DT125R ARCHIVE

craigbulmer · Guru

RE: P.Valve FAIL!.

satelliteone · DTR Senior Member

malc i thort that the timmings were done by the shape n the size ot the cut outs. not the PV. All i know is that the PV closes down exhaust flow, restrict and cause back pressure. Which is ideal for tourqe. as the revs come up the port opens and lifts the restriction. The shock wave is then fully exploited.

And today

my second engine starts its new life!

PJ engineered crank! and a 1990 bottom end (case) waiting for bearings!

-- Edited by satelliteone on Wednesday 14th of April 2010 10:53:30 AM

Malc · DTR Senior Member

satelliteone wrote:
malc i thort that the timmings were done by the shape n the size ot the cut outs. not the PV. All i know is that the PV closes down exhaust flow, restrict and cause back pressure. Which is ideal for tourqe. as the revs come up the port opens and lifts the restriction. The shock wave is then fully exploited.

And today

my second engine starts its new life!

PJ engineered crank! and a 1990 bottom end (case) waiting for bearings!

-- Edited by satelliteone on Wednesday 14th of April 2010 10:53:30 AM

We are probably speaking different "timings" here... at low revs the exhaust port opens later in the cycle due to the PV closing off the top of the port than it does at high revs - the power valve doesn't restrict exhaust gas flow at all, it changes when the port opens on the downstroke.

But it's difficult when we don't/can't use exact terminologies to describe the process, so I've attached a ****ty drawing to try to make it more obvious what I'm trying to say. When ports open and close are sometimes referred to as "timings". Hope this makes more sense?

-- Edited by Malc on Wednesday 14th of April 2010 03:56:09 PM

satelliteone · DTR Senior Member

i think i know hat ya mean... its the close ness to the top of the exhaust port by the PV. moves away at higher revs and open it up. even tho the PV does not seal compression.. it must be a very crude way of changing the timming.. hot gasses hitting the PV n all that..

I see the 4 stroke way.. and to get your head around the 2T way is quite hard to do.

delve91 · DTR Senior Member

hey is that my spare bottom end (1990) if so i am told it only had 300 miles on from new!!! :o :o Guy bought the bike brand new, was in a front ened shunt and he didnt have insurance or funds to repair so left it in a barn for 19 years! haha

satelliteone · DTR Senior Member

the crank was foooobar tho..i think the crank was out of another delv.. didnt u have the good crank in the other engine..

delve91 · DTR Senior Member

I nicked the crank out of the one uve got there ;0

satelliteone · DTR Senior Member

weird, just poopped the old crank seals out, there was screw driver marks in the alloy where they have been popped out before. odd for a 300 mile engine. But then again the gearbox looks in v good shape. I will caliper the clutch friction plates see how much wear i seen in them.

Got another crank to go in 50 quid on ebay, only done 3400 miles or so. 2006 model it came out of. Got new seals n main bearings too. Happy days.. this engine will be like new. Top end will be new too. 57.65mm piston. high compression head. :)

delve91 · DTR Senior Member

yeh i took those seals out then put them back in again haha

craigbulmer · Guru

I think this is happening to mine!!!!

While idling, my bike has a funny rattle. Its not piston slap, cuz ive had slap b4. Its not 2 stroke noise cuz its a different kind of noise. Its not f'd small end bearing, cuz my mates bike up the road has a f'd bearing and its completely different. It defo coming from the top end, screwdriver on the cylinder and ear on the other end told me that.
Once you rev the bike up to 3-4ish thousand the rattle COMPLETELY stopped, just smooooooth.

I had the p/v pulley off, i noticed the pulley was vibrating, i rev it abit and as the valve turned, the rattle stopped. Also the pulley stopped vibrating, so i pinned the powervalve fully open, gave her a start and its smooth, only the slight 2 stroke noise and thats it. No rattling.

SO

Me thinks the piston is tapping the powervalve. So im gonna leave it pinned for a while until i have the parts and time to pull it apart.

Also theres a black deposit/crap in the powervalve pulley casing so i think the gaskets have gone anyway!

-- Edited by craigbulmer on Saturday 17th of April 2010 04:49:12 PM

carl13671 · DTR Senior Member

Alright craig,
mine does that too.
if i undo the cables and turn the valve it starts knocking/tapping and vibrating asthough its hitting the piston.
Is yours making a metallicy knocking noise??.

craigbulmer · Guru

kinda yeah, its frecking annoying!!!

sounds like the piston has done 1000000 miles and it absolutely shagged.

Now its so smooth sounding. If i could cruise at low revs i would keep it pinned. But you cant so i wont lol.

