PC2000 powervalve question

[Trxjim]

Guys,

I bought a used PC2000 powervalve top end here last year and I am having a little trouble with it. I am burning up pistons in it a little too often in my opinion. Any advice on making this top end live a little longer? It currently has a 68mm wiseco pistion (260cc) and a 21cc dome. I have a 88 bottom end with a long rod crank with the typical spacer plate at the bottom of the cylinder. Now I am getting 240 psi on the compression tester which seems a little high for this setup. I run 110 octane sunaco fuel. I am having the cylinder sent of to be bored out (69.5mm) and recoated. I think that I am also going to ceramic coat the piston, exhast port, and head when finished. After spending this money I really don't want it to melt down. Thinking about lowering the compression, probably need to cc top end and blueprint motor a little better. Any advice dealing with these top ends would be appreciated.

[312R1]

Post up some pic's of it and I'll help you out...if there put together right.. there hard to beat.

[Burns310r]

We need to see pictures of the failed pistons.

How many hours are you getting out of them?

What carb, and jets are you running?

What oil and oil mixture are you running?

[KM250R-BDTM]

Originally posted by Trxjim
Guys,

I bought a used PC2000 powervalve top end here last year and I am having a little trouble with it. I am burning up pistons in it a little too often in my opinion. Any advice on making this top end live a little longer? It currently has a 68mm wiseco pistion (260cc) and a 21cc dome. I have a 88 bottom end with a long rod crank with the typical spacer plate at the bottom of the cylinder. Now I am getting 240 psi on the compression tester which seems a little high for this setup. I run 110 octane sunaco fuel. I am having the cylinder sent of to be bored out (69.5mm) and recoated. I think that I am also going to ceramic coat the piston, exhast port, and head when finished. After spending this money I really don't want it to melt down. Thinking about lowering the compression, probably need to cc top end and blueprint motor a little better. Any advice dealing with these top ends would be appreciated.

Hate to see anyone burn down pistons, you need to lower compression to 195-205 LBS, these cylinders are set to run at no more than 210 LBS. 110 Race Fuel is only useable to 13/1 UCCR, at 240 LBS you are way above 13/1 and in the 16/1 range. Lower to 195-205 LBS with 110 Race Fuel, check your UCCR, and determine the compression allowed for your particular set-up on 110 Race Fuel. Remember 110 race Fuel is not really 110 Octane, it is in the 106-107 range.

[89trx250r]

The DR. has spoken haha :)

[Trxjim]

I am running a 38mm A/S carb
50 on the pilot jet
168 on the main

BR9 plugs

Maxima 927 caster 32:1

Plugs usually look pretty good, golden brown to a little black

Hard to tell how long they have lasted. Maybe one or two weekends in the dunes and maybe 4 or 5 trips to the mx track. I take care of it, but run it hard when I do.

[Trxjim]

another

[Trxjim]

I removed the top ring, It was in while it ran.

[Trxjim]

As you can see its getting too hot on the exhast side. No detonation and the plug looks ok. I am wondering if the exhast flange is causing me problems. Duncan says to not use an aluminum one and of course I use it anyways. Stock steel flange is going back on. These cyclinders don't have a lot of cooling jacket around the exhast port with the powervalve taking up space. I am also really curious why my compression is so high. This motor was originally set up by Baldwin motor sports, I believe it say's dustin royer on the side. It has a 21cc dome 86 style of piston and spacer plate. Maybe I need a new compression gauge but I have got these readings with two gauges. I will problably look into calculating out the compression ratio.

btw, I have been using an LRD exhast but have a duncan on the way. Also use a boysen rad valve.

[mohler]

compression gauges dont usally lie on the high side its normally on the low side. the jetting will depend on your Evaluation from sea level. i have a 275cc duncan power valve and your jetting doesnt seem close to what i have. but im not sure dont remember. i usally get a whole XC season out of my pistons

[wild250rman]

If you have the original piston look to see if the dome was milled some are sete up for port timing that way maybe contact baldwin with the info on the cyhlinder for best info. I use to run a ct pro x cylinder set up that way I rebuilt it without the milled piston dome and it pushed way to much compression.

[mx91a]

Cranking PSI numbers can be a misleading way of determining fuel requirements, especially on a powervalve engine. Don't forget as RPMs rise so does the PV blade, increasing port duration and lowering the CCR which lets the engine rev out better. I remember checking the compression on a KTM 300 engine many years ago and it was cranking about 240 pounds and oh yeah ran on pump gas!

Are you running a YZ, ATC or TRX piston?

[C-LEIGH RACING]

Get you something to scribe a line, on top of the piston direct over top of the machining edge in front of the wrist pin hole.
The straight up & down edge on the side.

Now sit the cylinder back on the cases & check the scribed line on the piston top in relation to the aux exhaust port edge.

I would bet, you have some port linking going on between the machining on the side of the piston & the main transfer ports & it is causing stagnant crankcase charge leaning the engine out.
A 168 main, is mighty lean if your thinking the engine is running hot around the exhaust area.
Neil

[machwon]

As mentioned before, it sounds like you have too much compression. 240 is way to high and 21cc dome would be too small if the squish was set right. Duncan would likely never sell a motor with over 200. Does the dome have a number that matches the cylinder number?

[89trx250r]

Yeah No Offense but when I typed the DR. Has spoken at the start of the thread, its because THE DR. just told you exactly what was wrong...AND you chose to ignore that... Anytime you see BDTM or C-LEIGH post BOTH of them Are IMO the DR.'s of our quads you should take everything they say very seriously...

