valve sizes on my 400

Taffy · May 29, 2004

i measured the old valves that i pulled out the other day. i don't have 30/27 but 34/27. a pleasant suprise

so if anyone else wants to check their post '01 and let me know?

this means that the husey runs 1mm smaller on the inlet and the exhaust than the 450 KTM. probably their 400 had the same but i can't get the info.

KTM has a bigger midrange hit than mine and i don't think it'll be the 1mm inlet! will possibly be the cam but also i think it could be the exhaust valves being too small. there's a kind of laymans rule that the inlet and exhaust didn't ought to be more than 5-6mm apart.

so i may look at increasing the exhausts from 27 to 29/30mm.

any comments?

Taffy

LINEAWEAVER · May 29, 2004

Hi Taffy,

KTM 450 Exhaust Valve Specifications:
Head Diameter: 1.181" (30 mm / same as 470 and up Husaberg)
Stem Diameter: .2352" (.0002" larger than OEM Husaberg)
Overall Length: 3.810" (.005" Shorter Than OEM Husaberg)

Use OEM Husaberg 501 Exhaust Valves. Better yet install one piece stainless steel Pro-Flo valves.

FYI:
Pre 2001 350 / 400 engines use a 30 / 27 valve combination.
According to the Husaberg parts manual post 2000 400 engines have a different part number from that of pre 2001 design. However, it is also stated that the post 2001 valves are applicable to all 350 - 400 models.
I suspect the larger valve diameters are intended as retrofit items for the earlier models. This would indeed make sense as in late 2000 Kenny and I did test a big valve 400 head for Husaberg.

Hope this helps.

Kind Regards,
Dale

Taffy · May 30, 2004

thanks again dale. and welcome advice.

Taffy

Taffy · Jun 1, 2004

dale

the inlet is 35mm-1mm more than i said, good job i didn't get a used 501 head after all!

i'd also say the exhaust port isn't antwhere near 100% of valve size.

i did some measurements for ya, (inlet) but don't know if they're what you might be interested in;
top of valve above alloy head base = 39.3mm
cap fitted w/ both cotters. gap twixt cap and spring base (metal 1mm) 34.4mm
spring is 39.8-40.3mm high (min/max)
so the spring is compressed 5.4-5.9mm.
valve seat widths are 37mm inlet and 30mm exhaust

inlet valve diameters 35mm means my 'tuliped' valves had lost 1.5mm width!!!!!!!! exhaust is as said - 27mm

regards

Taffy

LINEAWEAVER · Jun 1, 2004

Hi Taffy,
35 mm inlet valves makes sense as that is what we had tested in 2000.

Your installed spring height is .035" greater than that of intended OEM.
(ie roughly a 10 lb decrease in seat pressure)

Hope this helps.

Kind Regards,
Dale

Taffy · Jun 1, 2004

Dale

i just re-calculated my maths to 5.4-5.9mm compression of spring, i don't know from which figure you took your reading. i should have measured the valve stem exposure from guide before i sent the head in. blame too many years with desmo heads for that.

as .035" is nearly 1mm do you recommend i get a a washer of said width and fit under the spring base? i think that you do.

Taffy

LINEAWEAVER · Jun 1, 2004

Hi Taffy,
I do indeed adjust installed spring height to 1.320" (33.53 mm) using spring seat shims.
Dale

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