Topic: input needed (cam-timing, measurments etc)

[Korven]

Hello guys, im trying to go through this engine i bought and that have never been started. i thought it would be a good idea to see whats inside and make sure all the clearances are there etc. There was some copperwashers on the sparkplugs so i figured there was a problem with them hitting the piston.

I did open it up and place some clay and do some cam timings.

Cam is a regrind of unknown spec but did these measurments.

total lift is 8.50-8.52mm on intake (0.335) on intake and a little less on exhaust 8.39.

All measurements at 0 valvelash and at 0.05inch or 1.27mm

In open 10.5 BTDC
    close 45    ATDC

intake Lobe center = 107.5
Duration at 0.05 is 235degrees and 244deg at 0.04 (wanted to compare it to my yoshimura camcard)

Ex open 46 BTDC
     close 4  ATDC

exhaust lobe center =  111degrees
Duration 230deg at 0.05

This gives a centerline of 109.25deg.


Think i went a little overboard with the clay but i wanted to measure the sparkplugs aswell.



I only did some quick measurments. There is less clearance on the inlet vale than on the exhaust. seems to be 1mm - 1.2mm. (How do you guys measure this for most accuracy? i do it with the digitalfeeler gauge bottom end). Defo a bit on the low side
Exhaust on the other hand seems to be 3-3.2mm.

I wonder if i should retard the cam a bit, i read that you could do this to add more inlet clearance. not sure if there are any big drawbacks to that. I would belive that the exhaust should have slightly more clearance because its hotter.



This is the measurements for the sparkplug. I added the sparkplug with the copper washer on cyl 1 and 2. (i did 3 n 4 without) but there seems to be some clearance there.






First off i installed the cam to oem spec.  (it was installed diffrently when i took it apart) on the picture below i installed it on the middle hole and it was installed on the white hole. i forgot to take measurements on how much diffrence there was between the holes, but i figure its atleast 10 deg?. I should probs get a slotted version, but is there any way that the other hole would give me any better measurements? seems to be way off.

[flatlander]

does the cam have any markings that might help identify it?

if not, then it might be an idea to adjust the cam so that the lobe centres are even. that's how most of them are designed to be run. you'd need a slotted cam sprocket to get that accurate.
and then check your clearances again. i expect they will be closer to each other than.

but let some real experts chime in as well. i've dialled in my cams with good results but there are others who have wider experience.

[bwaller]

Minimum valve clearance should be 1mm intake, 1.5 exhaust.

Is that a picture of a spacer you found under a sparkplug?

[754]

General I think clay is cut with a knife, the push half off to side , then use a tail on a verniervto measure , or you could use washers or shims . The last way , harder to read easier to make a mistake.
 I would try to use yourcsprocketbeven if you have to slot it a bit , before I would go to a slotted one, they should not move, but even better if they cant.

[teebee67]

I agree with bwaller  re clearances, we have always used 0.040" inlet and 0.060" exhaust. If the cam is a performance cam and you do not have full details I would re-install it to whatever it dialed in at before you took it out (taking it that, from the figures you describe, you measured the timing before pulling it down). If I remember correctly retarding the timing a little will increase top end power with a little decrease in mid range/bottom end. Advancing it has the opposite effect.

[MRieck]

 I measure valve to piston by gently prying down on the rocker arms at 10 degrees before and after TDC until it touches the piston. I use a dial indicator on the retainer. I hate using clay for valve to piston....thin solder is better IMO if you go in that direction. Clay is OK for checking the size of the valve relief.
 Your cam timing #'s are already retarded....I would advance the cam for better performance (about 105 LC). I would use a slotted sprocket too. Those fixed hole sprockets (like the old RC 750 sprockets ) do not offer real adjustability.

[Korven]

does the cam have any markings that might help identify it?

if not, then it might be an idea to adjust the cam so that the lobe centres are even. that's how most of them are designed to be run. you'd need a slotted cam sprocket to get that accurate.
and then check your clearances again. i expect they will be closer to each other than.

but let some real experts chime in as well. i've dialled in my cams with good results but there are others who have wider experience.

Only marking there is R5, so thats why i belive its a regrind. The rocker arms are standard.

I agree with bwaller  re clearances, we have always used 0.040" inlet and 0.060" exhaust. If the cam is a performance cam and you do not have full details I would re-install it to whatever it dialed in at before you took it out (taking it that, from the figures you describe, you measured the timing before pulling it down). If I remember correctly retarding the timing a little will increase top end power with a little decrease in mid range/bottom end. Advancing it has the opposite effect.

Acctually these measurements are with the cam in the standard position. middle of notch on cam aligned with the case. It was installed almost past the take out previously.