[mx91a]

21cc dome might not be the problem my LRD MX 265 OEM cylinder (68.75mm bore) has a 20cc dome and cranked 230 psi and I just bought an engine with a pro-x 260 powervalve cylinder and it has a 21cc dome, pretty much the same setup as your PC2000 with a 68mm bore. I haven't put the gauge on that one though. Do as suggested before check your squish clearance to make sure it is .040-.060". Also Dr. Neil's advice about the port linking and main jet should be followed he is the 250R guru!

[C-LEIGH RACING]

Now I dont claim to be a guru, just know what my hands have touched & let not leave out everybodys elses thoughts, because I have been wrong at times.

Best thing, is if you know they were or are a Mac Dizzy member to look at what they are saying.

That port linking deal, is something I've been battling with on Pro-x cylinders for quite a while.
I've tryed to get the machining changed on either the cylinder sleeves or on the piston itself & not had any luck yet from CT or LA Sleeve.
looking at the pics, looks like the Duncan cylinders have the same problem.

Now for the fix,
Eddie Sanders Racing has listened has a new piston, that is machined different the will stop the port linking. It is still a Wiseco piston, but has a different part number than normal & machining around the wrist pin area is different.
He has all sizes from the 310 up to the 420cc.
Neil

[250r4life]

who did you buy that cylinder from?

I sold a 68MM Duncan powervalve top end on here a few years ago and in talking to Duncan i thought they said they had only custom made a few at 68mm for a handful of people.

[KM250R-BDTM]

Neil has a good point on the cross-linking of the exhaust to transfer ports on some of the BB cylinders.

However; the OP said this was a PC2000 with a Wiseco 68MM piston. Wiseco has been making 66MM to 69.50MM piston kits for the 250R to prevent cross-linking for many years.

On the PC2000 cross linking with a Wiseco piston kit is not an issue. The 2 auxiliary exhaust exhaust ports do not meet with the piston wrist pin relief, hence; no cross-linking.

While this is a question best answered by the manufacture of the PC2000 cylinder kit, I would bet they never intended this cylinder to be run with compression above 205 PSI...call them and ask them; get a clear answer to the question.

[312R1]

Originally posted by KM250R-BDTM
Neil has a good point on the cross-linking of the exhaust to transfer ports on some of the BB cylinders.

However; the OP said this was a PC2000 with a Wiseco 68MM piston. Wiseco has been making 66MM to 69.50MM piston kits for the 250R to prevent cross-linking for many years.

On the PC2000 cross linking with a Wiseco piston kit is not an issue. The 2 auxiliary exhaust exhaust ports do not meet with the piston wrist pin relief, hence; no cross-linking.

While this is a question best answered by the manufacture of the PC2000 cylinder kit, I would bet they never intended this cylinder to be run with compression above 205 PSI...call them and ask them; get a clear answer to the question.


When Loren built my 275cc PC2000 he set it up with 210 PSI..Runs like a raped ape.;)

[Trxjim]

Originally posted by C-LEIGH RACING
Now I dont claim to be a guru, just know what my hands have touched & let not leave out everybodys elses thoughts, because I have been wrong at times.

Best thing, is if you know they were or are a Mac Dizzy member to look at what they are saying.

That port linking deal, is something I've been battling with on Pro-x cylinders for quite a while.
I've tryed to get the machining changed on either the cylinder sleeves or on the piston itself & not had any luck yet from CT or LA Sleeve.
looking at the pics, looks like the Duncan cylinders have the same problem.

Now for the fix,
Eddie Sanders Racing has listened has a new piston, that is machined different the will stop the port linking. It is still a Wiseco piston, but has a different part number than normal & machining around the wrist pin area is different.
He has all sizes from the 310 up to the 420cc.
Neil


Neil, I think we are all tinkers. That part of the reason we love these machines. As an engineer I like understand how things work. I think it is amazing me how simple these machines are and yet I never fully understand them. I appreciate your help and will look into the port linking issue.

[Trxjim]

Originally posted by 250r4life
who did you buy that cylinder from?

I sold a 68MM Duncan powervalve top end on here a few years ago and in talking to Duncan i thought they said they had only custom made a few at 68mm for a handful of people.

I bought it on here a year or so ago, cant remember who It came from. I wondered about te 68mm piston also. I assumed that Baldwin had it replated a little thicker. That may make more sense though. Its soon to be 69.5. Cant wait.

[250r4life]

I use to run the Wiseco 68MM racers choice piston in mine and it worked well. If I recall correctly they only made the Racers Choice piston in like 2 sizes- 68MM being one of them.

I also ordered a different dome for mine to lower the compression as well.

[machwon]

Originally posted by KM250R-BDTM
While this is a question best answered by the manufacture of the PC2000 cylinder kit, I would bet they never intended this cylinder to be run with compression above 205 PSI...call them and ask them; get a clear answer to the question. [/B]

Again, this is good advice. Look at what I was saying before, all the parts numbers on the cylinder, dome and spacer if included should MATCH. Otherwise someone has compromised the original set up.

TRXJim, don't forget to ask yourself (or the DR's as some peoples call them) what happens when you go from 68 to 69.5mm bore. How much higher is the compression now? Was the dome cut for a 68 or a 69.5 bore? When you have a nicasil liner Duncan would make a very specific cut dome.

For the doubters, yes I was a dizzy member before they charged for membership. I do around 50 motor builds a year, so far this year a 4mm banshee, prox310, 2 370's and a mini 90 have been shipped. a new esr310, and 50, 70 and 90cc mini's are works in progress. micro sprint 250 will be back for dyno tuning in a couple weeks and a scooter motor from the Bahamas is coming my way today. Just saying, I've also had a few cylinders come through my shop...

[C-LEIGH RACING]

We would love to have you back at Mac dizzy Machwon.
Things have really change there & lot of old member are back.
Quite a few more mini folks on as well.
Neil