78 620, L20B foreign matter in combustion chamber.

[datzenmike]

On an L20B the intake closes at 52 degrees after BDC and relies on the inertia of the intake air to keep moving into the cylinder even with the piston rising against it.

 

If the cam is timed so the events happen slightly later than they should. In other words like a stretched chain or lower numbers on the cam dowel or the chain moved a link clockwise. Then the intake closes with the piston farther up the cylinder. At low speeds this would push some of the intake air out of the cylinder just before the valve closes. Less filled cylinder is less likely to ping and easier on the starter. At ultra high RPMs the reverse is true and the fast moving intake air is still rushing in on the late closing valve, cramming more air in than an earlier closing.   

[distributorguy]

Can you figure out the intake valve centerline?  It sounds to me like the cam is 1 tooth off, so the timing has to be adjusted roughly 13 degrees to make it work right.  Look for between 103-110 degree intake centerline ATDC.  If you're less than 100 or over 120, its off.  

[wayno]

Can you figure out the intake valve centerline?  It sounds to me like the cam is 1 tooth off, so the timing has to be adjusted roughly 13 degrees to make it work right.  Look for between 103-110 degree intake centerline ATDC.  If you're less than 100 or over 120, its off.  

 

I don't even know what any of this means except for the statement, "It sounds to me like the cam is 1 tooth off", this is why you can build race engines and I just dream about building engines with more power.

I tried to get a photo of the groove/notch on my engine, but the camera would not focus that close, my notch is at least a 1/16th left of center of the groove on the retaining plate while Dmike's photo is a 1/16th right of center of the groove, it is not that far off now compared to how much it was off, I just have to see if it knocks/pings much now, it didn't knock/ping much before changing it, but I was at maybe 4/6 degrees advanced on the ignition timing, right now I am at 2 degrees, keep in mind everyone that I burn regular pump gas, I have a reason for burning that grade which I will not get into here.

[datzenmike]

Well wayno you can try it where it is now in the new location and see if better or worse and you can try moving one dowel higher which will advance the cam 4 degrees and try it. I guess in the end it's where YOU like it. After all this isn't a stock engine any more, there's no reason to believe the ignition or cam timing will be.

[Stoffregen Motorsports]

Wayno, if you have a dial indicator on a wobbly base (commonly used to measure brake rotor runout) - https://jet.com/product/detail/820f2a0010b84ea7a5fcb62ed8a5cd81?jcmp=pla:ggl:b_nj_dur_gen_tools_home_improvement_a2:tools_home_improvement_plumbing_water_heater_parts_accessories_a2:na:PLA_858550035_47529561030_pla-313882465144_c:na:na:na:2PLA15&code=PLA15&pid=kenshoo_int&c=858550035&is_retargeting=true&clickid=73cb6fc2-ed17-41a8-ae16-a459668b9585&gclid=EAIaIQobChMIw9OXxfun1wIViZ9-Ch1ctAqqEAQYByABEgJWEPD_BwE, you can learn the easier "split overlap" method of checking your cam timing. It is very easy to learn and it offers you more usable info as to what your cam is doing than the degree wheel.

 

This thread explains the method, but I do it a bit differently.

http://www.calverst.com/technical-info/cam-timing-mechanical-method/

 

If you are interested, I can walk you through the process.

[wayno]

I am just going to drive it and see what it does and go from there, if it is knocking/pinging at 2 degrees I will likely have to put it back the way it was, the last drive I could barely hear any knocking/pinging as the SU carbs are making way more noise, but I could clearly hear over the SU carbs before when it was knocking/pinging like crazy at 8 degrees before TDC, I have to get used to the carb noise and then I will be able to hear it knocking/pinging even just a little bit.

I only had issues with knocking/pinging when it was hot outside in the past, and it barely knocked/pinged, I could get it to stop if I floored it or let off, it knocked/pinged every few seconds in the sweet spot when going up slight grades, it didn't happen enough to re-time it although I did re-time it to get to that point, now I am starting over as it is different with the cam timed the way it is now, the SU carb noise is way louder.