Went out for a hoon with the PV pinned, bloody gives it some life!!!! flippin annoying though....

satelliteone · DTR Senior Member

have both your engines been rebored in the past? new piston n rings n all that? and now u got the rattle.

not good is it. NO R&D have been done on the P.V when u go over standard. U think that my Piston was 56.5mm, thats 0.5 mill over bore and then went bang. Alan my m8 looked at his 57.9mm rebore, THe PV hits the piston, not the rings. even worse.

the only way i can do to over comes this, is a modified PV valve to cover the popular over bore sizes. I cant find anywhere that does this. Ive done my own of course as a fix. But its taking way too much metal off the back of the PV, and in the long term going to cause problems.

The other way, was to change the direction of the PV, swap the cables. This will move the PV away from the piston and not towards. Worth a try maybe.

woll · Guru

personally im not sure on this, could their be a different problem causing the p/v to hit the piston and the rings. I just can't see why such a successful motorcycle manufacturer could overlook a problem like that. Surely they wouuld have run tests on the engine, reboring it etc. to find problems like this? I've never heard of it happening before, i know quite a few people that have had dts (it's surprising how many bikers have had one) they've never heard of it. i will ask in scamaha dealers next time i go in, i know they do work on quite a lot of dts im sure if its a common problem they would have come across it before.

satelliteone · DTR Senior Member

if can woll, need some real experienced info m8..

what ya need is a overbored barrel, like 57.00mm plus, slide half the PV in and see for your self. and the rotate it so that its in the idle position. move the piston up the barrel, with the rings on. you wont see much of a gap m8.

hate to think what it would be like on a 58mm piston.

craigbulmer · Guru

I just dont know. Annoying. I dont think yammy would have overlooked this but now mines pinned theres no noise at all. It must have been hitting the powervalve.
Mines at 57mm now, so mm closer to the powervalve.

Satone, what do you mean? taking metal off the back of the powervalve wouldnt have done anything would it?

fray · Guru

I have this rattle aswell and my piston is 2mm oversize so my bore is 58mm. Ive had a whole new top end and rebore so its not that.

When i get my head back from being skimmed and my bike back running ill pin the PV open aswell and see if the rattle stops.

craigbulmer · Guru

Fray you have only had 2 rebores same as me so yours should only be 57mm?

fray · Guru

I found out that the barrel was at 57.15mm when i bought the bike. I know this coz 57.15 is stamped on the cylinder and the piston they removed which i asked for back has got 57.15 stamped on it aswell.

They then sent it away for a rebore and fitted a new piston etc. When i removed the head the other day coz the gasket was leaking i noticed 2.00 on the top of the new piston so pressumed that ment a 2mm oversize piston (58mm barrel).

Also the bloke at PJME where i took my head for the skim said the engine has had a bad seizeure in the past!!

-- Edited by fray on Sunday 18th of April 2010 06:33:14 PM

craigbulmer · Guru

yeah it sounds it tbh!! 0.5 every time, mines had 2 normal rebores so its 57mm. Yours must have been bad because its the equivalent of 4 rebores! your barrel is on its last legs, yammy say they can only have 4 rebores. 58mm.

carl13671 · DTR Senior Member

Mine was done to 57.25 and its a diffent bike,still running it in now.
Although it had a knock before which has now gone alot quieter,i can still feel it vibrate through the valve so i filed it back abit and its still the same and now ive got a good 1mm between the piston and valve.
Craig PM me your email address and i will send you a video i made of the noise before it was rebored.
Mine sounded like a muck spreader.

satelliteone · DTR Senior Member

the second cookoo clock is now put toghter. Brand new bottom end. Feels well nice n tight. give it 500 miles and thats gona be one well nice sweet engine.
New main bearings/seals, Crank with less that 3K miles on it. Engine 300 Miles on it.

next is the top end to do. nother 50 quid and its done. Barrel to 57.65mm n honed and piston kit.

craigbulmer · Guru

proper mans kitchen ftw.

satelliteone · DTR Senior Member

here is a some new pix of the standard PV with an over bored 57.65 piston and the after modded PV.

standard PV

Modded PV

oringinal 56.00 piston on top of a 57.65mm

Now, question is

would u run a standard PV on an over bore?

fray · Guru

**** that looks tight at 57.65mm imagine what mine is like with a 58mm piston :-0

Looks like us lot with the oversize pistons have a little work to do checking our pistons!

-- Edited by fray on Wednesday 12th of May 2010 03:48:07 PM

satelliteone · DTR Senior Member

its a beeatch to get the PV just right tho..a bench grinder and a dremmel. i have taken off a good 1mm from the back side of the PV. also.. the edges, not as easy as it looks as u got to get the profile correct,

The the feeder guages 39 thou (1mm) allowing for expansion. (piston rings - PV ) DIY PV modding all good..lol

least i know that the rings aint going to meet the PV now, even when she is red hot!.

fray · Guru

Think im just gonna check mine first see how close it is before i start doing anything!

fray · Guru

I pinned my PV in the open position and i still had the rattle at idle and low revs????

Dickhead · Nonce

how many miles ur engine got on it ?

fray · Guru

11,250 mate. New piston, rebore,rings and little end bearings are 1,150 miles old.