Piston & valve clearance issues

[JamesG]

The tapping could be insufficent squish band clearance. When you had the motor apart did you notice any shiny wear marks on the perifery of the piston or head?

This month's RRW magazine has a very good article on race engine building. When I read it I thought of your ordeal Darrell.

[dgyver]

ARGH...SQUISH!!!!....do not talk about squish!!!!  :x  I have read too much about squish during my endeavor with 2-strokes.

I did not notice any shiney wear marks but then was not looking either. I did look for impact areas which I guess would look the same. Since these are used pistons, there may be some play with the pistons and the cylinder walls. I will pick up the RRW mag to see if it will help me figure out what I am doing wrong.

I tried another set of plugs to see if the other ones were fouled and no change. It was easier to start and would idle but at a very low rpm, >1K. I agree that I may be too rich at idle but I do not think that I would be too lean when I crack the throttle. But then I suck at jetting. Sometimes I should just ignore my logic. I may try swapping a few jets to see if anything changes. But the tapping/knocking sound still exists.

A buddy called me tonight, who used to built Fiat X19 motors, and he described the tapping sound as a diesel knock and had the problem of the wrist pins being loose in the rods. Did not check the pin-piston fit but they are the same pins I was using with the 75mm pistons without any problems so the pin-rod fit should be fine. From what I remember the pins were a tight fit in the pistons. I do have 2 sets of pins and may have switched them I do not remember...damn CRS (too many head injuries).

Oh well, since I am going to have to pull the cylinder to check the pins, I am going to put the 75mm pistons & cylinder back in with the head & cams that are installed now. Hopefully that combination will work. I am supposed to have another bottom end on the way, so I will build a second motor off the bike.

I need to have a running motor soon so I can make the Jennings track day on May 9th and this is probably the only weekend I have left to work on it.

[dgyver]

This month's RRW magazine has a very good article on race engine building. When I read it I thought of your ordeal Darrell.

I picked up the April issue of RRW but did not see an article about engine building. Was it in the Feb or May issue?

[Rema1000]

I have a air/fuel ratio meter. I installed an oxygen sensor in the exhaust.

Is that a junkyard O2 sensor off a car?  That would speed the jetting process nicely.

[dgyver]

The knocking sound has been eliminated. The pistons where hitting the head. With such a high dome, the pistons were tapping the rim of the head cavity. A little grinding on the head and all is good. Grinded some off the pistons as well to allow for plug clearance. The copper washer were not sealing all that well.

I have not changed the jets yet so it only idles. Adjusting the air screws helped in starting. It still dies when I open the throttle. I will increase the mains and hope it helps.

[JamesG]

Its the may issue, Part of the AOD/NOTB articles; "How to go racing".

Its not super in depth, more suggestions and tips on race prep and engine assembly.

[dgyver]

Its the may issue, Part of the AOD/NOTB articles; "How to go racing".

Its not super in depth, more suggestions and tips on race prep and engine assembly.

They did not have the May issue yet...maybe this week.


An update on the motor upgrade (or degrade in this case)......

I am getting confused and really frustrated....I put the 500 cylinder back in with the milled & ported head, megacycle cams & jetted with 147.5/40/3turns (the same jetting as before with the 500 and stock head & megacycle cams). The bike will "run" with a low rough idle, like the timing is off. Open the throttle and no real change in rpm's. The carb slides do not lift with the twisting of the throttle. I checked the compression and vacuum (by cover the carb & plug holes with my hand & finger) and there seems to be plenty of both. The valves seat fine. Good spark. What am I missing?

:x  :x  :x  :x  :x

Dang this is frustrating....thinking about swapping heads and put the stock head with the megacycle cams since I had it running with this setup before. I never had the bike running with the milled head.

Any other suggestions or advise that I may be overlooking?

:dunno:

[Blueknyt]

You using an Advancer on it? sure your Cams are set right ?(pref using degree wheel and dial indicator)  there should always be a change when you open throttle, slides moving or not. you useing stock Carbs?

[dgyver]

The carbs are stock and has a V&H ignition advancer. I keep double checking the cams and they are correct.

[JamesG]

Are you installing the cams/setting timing with the V&H rotor on?  I never trusted the timing marks on those rotors so always put a stock one to do the cams.

The only thing I can think of would be off timing, unless you had a massive cylinder leakage somehow (you did remember to put a head gasket on right    )?

[dgyver]

I am setting the timing with the V&H advancer. I can swap rotors to verify the settings. It does feel like the timing is off but I can not figure out where/how. Yes, I do have a head gasket.

[JamesG]

Are these the megacycle cams you are using?  Have they had the sprockets slotted and moved?

[dgyver]

They are megacycle cams and the sprockets have been slotted and moved. One thing I did do before taking anything apart, is marking the cams and rotor, when the cams are not pushing down on the valves, with a mark to help with reinstalling everything. I then check the timing according to the service manual.

[JamesG]

Darn, I was hoping to get the cookie! :lol:

I donno man, Before I mangled mine...  I had a lot of trouble getting the timing right with the MC cams. It was like they would always be one tooth/chain link back or forward and it would run like crap.  I spent many hours at TGPR one weekend rearranging the cams before I finally got them right.

What I finally discovered thru serindipity (laziness) was that by leaving the chain tensioner in and letting it put tension on the chain, it keeps the sprockets more lined up and prevents them from slipping as you tighten down the holders.

[dgyver]

Adjusting the cams? Are you referring to just moving the chain a tooth front or back on the cams? Were you adjusting the degree of the sprocket on the cams?

I know the factory alingment marks on the cams are not 100% accurate since they have been degreed.

[dgyver]

I have been rereading my diary here. This is what I have come up with...

500 cylinder with stock head & MC cams - ran fine, pre-rebuild condition
555 cylinder with stock head & MC cams - ran with throttle response but w/ clearance issues
555 cylinder with milled head & MC cams - runs with rough idle & no throttle response
500 cylinder with milled head & MC cams - runs with rough idle & no throttle response

I do not understand how, what or why but the only common item related to the problmes is the milled head. I will be swaping heads later in the week.

BTW...what thickness copper gasket should I get? I am going to order one for the 555 for when I try installing it, again.

[V8Pinto]

Consider the fact that you may be moving a lot more air because of the increased displacement.  More airflow through the same size passages means a (more velocity) stronger vaccuum signal at the venturi which will pull more fuel through the same size jet.

So a smaller jet size may actually be needed.

This is sort of common in car motors where an inefficient motor will need more "jet" to cover up a velocity problem than a better put together motor will.  (usually a person is over-camming).

I am unsure of this term but is this related to BSFC?  (Brake Specific Fuel Consumption).  

Maybe some SAE guys can chime in?

Shane
306 N2O Pinto

ps. I mentioned over-camming but I truly don't believe in such a thing.  I believe in my heart that there is no such thing as too much cam, just not enough motor.