I measure valve to piston by gently prying down on the rocker arms at 10 degrees before and after TDC until it touches the piston. I use a dial indicator on the retainer. I hate using clay for valve to piston....thin solder is better IMO if you go in that direction. Clay is OK for checking the size of the valve relief.
 Your cam timing #'s are already retarded....I would advance the cam for better performance (about 105 LC). I would use a slotted sprocket too. Those fixed hole sprockets (like the old RC 750 sprockets ) do not offer real adjustability.

So basically in the area around TDC the pistons are at there closest to the valves? Why is clay a bad idea? wih thin solder is that just adding a 1+mm tin soldering wire to the piston?

You say i should advance my cam, will that give me less or more clearance. since im already a bit on the low side. perhaps more advance and thicker base gasket would be the best. The 500 seems to take a long time to adjust since you have to remove the rocker cover for each adjustment.

[turboguzzi]

agree with others here that clay is a bit unorthodox....and messy.
i mount light springs on the valves + dial gauge leaning on the valve retainer dish and just finger press until contact. best check a few points going from + 10 degress to - 10 around TDC to be sure. with this hand method you will see right away where is the point that it gets closest.

With the light springs you also dont need to lift the whole head every time to replace clay or solder as you try different timings win-win situation

look at megacylce's 500/550  cams specs, i use the 126-20, it will give you an idea on lobe centers, all my 2V fours are 105/105 to 108/108. wouldnt trust the position of the slot at the end of the cam too much on a regrind
https://www.megacyclecams.com/catalog/catalog.pdf

my 500/4 has 13:1 and no spark plug clearance issues... the pistons i see have also very low crown, a bit strange what the PO did with those spacers.

[scottly]

Those 3 large holes in the cam sprocket are not the holes for the 7mm bolts.

[MRieck]

Those 3 large holes in the cam sprocket are not the holes for the 7mm bolts.

One of the holes (the middle) is for a sprocket bolt.....somebody drilled the other 2 (and it wasn't done on a rotary table.) Somebody removed the rubber from the cam sprocket too....there are no lightening holes ( or any other except the center hole) on an OEM 550 cam sprocket.

[scottly]

I don't think so, Mike, but I may be wrong. I can see the threaded hole of the cam in the large hole on the right; it's obviously off-center and the hole is too big. The small hole at the right looks to be the proper size? I don't know about 550s, but I have a 750 sprocket with similar lightening holes. Can a 750 sprocket be used with a 550 cam?

[PeWe]

Can the washers under sparkplugs be a way to orient the plug with gap facing into the chamber?
I have read about that somewhere. Maybe a post on this forum or elsewhere.

[Korven]

If we look at the numbers i measure the cam at with lobes being about 2 degrees of the centerline, is that the amount of advance i should be looking for? 2 degrees that is.




Two pictures of how it was when i got it out. As many have discussed above i think the middle hole is slightly to large and must have been widned. im not sure if the smallest holes could have been where the plastic was attached?



This is how it looks with and without the washer on the sparkplug. Could there be any issue of the valve hitting the sparkplug since they are one overdimension? 28.5mm

[flatlander]

28.5 is one mm over stock which works fine. i have the same in my 550 and no problem with sparkplug interference.
the piston crowns also don't look like they would get too close to the spark plug.

regarding the cam, i'd get a slotted sprocket to have full flexibility in degreeing it. than set it so that the lobe centres have the same value both in and ex (example: 107in, 107ex). then measure again.

someone correct me if i'm wrong but from what i've observed, pretty much all cams for these sohc 2 valves per cylinder 500/550 hondas seem to be designed so that the lobe centres are equal.

[Korven]

http://www.webcamshafts.com/pages_misc/degreeing.html

Seems to be some info on here about cams

[Tintop]

Can the washers under sparkplugs be a way to orient the plug with gap facing into the chamber?
I have read about that somewhere. Maybe a post on this forum or elsewhere.

Called 'indexing' PeWe.  I've done this using multiple spark plug washers, & you can buy indexing washer kits with washers in various thickness. https://www.moroso.com/spark-plug-indexing-washers71910/  Theory is that orientating the gap towards the inlet valve promotes improved burn, & therefore more power.

[bwaller]

The smaller holes in the sprocket are indeed to lock the original damping material.  When I first dyno'd mine I spent some time specifically indexing sparkplugs. There was no noticeable difference and I tried 3 plug positions. That said I still orient the plugs to the same position because it's the right thing to do. An OEM inner valve spring shim is 0.5mm and I also have aftermarket 1mm shims. Either one of these will be all that's needed to index plugs. 

[PeWe]

Can the washers under sparkplugs be a way to orient the plug with gap facing into the chamber?
I have read about that somewhere. Maybe a post on this forum or elsewhere.

