detuning ?

goatman · Oct 16, 2007

Hello - it seems that a few people at various times throughout the various threads I have read have brought up the issue of detuning the engine a little to try and reduce the strain on the main bearings. I haven't been able to find a thread where anyone has really answered this question.

I have an 05 fs650e (arriving soon) which I want to try and lower the compression on. Is there a thicker base gasket available , or should I have a piston reshaped ?

If I fit the Joe Cooler oil cooler , will this reduce the oil pressure to the top end ? If I fit a more simple cooler like the one found on my old Ducati, are there issues such as pooling of the oil when you shut it down ? Are there any other options other than the Joe Cooler ?

And disconnect the TPS right ?

I realize this isn't a very popular idea here where people are very passionate about these bikes and their 100% ness , but I have come across quite a few instances where people have brought it up but have been ignored. So there is interest in giving up some performance to hopefully get some reliability.

Thanks for the great site !

whosahberg · Oct 17, 2007

if you want the main bearings to last .. don't over rev and change the oil .

if you study the design of the motor you will find something missing ... yep it's the base gasket . you remove the rocker cover , cylinder head assy . then you will split the motor .

the oil cooler is a good idea .

clean the air filter of course .

you are right about the TPS

you dont have to give up performance for reliability , just really maintain the bike .

have the main bearing end float measured so you know where you're at .

nsman · Oct 17, 2007

The relationship between high static compression,heat and main bearing life may be very real.
Lineaweaver has suggested that it is best to remove material from the combustion chamber than the piston and/or gasket area. He also suggests a longer duration camshaft is helpful.
There are many who buy a Husaberg for qualities other than its race ready engine and as such may well benifit from a slightly detuned engine.Husaberg has addressed this issue in the form of the 380 kit for the 450 engine.
If you choose to lower your compression first check your compession ratio by measuring the volume of your cylinder and head with light oil with piston at BTC and then measure the volume at TDC.Divide the numbers and and see if they are what is speced. calculate and remove small amounts of material from the combustion chamber untill you see the numbers you want.
Benifits s/b easier starting,less heat production,less sensitive to fuel quality,less sensitve to carb jetting and hopefully longer main bearing life.The down side is you will have less power and torque.

goatman · Oct 17, 2007

Thanks for that - and no base gasket - I really should have had a look at the design ! But even if I had a thicker head gasket you say there would be problems - or just that removing material from the head would be better ?

I will give this a go when it first needs to be pulled apart. It has 20 hrs on it now so hopefully it won't be too soon . I'd be happy to give up a bit of power just so I don't feel like I used to with my old RGV two stroke - listening to every noise after giving it a handfull . Still interested to know if anyone has tried adapting an oil cooler themselves rather than buying the kit. A rally rider put the Joe Cooler type up under his seat for protection which I would prefer even if it isn't quite as efficient as in front of the radiator - which I think looks clumsy on such an elegant design.

Anyway, thanks again for the help !

Taffy · Oct 17, 2007

i think dale also pointed out that you can create more heat by lowering the compression in the WRONG way. to remove say - 1mm from the piston will mean that you lose your squish area around the circumference. so that means the ignition timing is out and the engine becomes inefficient.

get a quality plug, keep the revs down but don't lug it.

personally i think it'll make your riding 'goofy' so forget about it and ride.

regards

Taffy

goatman · Oct 17, 2007

Well thanks Taffy ! A decent plug - you mean iridium ? How does that help reliability ? I've just never thought of it.

I'm not too stressed about it now - but if it does go pop I'll surely try to get it to last longer next time. It's a double edged sword this knowledge stuff - but thanks anyway !

nsman · Oct 17, 2007

goatman,
I have been contemplating lowering the cr on a FX650 i have.I found that the total volume of the cylinder and head was 711 cc and the volume at tdc was 67cc.I was surprised to see that the piston did not come to the top of the sleeve.The volume at the top of the cylinder was 15cc,the head gasket (1.5) mm was 12cc and the cyl head volume was 40cc.these # gave me a ratio of 10:6 to 1,not 11:8 as the specs say it should be.maybe if they are out one way they can error the other and yours is too high and as such is worth checking.
As you can see by the numbers a very little bit of material can greatly effect the ratio.1 mm off the piston crown would work out to 3.14 x 40 x1=5 cc(r=100-20 squish=80x.5=40)and would lower the cr to 9.8 in this fx engine.67+5=72 div 711=9.8...although a xr650r is something like 8.3!!!
Its been a while but i recall measuring the piston crown and thinking that it was not so thick as I would want to spin a mm off it, or anything, for that matter.
as soon as I can get some updated rockers i will continue with this build,I may still lower the CR,i intend to take it from the combustion chamber if I do and will let you know how it works.....cheers

goatman · Oct 17, 2007

Thanks - it seems that it's not as simple as my old air cooled Ducati which I can buy a couple of different pistons for depending on what compression ratio I want. Removing metal from the combustion chamber is something I'll have to get someone else to do, but if it is the only way I will.

I'm surprised that more people aren't that interested in oil coolers/ raised oil volumes . Maybe there is an oil cooler forum somewhere !!

detuning ?

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