rm

My Feedback: (27)

I've got a 175 that was running great, but started leaking fuel all over the engine compartment. So I replaced all the gaskets, O rings, and did the bearings, also sanded down the valve cover to get a better seal.

Now I've got a problem. It won't go over 6400 rpm with a 20x10.5 apc. I'm running a YS glow plug, non cdi. At 2 turns open it dies when I run up the throttle. At 1.5 turns it will run at the 6400 and leaves a lake of fuel exhaust on the field bench. Anything less then 1.5 turns and the rpm drops off. Didn't notice any heat problem as I could hold my finger on the head without it scorching me. Cowl was off at the time.

What I did at the field.........
replaced all fuel lines on motor
cked tappets
run a new fuel line straight from tank to motor
switched to a new jug of fuel

Still could only get 6400. Flew it for a short flight. Didn't quit on me, but way lacking power. Pull to vertical and immediately motor started to loose rpms. This is all with the cowl off, so plenty of air flow.

Took it home and tore the motor down and did the following
flushed all carb nipples, cked orings, pulled out throttle barrel, looked to be ok
chked cam, timing looks right
pulled pump off. all springs, gaskets, diaprhram look to be ok. also flushed out through the nipples.
pulled off ck valve, flushed it, looks to be ok
redid tappets

Reassembled and ran it up. 6400 again. I'm pretty sure I should be getting more than this, but I'm at a total loss. This is just the 2nd time I've torn a ys motor down as I'm just teaching myself how to do this, I always sent them to Richard.

I'm thinking I have a pump problem, but then I have all the exhaust fuel?? Any thoughts? One thing I noticed in my research is the pump plunger I have is a straight sided barrel. According to another post and picture I saw the 175 plunger is tapered on the end, but mine isn't and is the original.

Any thoughts would be appreciated. Prob be cheaper just to send it to YS, but I'd like to learn how to handle this.

bjr_93tz

You've stated you've already checked it but I'd double check the cam timing. It's hard to do because you really should take the throttle body off to line up the dot on the crank web to the right spot so the dot on the cam is in the right spot too.

Tappet clearance is another thing I'd double check, too little you should be able to tell straight away without pulling the engine apart. You mentioned pulling the throttle barrel, I found the seal arrangement meant I could only put mine back in from the opposite side it comes out from otherwise it'd take a chunk out of the seal..

It sound's like it's getting plenty of fuel but not burning it right.

You did put the ring back on the piston after the first teardown ??

PS. Double check the disk valve in the backplate is located to the crankpin properly and not offset to either side of it. I'm not sure from memory if it's possible to have the crankpin locate to one side of it's correct slot but it's worth a look..

riot3d

Another thing you may want to check. After about 150 to 200 flights, sometime a layer of oil residue/ film can developed between the disc valve & the backplate, & the engine rpm could drop. Disassemble the disc valve from the backplate, thoroughly clean both parts with denatured alcohol. Reassemble by tightening both screws until both parts are snug with some friction - not free spinning - & it should regain some rpm.

I usually get about 6,900 to 7,100 with my 175 on 30% heli & 20 x 10.5. However, I don't think by cleaning the disc valve/ backplate will increase the engine by 500 rpm. Usually, about 200 to 300 more. If you only get 6,400, it could be cam timing or need new piston ring.

Hope this helps.

Adrian

apereira

Are you sure the valves are closing tight with no leaks?

Regards

Alejandro

Dave Harmon

I have had glow plugs leak around the seal or become loose causing a huge fuel leak as well as causing engine operation to degrade.
You might want to start the engine and observe around the plug to see if it is leaking....run at full throttle.
Or just change it and see what happens.

Also....I have had a lot of trouble with Du-Bro fuel line now that Prather is out of business and their fuel line is not available anymore.
The DB line is very soft and has silicone chips in it as well as powder or chalk to prevent it from sticking together.
Flush all lines before using them.
Also....when installing the DB fuel line....the nipple on the engine can gouge out a 'flap' on the inside of the line which flutters over the opening of the nipple causing weird operation.

UKpatternflyer

For what its worth, I get:

[TABLE="width: 585, align: left"]
[TR]
[TD]Engine
[/TD]
[TD]APC Propeller
[/TD]
[TD]Engine Speed
[/TD]
[TD]Propeller Weight
[/TD]
[/TR]
[TR]
[TD]170 CDi
[/TD]
[TD]18.1 x 11
[/TD]
[TD]7850
[/TD]
[TD]132g
[/TD]
[/TR]
[TR]
[TD]170 CDi
[/TD]
[TD]19 x 11
[/TD]
[TD]7460
[/TD]
[TD]135g
[/TD]
[/TR]
[TR]
[TD]175 CDi
[/TD]
[TD]18.1 x 11
[/TD]
[TD]8160
[/TD]
[TD]132g
[/TD]
[/TR]
[TR]
[TD]175 CDi
[/TD]
[TD]19 x 11
[/TD]
[TD]7740
[/TD]
[TD]135g
[/TD]
[/TR]
[TR]
[TD]175 CDi
[/TD]
[TD]20 x 10.5 PN
[/TD]
[TD]7500
[/TD]
[TD]158g
[/TD]
[/TR]
[TR]
[TD]175 CDi
[/TD]
[TD]20.5 x 10 PN
[/TD]
[TD]7230
[/TD]
[TD]171g
[/TD]
[/TR]
[TR]
[TD]175 CDi
[/TD]
[TD]21 x 10
[/TD]
[TD]6700
[/TD]
[TD]171g
[/TD]
[/TR]
[/TABLE]













on Optifuel 30% ULV fuel. The 175 figures were with a proto engine and I've noticed the production engines are slightly below this in performance (~200 rpm).