I used to use a modified 510 air filter housing, I had that for years, but when I installed a power brake booster I had to loose that giant housing and I then switched over to thin pancake filters, that made a little more noise, but now I can hardly hear myself think let alone hear the radio, I might have to make a custom air filter setup, like a square tube going from the carbs to an air filter housing like the diesel canister with a rubber boot/tube between them, maybe I can put material on the tube to make it quieter, I might be able to tilt the engine towards the passenger side just a little more to make a little more room between the carbs and the booster.

[distributorguy]

Here's the easiest way to degree a cam properly:

http://www.cranecams.com/uploads/instructions/803_.pdf

 

Essentially you check for peak lift of the #1 intake cam lobe, measured at the spring cap.  You can figure out degrees on your balancer without having to buy a degree heel by simply measuring the circumference to the nearest 1/64".  It should happen around 110 degree ATDC, +/- 5 degrees.  This is measured with a dial indicator with a magnetic base - about $30 at Harbor Freight.  Essentially, get toward 112 you get more torque.  Get toward 105 you get more hp.  

[Stoffregen Motorsports]

Wayno, one way to get more room at the booster is to relocate the booster itself. Move the clutch pedal over as needed to be able to run the booster right up against the firewall. It's not as much work as it sounds.

 

Jeff, have you ever used the split overlap method? It is so much simpler than using a degree wheel. All you need is TDC and a dial indicator. The results of this method quickly let you know if the cam is advanced or retarded.

[wayno]

Wayno, one way to get more room at the booster is to relocate the booster itself. Move the clutch pedal over as needed to be able to run the booster right up against the firewall. It's not as much work as it sounds.

 

 

 

I thought about that but figured out how to make it work, it still doesn't move the booster over any, it just doesn't work with SUs, it does work against the firewall with everything else, I had power brakes on the 520 with the booster in the stock position(masters are farther part), but when I put SUs on the 520 I had to install a 521 pedal assembly in the 520, when I figured that out I thought I can do this to my 521 work truck, so I did it to the work truck also and that is it in the photo above I posted.

I am starting to get confused on my ignition timing, I guess it was at 6 degrees before TDC and it knocked/pinged like crazy, so I re-timed it to 3-4 degrees before TDC and it still knocked/pinged when going up hills, but now when I floor it it doesn't go away like it did before, so after I got home I re-timed it again at 2 degrees before TDC and I am hoping it stops knocking/pinging on the upgrades as I have a lot of weight to get up them hills and I cannot be babying it, it has to go up the freaking hill.

I did notice something else today, I am not using as much of the pedal now to go the same speeds, I am actually near the top of the pedal  most the time, but it was dry out and no wind to speak of, maybe I will get better mileage out of this, that is a positive thing, while knocking/pinging is a negative thing.

While I am only using the top of the pedal the noise isn't too bad, but when I start putting my foot in it it  get very noisy, at lower rpms it has a pulsing sound, but after 2000rpms it becomes a steady howl, I never had my engines sound like this before, I expect all my engines are timed wrong(cam timing) as I did all of them the same way, TDC, 10am/2pm, and the distributor around 3:30pm to 4pm, all of them are like the work truck engine was since 1995 when I put my first super head on my L20b, 22 years of being set up wrong, and of course me telling people all these Ratsun years how to set it up wrong, but they all ran great that way.

[Atikin9000]

Kind of off topic, any suggestions on cleaning deck of gasket material, leaning towards the permatex gasket remove and some elbow grease but I was also looking at the roloc discs. Any opinions?

[datzenmike]

Scraper and then something like scotchbright. You want to polish. Be even more careful on the softer aluminum head.

[Atikin9000]

Scraper and then something like scotchbright. You want to polish. Be even more careful on the softer aluminum head.

Head is good to go. Just need the block cleaned and Id rather avoid scrapers and razer blades, I got big manly hands and don’t trust myself to finess.

[Atikin9000]

They have the bristle discs in 60-80-120 grit. Idk if I’m

Gonna need all 3.

[datzenmike]

No you only need to get the old gasket off. More aggressive wheel just does it faster.

[wayno]

I use a brass wire wheel on my air cutting tool, it takes a while but when done it is clean and no metal was removed.

I would never use a flap disc on a engine deck or head, I don't know what a bristle disc is.

[Atikin9000]

I use a brass wire wheel on my air cutting tool, it takes a while but when done it is clean and no metal was removed.

