871 exhaust valve noise

[Larry B]

I have an 871 in a1977 mci5b . My knowledge of 871 is limited. I have exhaust valve noise which sounds to be on #1L. If this was a gas engine I would suspect a bad lifter.I have checked valve clearance and injector timing. This is a very recent rebuilt head from Waterous Detroit Deisel. New liners,rings and pistons I switched injector to a different hole to see if noise would move with injector. Did not move. Can any sort of compression test or air test be done on a two stroke through injector hole? Any ideas what else to check?

[robertglines1]

ck for broken spring on cam follower/push-rod.

[luvrbus]

Probably just a badly worn bridge or loose adjustment on one


good luck

[Larry B]

I checked cam fallowers, push rods not bent,and roller clearance within spec. New springs installed in case one was weak. I switched valve bridge ( had leftover  from jake install) and reset. Is there any air test that can be done through injector hole to see if valves are seating proper?

[robertglines1]

How does it run?   If they were not seating it would be running rough. has your peak rpm dropped? One other thought do you have any signs of un burned fuel- like black streaks from exhaust joints or drips out exhaust pipe? On same side?

[Larry B]

It does not run that smooth all the time. I have reworked the blower and governor.  Lets say it is idling smooth, if you bring rpm up to 1600 and let go when it come down , it will start hunting by 50 rpm about half the time. note; my engine is not in the bus at present time. It is running on shop floor to a water barrel

[robertglines1]

Sounds like you are fairly knowledgable. Probably more than I.  Will just try to give food for thought. Try checking travel of valves. Just rough measurement to make sure the two are equal on same cyl.  Do you have air box check valves/drains on engine? They should seal air box pressure around 900rpm. Did this engine have the timing gears removed during the rebuild?  Just a few thoughts. Other more knowledgable than I will chime in.  Bob

[luvrbus]

If you are asking if there is a leak down test for a 2 stroke the answer is no,go back and adjust everything again do you have a buffer switch ? installed if so remove it and check it, worn fuel control rod stands ends or worn governor linkage will cause the roll also.

Simple things like the springs installed in the wrong direction on the tubes do you have the 2 screw tubes or spring loaded 1 screw tubes.

Piston slap is not uncommon with a 71 series with old style 1 pc pistons and rods , when a wrist pin retainer turns loose it will make noise are you getting more smoke from the left side than the right ?

What setting did you use for the Jakes A timed 71 series use a different setting than a std timed engine

[Geoff]

You could have lost a valve seat-- look at the height of your valves with the bridges off and if one is noticibly higher you lost a seat.  Also, if the bridges are not set right you could have dropped a valve, but you should of noticed that by now.  It takes a special compressor test tool to check compression-- it consists of a dummy injector, hose and gauage.

[luvrbus]

You probably hit it Geoff he got the setting off and caused valve trouble I had one here the guy installed Jakes and bridges and turned the engine with the starter to do the setting and they were to tight and he bent every valve on the engine,he also he told me when I asked he did the setting on the bridges from one side only

I never turn the engine with the starter when doing overhead work you are asking for trouble if you are not careful I am not saying he did that but people do and pay a price  

good luck

[Larry B]

Thank you for all the good check points. Try to address all guestions. Buffer switch is not installed. New fuel rods and pins, eyes where worn. new thrust bearing and carrier in gov. changed pins and brass bushings on gov weights.. My engine has two pc pistons with new liners and rings. N65injectors-- advanced timing on gears I set valve bridges with.015 feeler guages so drag is even. valve clearance at 0.015 and injector at 1.484 jakes set at.064. I turned engine over with barring tool befor starting after jakes bolted on. The jakes have not been activated yet  they are in place and engine has run since jake heads bolted on. I have one screw rack adjustment Before I activate jakes I would like engine to run proper. Tomorrow I will check the items mentioned and start resetting all.

[luvrbus]

If you don't have a buffer switch or the buffer screw in the governor the engine will roll and surge did you set the starting aid and does you housing have a external starting aid adjustment or internal 

good luck

[wg4t50]

Have two thoughts;
1-IS the noise from the valve assy or could it be from something nearby, have you tried with valve cover off and at idle, use a screwdriver and see if you can change the tone of the noise by playing with the bridge, rocker assy, etc ?
2-Why use A timing on a MCI-5, assuming it is  either the 4 speed manual or auto.  With Advanced timing, the engine does not do well at the lower rpm where the 4 speed units operate,  with the 10 speed range between 1800-2500 rpm, "A" works good, not at 1400-1600 rpm

Have played both settings with the 4 speed then with the 10 speed RTO910. Then used the 12V-71, All in a MCI-7, same results.
Just wonderings from the village idiot, been there, done that etc..

[bevans6]

I just have a couple of thoughts too.

He is using A timing because he has N65 injectors.  While A timing and N65's do move the torque peak up to 1600 rpm from 1200 rpm with the standard bus tune, the torque curves I used to have before my old computer crashed show that the A-timed engine still makes a little more torque at 1200 than the standard engine.  Plus an MC-5B is not very heavy and responds well to the A timing with N65's even with a Spicer 4 speed.

I second the thought that if you don't have the buffer screw or switch installed, it won't idle well.  You definitely need the buffer to take the roll out of the idle.  You also need to have the idle speed set right.  Mine would not recover from dropping from high rev's down to idle well when the idle was set at 500 rpm.  I had to raise it to 600 rpm to get it kind of acceptable, and I will probably raise it another 25 rpm in the spring when I set out to play with it again.

Starting aid needs to be set right, and you need to set the running gap right.  The gap has a big effect on idle recovery, from what I have read.  Your engine, if it has the original governor, has an internal starting aid adjustment.  It won't have the throttle delay, though.

I don't have any ideas on the noise. 

Brian

[wg4t50]

Wibder why DDC would go to all the trouble of having standard AND Advance position cam timing since according to your  computer the Advance position gives more power even at the low end ?  Turely amazing and total different from our dyno tests that show drop in power under 1500 rpm with advance settings with additional heating