Cylinder Compressions? - SV650.org

24-03-11, 07:12 PM

Just a quick question about compression.

I know the manual says something like compression should be between 156-213 or around those, but what is the performance difference between running both at 156 or both at 213?

Second question: If running at 150, is this an issue?

Cheers!

24-03-11, 09:12 PM

213 is standard compression and what it should be, both cylinders should also be within 28psi of each other. Did you hold the throttle open fully? 150 is very low.

156 is the service limit, engine would need a overhaul.

Sid Squid · 24-03-11, 11:10 PM

In practice an engine will run acceptably with low compressions as long as there isn't too great a difference between the cylinders. What will likely be noticed is raised consumption of both oil and fuel, as long as the level of consumption is within what you find acceptable you could continue to run the engine.

However if the engine is running well and the consumption hasn't risen to a great degree I'd look at what Beabert said above - was the test done with the throttle wide? If not then the figures will be significantly reduced.

24-03-11, 11:28 PM

Throttle was wide open.

I bought a pig with the intention of learning some more (I'm not 100% with rebuilding/messing about with bikes)

The idea is to learn as much as possible. The spark plugs did like pretty black when taken out. There is no service history with the bike. I assume this could mean piston rings gone which could account for both of the above?

embee · 25-03-11, 12:39 AM

For the geeks among us, this article is one of the best comprehensive guides to compression testing I've come across.

25-03-11, 01:18 AM

Quote:

Originally Posted by embee

For the geeks among us, this article is one of the best comprehensive guides to compression testing I've come across.

Excellent thanks. Some more compression testing on the way me thinks.

25-03-11, 05:20 AM

drop bit of oil in the bores, see if it increases.

25-03-11, 07:20 AM

Also check the valve clearances. It could be the shims are too large and the valves aren't seating correctly, causing compression to leak.

I had an FZr400 thatw as a swine to start because of this and its a much easier fix than new piston rings.

C

24-03-11, 07:12 PM	#1
EssexDave Guest Posts: n/a	Cylinder Compressions? Just a quick question about compression. I know the manual says something like compression should be between 156-213 or around those, but what is the performance difference between running both at 156 or both at 213? Second question: If running at 150, is this an issue? Cheers!

24-03-11, 09:12 PM	#2
beabert Guest Posts: n/a	Re: Cylinder Compression 213 is standard compression and what it should be, both cylinders should also be within 28psi of each other. Did you hold the throttle open fully? 150 is very low. 156 is the service limit, engine would need a overhaul. Last edited by beabert; 24-03-11 at 09:15 PM.

24-03-11, 11:10 PM	#3
Sid Squid No, I don't lend tools. Mega Poster Join Date: Jul 2003 Location: Skunk Works, Nth London Posts: 8,680	Re: Cylinder Compression In practice an engine will run acceptably with low compressions as long as there isn't too great a difference between the cylinders. What will likely be noticed is raised consumption of both oil and fuel, as long as the level of consumption is within what you find acceptable you could continue to run the engine. However if the engine is running well and the consumption hasn't risen to a great degree I'd look at what Beabert said above - was the test done with the throttle wide? If not then the figures will be significantly reduced. __________________ If an SV650 has a flat tyre in the forest and no-one is there to blow it up, how long will it be 'til someone posts that the reg/rec is duff and the world will end unless a CBR unit is fitted? A little bit of knowledge = a dangerous thing. "a deathless anthem of nuclear-strength romantic angst"

24-03-11, 11:28 PM	#4
EssexDave Guest Posts: n/a	Re: Cylinder Compressions? Throttle was wide open. I bought a pig with the intention of learning some more (I'm not 100% with rebuilding/messing about with bikes) The idea is to learn as much as possible. The spark plugs did like pretty black when taken out. There is no service history with the bike. I assume this could mean piston rings gone which could account for both of the above?

25-03-11, 12:39 AM	#5
embee Member Mega Poster Join Date: Jul 2003 Location: Warwickshire Posts: 2,804	Re: Cylinder Compressions? For the geeks among us, this article is one of the best comprehensive guides to compression testing I've come across. __________________ "Artificial Intelligence is no match for natural stupidity"

25-03-11, 05:20 AM	#7
beabert Guest Posts: n/a	Re: Cylinder Compressions? drop bit of oil in the bores, see if it increases.

25-03-11, 07:20 AM	#8
Berlin Guest Posts: n/a	Re: Cylinder Compressions? Also check the valve clearances. It could be the shims are too large and the valves aren't seating correctly, causing compression to leak. I had an FZr400 thatw as a swine to start because of this and its a much easier fix than new piston rings. C

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