From my experience the assemblies that affect the power include:

Head, valve fit
Pump
Piston / ring / liner
Rear disc valve

Assuming the engine used to run ok and it isn't about to destroy its main bearing, then the CAM gear should still be in the right position, but worth checking according to the instructions. I think you should double check the fuel residue you are seeing. If it is neat fuel mixed in with whatever to make it look burnt, it might be simply a pump gasket leaking fuel at high pressure. The disc valve is a common issue and can lead to significant power loss. If the valves are carboned up then unless you know how to re-grind them a new head assembly might be needed. Sadly the only real way to check is to part swap against new or known components.

Please let us know how you get on with this.

Best wishes

Keith

riot3d

>> If the valves are carboned up then unless you know how to re-grind them a new head assembly might be needed.

Keith,

Normally, only the exhaust valve is carboned up on mine, the intake one is usually clean. I just use the back of an ex-acto blade to scrape off the carbon residue.

Adrian

apereira

Rm,

if your valves are ok, another posibility is the gasket between the crankcase and the isolator is backwards, double check on that.

regards

rm

My Feedback: (27)

Success!!!

Thank you to everyone. Turned out to be the disc valve. Mine was freely wheeling. After finally figuring out what part was being talking about, and finally figuring out how it came apart, I found a lot of fuel on the back of it. Cleaned it up, reassembled with some friction. I've disassembled and reassembled this engine so many times I no longer need the diagram. I would have never come up with this on my own.

Anyways, 1900-7200 on 30% magnum heli, and the power is back. I don't understand why this part can't be free wheeling, seems counter to everything I've thought.

Thanks again!
Robert

bjr_93tz

Thanks for reporting back.

I'm getting close to rebuild time and will double check mine as well...

kenh3497

The only way for the disc to seal is to run VERY close to the carb body. The oil film makes the final seal and of course lubricates the assembly. Without a good seal the fuel charge leaks buy and is not transferred /held in place. On my 53, I thought .001 would be a good number.... Wrong! then I tried .0005 using shim stock as a gauge....Wrong again The disc has to basically rub (very lightly) on the carb housing.

Kind of a similar thing is how the piston skirt of a 2C engine "seals" the cylinder to piston so on the down stroke there is enough"compression" to force fuel charge into the cylinder. As a former powersports mechanic we had several small bikes that had great compression above the piston (100+ psi) but ran like crap even if we did get them started. Turned out the cylinder was scored so not a good seal, no fuel transfer.

Ken

MAVROS

Just a quick question if I may

Is the disc valve supposed to have some free play when moved side to side by hand ?

rgds

Mavros

rm

My Feedback: (27)

Hey Mavros

Mine has a miniscule amount as the head of the bolt/screw is just slightly smaller than the hole of the disc. Wouldn't call it freely moving though.

apereira

Mavros,

No play at all, and the bolt should be tightened so you can turn the disc with some drag feeling.

But no play

Regards

Alejandro

MAVROS

Alejandro,

Thanks I didn't think there should be any play.......time to change the disc valve.

regds

Mavros

arnstein

My experience is that play will develop radially over time, however, does not seem to hurt the performance.
But no need to change the entire disc valve, just the Disc Valve Pin (YS part no. E1228 (170CDI)).
The reason the pin gets worn is that the disc valve is not balanced hence the pin has to react the radially forces.

regards,

Arnstein

MAVROS

Hi Arnstein,

Thanks for the advice........it turns out you can't buy the pin on its own you have to buy the whole disc valve assembly.

regards

Mavros

arnstein

Mavros,

I was not aware of that, the cost of the pin is probably only 10% compared with the complete assy. It certainly would help keeping the maintanence cost down.



regards

Arnstein

MAVROS

OH so you can ...i will try my supplier again

thanks Arntein

ps Where did you get yours?

regards

Mavros

arnstein

Directly for YS.

Arnstein

MAVROS

Which website are you using for YS

Mavros

arnstein

http://www.yspower.co.jp/en/index.html

MAVROS

Arnstein,

Thank you so much just placed an order ...much cheaper than whole assembly.

kind regards
Mavros

drac1

My Feedback: (4)

Interesting. 100's of flights and I've never had to replace this pin.

drac1

My Feedback: (4)

RC Japan are good for YS engines and parts.