Ducati Sporting Club UK > DesmoDue Race Series > DesmoDue - General Questions and Chat > Lack of acceleration possible Eng swap

[Lee M]

I have noticed that my class B monster is lacking acceleration along the straights. At Cadwell "Stafford" was making approx 30 meters on both straights on a 600ss.
On a track day this at Snetterton the same thing happened with another 600ss who was running standard road sprockets and I had a 15 toothed front sprocket and 48 toothed rear sprocket, so should have had the extra get up and go.

I am going to carry out a compression test and then if the results are near 10.7:1
I will chuck it on a dyno to see the power output.

Hopefully this will this will tell me if the lack of acceleration is down to the engine or my fat arse?
So my question is:-
1) Can anyone help with the lack of power?
2) Ithought about buying an engine and overhauling it for the future, can anyone tell me if a 600ss engine will fit in my monster frame.
3) Has anyone an engine for sale

Thanks in advance for any help.
Lee

[dunlop0_1]

Basic stuff like a valve regrind, valve clearances and belt tension will have a positive effect. Carb set up and a dyno run are a must really but you also need to get the gearing right and get out of the corners right. Yes the SS engine will fit.

[Lee M]

So today I carried out a compression test, engine warm, throttle fully open and assuming the valve clearance is correct; the results are as follows:-
Front Cyl - 100-105 psi bouncing dry and 122 psi wet
Rear Cyl - 115 psi dry and 125 psi wet

As the book compression ratio is 10.7:1, assuming atmospheric pressure is 14.7 psi I take it is just a case of multiplying 10.7 by 14.7 equalling 157 psi or there abouts.

If this is correct the front cylinder is losing 57 psi overall made up from:-
157 – 122 = 35 psi from the valves and 122 – 100 = 22 psi from the rings and the rear cylinder is losing 42 psi overall , 157 – 125 = 32 psi from the valves and 125 – 115 = 10 psi from the rings

Or looking at it another way the front cylinder is working at 63% and the rear at 73% giving me an overall engine performance of 68%.

Bad news for the engine but at least I can keep eating pies and drinking ale.

What to do now?

[dunlop0_1]

Lost compression could just be poorly adjusted valve clearances (closers could be too tight). I would allow for some piston/bore wear but removing the heads and re seating the valves and adjusting the clearances correctly will pay dividends and not cost very much.

[Lee M]

Yep, I suppose that would be the way forward to bring both cylinders up by over 30 psi each. My concern is the piston losses; 10 psi on the rear is on the edge of acceptable but 22 psi from the front is a little large.
I suppose if I take the cylinder heads off I can sort them out and look at the pistons at the same time.
Can the cylinder heads be removed with the engine in the frame?

[skidlids]

Leak down test needed

[Lee M]

Can you please explain a "leak down test"?

[skidlids]

You pressurise the cylinder on The compressions stroke with both valves closed using compressed air through a leak down tester that contains a pressure regulator and a couple of gauges, the difference in the gauges then tells you your losses.
Any leaks can often be heard either by listening to the end of the exhaust or the airbox inlet or the crankcase breather

[Lee M]

Rings a bell, I will look in to it.
Thanks

[skidlids]

one of these
http://www.ffx.co.uk/tools/product/S...oJwwo dsF4A8w

maybe a local garage has one