 2006

Taffy said:
i disagree john, sorry!

but if you loosen a tappet by 1mm you just got rid of the valve timing by a considerable amount.

then again, disconnecting the three decomps isn't easy either!.

i think dale once quoted 175PSI.

regards

Taffy

Yes, it will affect the valve timing, but not enough to skew the numbers for a compression test. Maybe a 1/2 turn would be enough. I know that even slightly loose exhaust valves begin to defeat the decomp. mechanism, manifested by (physically) hard starting, either kick or e-start.

cwalkin · Dec 31, 2006

I tried with kickstart but all i could manage to get a reading of around 90 psi,,,,(cold) without adjusting exhaust valves

the bike feels great now as i found that my exhaust vaves were very tight causing starting and riding issues..

when i get a chance i will get motor warm and looses exhaust valves and give it another shot(kick & thumber)

LeFrog · Jan 1, 2007

What tool do you use to measure that? (Just curious, still learning!)

Taffy · Jan 2, 2007

check out the term compression tester froggy!

a gauge with a 4" long nec k is forced into the plug hole and held there by hand. it has a rubber cone on the end to help keep the compression seal. the gauge fluctuates up and down wildly with every stroke but a bumper records by pushing a needle further and further the high point of the compression.

basically you bleed any previous tests out by pressing a button and then you go again. try it two maybe three times per cylinder. it's a lot easier to spot a weak cylinder on a multicylinder bike so we have to rely on the figures gained by others in 'good' tests.

it's best that the motor spins fast on the leccy boot as nothing can escape past the rings and valves. that's why 'kick' comp testing is a sod!

i suggest a rolling road might be the next best place to try. plenty of bike race shops use them!

regards

Taffy

cwalkin · Jan 2, 2007

if i use the electric start does it initiate the auto decompression on it?

Taffy · Jan 2, 2007

of course!

why wouldn't it? it doesn't know the difference between a comp test and turning over for starting!

i've known people to put the bike in gearand turn the engines backwards. i don't have auto or kickstart decomp so i'm ok.

for some older bikes here, even deactivating the auto decomp will leave the kickstart mechanism pressing the exhaust rocker and decomping the engine that way!

one of the few ways is to remove the top of the cover and find a way of holding the decomp 'bar' in the starting position so that it doesn't activate.

you can usually tell if an engine is struggling by feel and sound so that's why you won't find a dealer coming to your rescue here. they sinply wouldn't bother trying to do the test.

regards

Taffy

psi or kpa

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