yeah i reccomend the conversion to everyone ..ran fine before lol

 

been reading about bad exhaust valve...that fits the symptoms, looks like i need to buy a comp tester 

https://www.youtube.com/watch?v=ysAK8fcrReI&feature=youtu.be

 

 

Edited 14 September, 20188 yr by steveo3002

Can't open the video.

 

 

 

Leak down test or vacuum gauge showing regular drop from steady 17to19inches idle to much lower would confirm a valve issue.

 

Don't buy a Silverline comp tester.

I have a Draper unit you can borrow.

 

Piece of paper held loose at exhaust pipe should have steady pushes. If sucked onto the opening that is exhaust valve burn.

 

I asked early about all exhaust gases from MOT.

I've re-found the diagnosis chart

http://crypton.co.za/Tto know/Emissions/rich_mixture.html

Hope it helps.

(or http://crypton.co.za/Tto know/Emissions/lean_mixture.html)

Edited 14 September, 20188 yr by dvderlm

 

Yes that sounds a bit odd (especially at 6 seconds).

 

Mate of mine who mends chainsaws loads a recording into Audacity and looks at the waveforms. It works for him with 2-stroke small capacity single cylinder engine. 

yeah its worse in person..the leaner i set it the worse it gets , i can get it down to 13.5-1  and leaner it stalls 

 

i think next step is a good session with carb cleaner around any potential air leaks - then a comp test when i get a tester 

Does not sound like inlet leak. It would surge and pulse when driving.

 

Play at1/4 speed and you can see the puffs if watching at fullscreen.

we will see...

 

if its valve trouble i might have them recut at a machine shop, do you know anywhere that can be trusted around here 

https://www.facebook.com/HeadRacingDevelopments

near Ely.

 

If only standard exhaust valve burnt at an edge, wouldn't you just get a replacement valve and lap it in?

 

 

think i might be an idea to have the seats recut ...i dunno lets see if its faulty first 

 

have you use those chaps yourself?   

Yes. years ago they mended a Sierra 1.8 CVH burnt valve and the engine outlasted the chassis.

 

And did my moderately big valve head with Pinto inlet valves including hand reaming the valve guides, and some shoulder porting, which has been absolutely trouble free since I  fit it over 2 years ago. 

I visited recently and got asked some useful questions for one of my crazy ideas.

 

 

If your valve seats are getting a bit wide, it may pay to have a 'three angle cut.'

The problem with wide contact areas is that the valve spring load is 'shared out' over a larger area, resulting in less gas-tight sealing.             In the case of the exhaust valve though, it has to be remembered that the only cooling that the valve gets, (apart from through the valve stem/guide) is when it is clamped to its seat, so in this respect, a slightly wider contact area is an advantage - Like most things in life then, it is a compromise.

 

Your problem still sounds to me though as if it may be due to an air leak, somewhere between the throttle body and the manifold joint with the cylinder head.

 

Like many other people, I will be very interested in what eventually turns out to be the cause of the problem. I would though, tend to 'go for' the simpler possibilities before removing the head which, even with re-worked valve seats, may not make a lot of difference.

 

Regards

yeah im not ready to pull the head just yet...agree id like a 3 angle cut if its coming apart , is this something any engine will do routinely or is it a performance thing?

 

and yes it does fit the description of an airleak too....although its a pretty basic engine , all gaskets were new , fresh inj o rings  and vac hose , im going to check it one last time with brake cleaner , then try the paper over the tailpipe trick 

Edited 16 September, 20188 yr by steveo3002

It improves flow so yes for performance, but can be done without any other porting keeping up inlet flow speed so good for economy too.

More important for inlet valves but placing the begin of 45 angle right - towards stem - can help prevent exhaust valve edge burn

 

I think they can do more than 3 angles nowadays...

http://johnmaherracing.com/tech-talk/3-angle-valve-job/

 

Dick Field at HRD mentioned he subcontracts fitting new valve inserts nowadays - I think he hasn't replaced that particular cutting machine.

had a few mins to look at it today

 

passes the paper on the tailpipe test..no sucking in

 

sprayed carb cleaner on all joints -no change

 

vac gauge hooked up...holds very steady  with a rich idle , slightest wobble at weak idle - suggests no valve trouble?

You could try using your vacuum gauge to set the ignition timing - this is especially useful when an engine is not standard, and the recommended timing may not be best suited to it.

Method: With the engine at normal temperature, advance the ignition timing to give maximum vacuum.

               Carefully note the vacuum reading.

               Retard the timing 'a fair bit'.

               Advance the timing until your vacuum gauge reads EXACTLY 1/2 inch Hg below the previous noted reading.

               Tighten the distributor - Job done.

I can't claim that doing the above will cure your problem, but for the few minuets that it will take, it is worth a try.

 

Regards

yeah ok worth a look...my gauge only reads bar will need to google that

6 hours ago, steveo3002 said:

passes the paper on the tailpipe test..no sucking in

...

vac gauge hooked up...holds very steady  with a rich idle , slightest wobble at weak idle - suggests no valve trouble?

Hooray. Definitely not burnt.

 

1 to 2 inHg (0.03 to 0.07 bar) regular drop could still be leaky valve.

https://www.onallcylinders.com/2016/03/31/vac-visual-quick-guide-vacuum-gauge-readings/

 

Steady 17 to 22  at idle (0.55 to 0.74 bar) is good

(It can be much less with big overlap cam and four open trumpets than with a shared inlet plenum  - I get about 11inHg or 0.37 bar with maybe  a 1 inHg wobble. For me that may be valve guides or valve clearance  or twincarb DHLA balance out or indeed timing. Was rock steady with the Weber The Amethyst only gives me 1 degree digital adjustments - might try twisting the dizzy for sub degree movement).

 

0.017 bar is 1/2 inHg

 

Edited 17 September, 20187 yr by dvderlm

was about -.75 bar so around 22 inches

ordered a comp tester...mad not to rule it out one way or another

 

so all plugs out and throttle wot when cranking right?

Yes.

Dry test first. 

 

Best with engine warm, start with well charged battery. You ares just comparing cylinder by cylinder, so can be done with cold engine. For me cold reads higher, I guess the bores and valve clearances are smaller when cold?. 

Disable fuel pump or injectors, definitely if you have a cat.

Place the leads where they can't spark and ignite fuel vapour (being ultra safe).

Screw in the tester tight but not too tight. Needs 14mm thread if you get a choice.

 

Crank for about 5 or 6 turns. Look at the gauge. Record it. Reset the gauge - on mine a little valve lets the air out with a satisfying whoosh. Move to next cylinder.

 

For the wet test - to check whether low comp is rings - not valves, add some clean engine oil before screwing in the test thread part. . A squirt can or tube is easiest - the spark  plug hole angle makes pouring hard I found....

and squirt can be sent at cylinder wall not piston bowl. I'm sure it soon gets distributed, but it is the rings you are trying to seal. Half a teaspoon is plenty  

 

 

 

yeah righto

 

wasnt sure the wet test would work with the dished pistons

When you reconnect everything and start it after it will smell of oil from exhaust for a bit. I've never looked what that does to lambda reading or if it could affect a cat.

yeah i dont have a cat and will run it with a blank in the sensor hole 

 

so you saw results from a squirt of oil ?  guessed it would sit in the dish?