I would never use a flap disc on a engine deck or head, I don't know what a bristle disc is.

http://multimedia.3m.com/mws/media/58801P/3mtm-roloctm-bristle-disc-yellow-2-inch.jpg

 

these little guys from 3m

[wayno]

Never seen one of them before, would have to try one to know what I would use it for.

 

BTW, I got off topic here, I think it was the photo of the cam timing that made me react, it trashed everything I ever believed about how to time my cam, and I kinda took over this thread for a while.

[Stoffregen Motorsports]

Kind of off topic, any suggestions on cleaning deck of gasket material, leaning towards the permatex gasket remove and some elbow grease but I was also looking at the roloc discs. Any opinions?

Noooooooooooooo!

 

Roloc discs have screwed up more cylinder heads than anything else you can use.

 

Elbow grease, a razor blade, some 220 grit emery cloth on a 2x2 piece of wood, lubricated with WD40. That's how you get it clean and ready for use.

[Stoffregen Motorsports]

I thought about that but figured out how to make it work, it still doesn't move the booster over any, it just doesn't work with SUs, it does work against the firewall with everything else, I had power brakes on the 520 with the booster in the stock position(masters are farther part), but when I put SUs on the 520 I had to install a 521 pedal assembly in the 520, when I figured that out I thought I can do this to my 521 work truck, so I did it to the work truck also and that is it in the photo above I posted.

I am starting to get confused on my ignition timing, I guess it was at 6 degrees before TDC and it knocked/pinged like crazy, so I re-timed it to 3-4 degrees before TDC and it still knocked/pinged when going up hills, but now when I floor it it doesn't go away like it did before, so after I got home I re-timed it again at 2 degrees before TDC and I am hoping it stops knocking/pinging on the upgrades as I have a lot of weight to get up them hills and I cannot be babying it, it has to go up the freaking hill.

I did notice something else today, I am not using as much of the pedal now to go the same speeds, I am actually near the top of the pedal  most the time, but it was dry out and no wind to speak of, maybe I will get better mileage out of this, that is a positive thing, while knocking/pinging is a negative thing.

While I am only using the top of the pedal the noise isn't too bad, but when I start putting my foot in it it  get very noisy, at lower rpms it has a pulsing sound, but after 2000rpms it becomes a steady howl, I never had my engines sound like this before, I expect all my engines are timed wrong(cam timing) as I did all of them the same way, TDC, 10am/2pm, and the distributor around 3:30pm to 4pm, all of them are like the work truck engine was since 1995 when I put my first super head on my L20b, 22 years of being set up wrong, and of course me telling people all these Ratsun years how to set it up wrong, but they all ran great that way.

I think you have some home work to do. Have you ever checked your total timing? Have you ever verified TDC? You should be able to set the initial timing at around 12 degrees, so if you're pinging at 2 degrees, either your distributor has way too much advance, or the timing pointer may be off. But if your cam timing is off, then all bets are off.

 

Surging could come from poor fuel delivery or bad ignition parts too. You say partial throttle gives a better feel of acceleration? Check your fuel flow, float level, coil, cap, rotor, plug wires. Do you know how to check that the well jet needles are properly adjusted?

[Atikin9000]

Noooooooooooooo!

 

Roloc discs have screwed up more cylinder heads than anything else you can use.

 

Elbow grease, a razor blade, some 220 grit emery cloth on a 2x2 piece of wood, lubricated with WD40. That's how you get it clean and ready for use.

 

I’m cleaning the block, not the head.

[Crashtd420]

It can mess up both.... just not a good idea on either surface....

[Atikin9000]

It can mess up both.... just not a good idea on either surface....

So razor blade is the safer solution? Lol

[Crashtd420]

In a sense..... the biggest thing is you don't wanna create low spots that grinding disks and such can do.....

Keep it wet with something like wd40 and the blade at an angle..... better to take your time then trying to be quick about it

[Atikin9000]

It’s a rubber bristle disc, are you sure we’re talking about the same thing?

[Crashtd420]

It’s a rubber bristle disc, are you sure we’re talking about the same thing?

Maybe maybe not.... either way you just need to becareful you dont make low spots.... if what your talking about cant and wont remove metal then technically it would be ok.... no matter how you get it done your biggest concern is flatness..