Called 'indexing' PeWe.  I've done this using multiple spark plug washers, & you can buy indexing washer kits with washers in various thickness. https://www.moroso.com/spark-plug-indexing-washers71910/  Theory is that orientating the gap towards the inlet valve promotes improved burn, & therefore more power.

Good info!
- Can plug color differ from one cylinder to another due to how the plug is oriented? Richer color if sitting "wrong"....

I'll mark plugs with a marker pen how the gap look like, then compare with another head to see how it should sit in the already sitting head. Tighten plug and see where it lands.

[PeWe]

Indexing my next to do.
I marked plug cyl 4 where gap face to.
Towards exhaust when tightened.
Thread pitch 1.25mm, same as a std M8.
I'll measure how long 1/2 turn will travel on an M8 with nut which will be thickness of shim.
Maybe more when it compress when tighten.

Interesting to see if plug color will change when facing to inlet valve.

[turboguzzi]

spark plug tip to valve clearance is a two second job to check.... just put the valve in the guide and see if touches the electrode of the plug, no clay required

Pewee, plug indexing might help in a design where the plug is badly masked... if the dyno will see any difference in an good open chamber like the 750s, it will be half  a miracle... IMHO of course...

[MRieck]

 As an aside you have good valves and springs in there.....all Kibblewhite.

[Tracksnblades1]

Can the washers under sparkplugs be a way to orient the plug with gap facing into the chamber?
I have read about that somewhere. Maybe a post on this forum or elsewhere.

Called 'indexing' PeWe.  I've done this using multiple spark plug washers, & you can buy indexing washer kits with washers in various thickness. https://www.moroso.com/spark-plug-indexing-washers71910/  Theory is that orientating the gap towards the inlet valve promotes improved burn, & therefore more power.

Has the indexing theory changed. A while back it was encouraged to index the spark plugs' open gap towards the exhaust  valves. Then the theory was the compressed mixture closest to the hot exhaust valve was more likely to ignite at the preset ignition lead BTDC. Further believing then that the hottest part of the mixture would be more likely prone to detonation (limiting optimal ignition lead) due to the heat radiating from the approaching flame front.

[Tintop]

My experience is/was with TC's with center plug position between the valves (hemi-ish).  In that situation I was taught you want the gap facing the inlet to create an equal flame front around the plug towards the exhaust.  I can see in a head like the 750 with the plug off-set, that having the gap facing towards the center between the valves would be better.  Mercedes Benz calls for the gap to be indexed within a 45* spread either side in the injector, which is centered between the valves.  I've no experience with forced induction, or exotic fuels so their requirements could be completly different. 

[Tracksnblades1]

My experience is/was with TC's with center plug position between the valves (hemi-ish).  In that situation I was taught you want the gap facing the inlet to create an equal flame front around the plug towards the exhaust.  I can see in a head like the 750 with the plug off-set, that having the gap facing towards the center between the valves would be better.  Mercedes Benz calls for the gap to be indexed within a 45* spread either side in the injector, which is centered between the valves.  I've no experience with forced induction, or exotic fuels so their requirements could be completly different.

Yes, I will concur, cylinderhead design would ultimately determine the best sparkplugs location...and then it would take a good dyno to prove it....

Being a unworthy disciple of the late great Smokey Yunick, I would hope more than convenience went in to designing the Chevrolet Performance Cylinder Heads. Like Ford, HP Chevrolet wedge (quench) ( including SBC angle plugs) chambers  are all machined with the sparkplugs near the exhaust valves.

As far as exotic fuels and superchargers are concerned, with A/F ratios near or at 1:1, My concern would be if the mixture didn't vaporize prior to igntion.... Would there be enough room to prevent a hydrolock....?  Sharing Mr Yunick's publishing, "At 11:1 c/r you can survive a misfire, but if your not squeezing it over 14.5:1 someone else will and you'll lose"...

.  tractor diesel pulling injectors are 1450cc ( winners are mum) compression is down below diesel self ignition levels (hydrolock?) compound Turbo boost levels are north of 200psig...its usually bad if the turbos don't light(spool) and stay lit for the entire run...

As far as sparkplug indexing with oxygenated fuels, the ground electrodes faced the intake valve, acting as a shield for the gap, because it's going to get real wet.  For real high compression chambers the ground electrode was positioned where it didn't contact the piston dome...

There are some guys on here still playing the game, their knowledge would be current....I know one guy here that has a big motor about as far as he can on gasoline....without putting a belt driven air cleaner or some suba tanks on it...😃

[PeWe]

Searched for sparkplug shims.
How have I missed that?

They are sold everywhere. Recommendation that plug gap facing inlet. I'll try the land between valves too. All 4 with same orientation.
Lets see if I can find 12mm plug shims nearby.

I do not expect more power, only equally set plugs so the orientation does not affect plug color which is receipt on the burn.