Basket Cases

[tat ty]

Perhaps I should focus on Davids Kerosene method... Very unlikely to drink anything that is BLUE.

[Phil 850]

Doh! of course you're right Phil, A 2 banger is a different fish-kettle. It would be down to bore and stroke calc to get the swept volume.
But it's still a good way to measure head volume, so useful for establishing comp ratio.

Using your method of measuring “capacity” at TDC allows for the dome of the top of the piston and the volume created by the cylinder head gasket (for those engines that have them) and the head volume.
Certainly takes all of the calculations/estimates out of it.
Then simply use the bore area x stroke for the swept volume.

[Jools]

Yep. And I don't use kero because unlike water, kero could dilute the oil sealing the piston rings.

[David Lahey]

Perhaps I should focus on Davids Kerosene method... Very unlikely to drink anything that is BLUE.

[JC1]

I took an eBay punt with this recently. Hasn't arrived from the US yet. Seller described it as a TY250 head which it obviously is not.

My guess is an early DT250 head with a decompressor fitted into a second plug hole. The decompressor may be the answer when my legs say no.

We do have an XL250 manual valve lifter fitted to the TL250 and it makes for much easier starting.

I reckon David will know what it is.

I'm a bit late on this but I think you'll find it's an MX250B/YZ250C head which were very low profile as the pipe went right across the front of the bike above the head. The DT250B/C had cutout fins on RHS for the pipe while the DT250D/E/F and IT250D/E had cutout fins on LHS. These were quite a bit taller in profile than the MXB/YZC heads (ie taller fins)

Looks like it has been fitted to a TY engine but C.R. will be higher

[tat ty]

Thanks JC1.

I should image, conditional that I've not drunk too much of David's kerosine, a lesser volume in the decompressor head than the existing will mean increased compression ratio.

If it's a marginal percentage I won't be too concerned.

Was intended to be a future project but perhaps the gauntlet has been thrown down.

[tat ty]

s-l400.png (120.06 KiB) Viewed 1496 times

Mind you, I have managed to find what looks like a pretty impressive clutch decompressor dodah to suit 7/8" bars, so that's one issue out of the way.

[JC1]

David the open class Bultaco MX bikes all had twin plug heads. Even the El Bandito. They were all 60mm stroke until the MK 9 which had a 64mm stroke to make it a 370. They got 360cc by using an 85mm bore with a 60mm stroke. I know of a MK 10 370 that I am working on at the moment which has what looks like a standard up pipe on it and has a Gem reed valve so I think it is a US one just before the MK 11`s came out. It has a strange left side cover on it which is completely different to the MK 11 ones. :Bultaco: :Bultaco: :Bultaco:

Graham, the LHS sidecover is from the M180 Frontera 250 (and maybe M181 370 Frontera) which in some markets had a battery in the airbox and the sidecover was squared on the top LH corner to make room for it. That allows a bit of room for the up-pipe too on that bike you pictured.

[Bully fanatic]

That makes sense John. Cool. Just ordered some new mudguards for it from In Motion. 95 pounds postage because the mudguards take up heaps of room.

[JC1]

Is it Michael's bike, Graham?
I have an M180 LH sidecover in the shed. I might try and post a pic of it