z20 cam timing

[Roger d]

I've got a z20 that was removed from a wreck in 1981. It only had 17,000 k on it. It was not stored right and had 150# in the front two cyls and 60# in the back two. So.....I rebuilt it. Thought I paid attention to how the cam was timed but apparently not. Got it back together and it ran ok, but not much better than before. checked the comp after a hard shakedown run, and it was 90# in the front three and 60 in the 4th. Checked timing again and it seemed out a tooth. reset. Now not as much power, and farting out the carbs. (twin Mikunis) Won't rev up smooth either. Ignition timing was @ 10o btdc. Compression seems to be 90# in all 4 now, but the intake valve on #4 not sealing. (bent?) Is there a simple way to check the cam timing? There are two shiny links on the chain, but they seem to wander all over the place. This motor is now in an '86 samurai. Shoulda kept the suzuki in it? Any ideas?? Thanks, Roger

 

 

[banzai510(hainz)]

the brite links are on intaial set up as once spun around it takes awhile for them to come back in the sma spot but most people just use the crank Zero mark and the cam sprocket timming marks up top. once you got that right then time the oil spindal/distributor correctly then youll have the basic motor timmed correcly.

 

I dont know how to adjust the vlaves on a Z head . Im sure somebody can chime in on this. a Z motor the cam lobes might be oppisite at TDC so ck carefully when on compression stroke to line everything up. Dial crank up to Zero then ck the oil pump spindal ,cam marks on head to see if cam sprocket is lined up or not

 

be nice if you have a Manual to help out also to match things up.

here is my Vid on L motors but lower end will apply.

 

this motor should be better torq wise than a Little Suzuki motor. As a friend had one and couldnt pull its way out of a Paper bag.

[datzenmike]

An '81 should be an 8 plug motor and that's too much timing. Try half that amount. Your compression is crap and the cam timing isn't causing this. Rebuild... what did you do for this 'rebuild' because going from 150 down to 90 is not right.

[Roger d]

Rebuild is new rings, deglaze, bearings and valve grind. Was also thinkin' not right!! Didn't move the crank, but not sure if the cam was lined up right. There are no cam marks on the head just the three spindle holes. Forgot to mark the chain and sprocket. Put it in #2 like it was but ????? Motor was like new inside, just been sitting a long time. Valve lash is mechanical, and is set to spec. (11-15 th) Pulled the head, and the valve just leaks, so I'll take it back to the machine shop. Noticed when I pulled it apart the head gasket must have been for a bigger engine as the bore is 2mm bigger.(saw it when it went together just didn't think it mattered?) Way more power and torque than the suzuki, but needs a 5spd. (10.50 x31 tires and 4.5" soa lift) Thanks for the replies, Roger

[Roger d]

Another thing, The ignition timing doesn't change at any rpm. Did this car have an ignition computer? 1981 510

[banzai510(hainz)]

a bigger bore head gasket isnot big deal.

My L16 is 83mm and I use a 85mm head gasket. Most Felpro and Nissan head gaskets are superceded to the bigger ones.

 

Make sure your adv spark wires are going to the right spot. either on the head or on the distributor cap.

But Im not a Z head guy. DatzenMike will know just wait for him to guide you thru this

[datzenmike]

To set the cam timing is the same as checking and adjusting for chain stretch. The Z head does not have the horizontal etch line on the cam thrust plate like the L series, in fact it doesn't even have a thrust plate.

 

Engine must be precisely at TDC #1 with cam lobes pointing downwards at about 8 and 4 o'clock. Be sure that the TDC is set while turning the motor in a clockwise direction only. If you over shoot back up well before TDC and try again. Do as many times as needed to get this right. This will keep the tension side tight and all slack on the tensioner side and give an more accurate reading.

 

Use a flashlight for the following...

 

Look just above the cam between the two rocker shaft towers for this tiny vertical casting mark. With the cam sprocket off it's easier to see...

 

 

Just like the L series, look through the cam sprocket hole to see if the V or U notch in the sprocket is directly below or just slightly to the right of the vertical casting line.

 

 

 

 

 

So.....I rebuilt it.... Ignition timing was @ 10o btdc. Compression seems to be 90# in all 4 now, but ....

 

Did you measure the cylinders to see if they were too worn for a simple hone and re-ring?

 

Squirt a couple of tablespoon fulls of motor oil into the plug hold and run the compression check again. If it goes up then the ring job is a bust. If not then it's the valve job that's a bust.

 

Borrow or rent a leak down tester and listen at the carb or exhaust pipe. If you hear hissing then the valve (either or both) is leaking. 90 PSI is terrible compression ... should be twice that.

 

 

Also need to know is this a Z20E or carb motor???

[Roger d]

Thanks for all the replies and info. It's a z20 carb model.

Here's where it gets interesting. I feel really stupid on this one! I removed the stock carb and it is now twin sidedraft mikuni carbed, and the back carb was "dead" and no response in the pilot circuit of that carb. Those cylinders were also low @ 60#. Startup procedure for twin mikunis is to first "sync the throttle plates". Didn't do that. Rear carb was shut tight @ idle so no air gets in. Compression test done with throttle wide open right? Wrong........Done a lot of work for probably nothing. Won't know 'till the new head gasket gets here and I get the #4 intake valve to seat. ( after I got the carbs synced, the compression was equal, just a bit low in #4, leakdown showed intake not seated. Still with throttle closed.....) GRRRRR...... Thanks for the info on the cam timing. From the pics it appears that the dowel is in line with that casting mark? I really don't want to take that front cover off! Any ideas on the ignition lack of advance? Should it have mechanical weights in the dist? It ran way better with 20o but I'm sure the cam was off. Many thanks, Roger

[Sealik]

Thanks for all the replies and info. It's a z20 carb model.

Here's where it gets interesting. I feel really stupid on this one! I removed the stock carb and it is now twin sidedraft mikuni carbed, and the back carb was "dead" and no response in the pilot circuit of that carb. Those cylinders were also low @ 60#. Startup procedure for twin mikunis is to first "sync the throttle plates". Didn't do that. Rear carb was shut tight @ idle so no air gets in. Compression test done with throttle wide open right? Wrong........Done a lot of work for probably nothing. Won't know 'till the new head gasket gets here and I get the #4 intake valve to seat. ( after I got the carbs synced, the compression was equal, just a bit low in #4, leakdown showed intake not seated. Still with throttle closed.....) GRRRRR...... Thanks for the info on the cam timing. From the pics it appears that the dowel is in line with that casting mark? I really don't want to take that front cover off! Any ideas on the ignition lack of advance? Should it have mechanical weights in the dist? It ran way better with 20o but I'm sure the cam was off. Many thanks, Roger

 

 

Not sure about the Mikunis when doing a compression test....but with the stock Hitachi or Weber there is only about a 5-8 percent increase with the throttle plates open....relative to closed that is.

Did you suck on the vacuum advance line to dizzy....any movement (breaker plate assembly)?...If so...does it stay in that position?

No leaks?

[datzenmike]

You did a leak down test? Did you hear air coming out the intake or exhaust? This will tell you if and where there is a leaky valve.

 

Just adjust the idle speed screws to open the carbs and re test. Like Doug says closed won't affect it much. 60 ad 90 PSI is deplorable compression. So rings or valves are bad.

 

Did you measure the cylinders to see if they were too worn for a simple hone and re-ring?

 

If the cylinders are worn past a rebuild then honing and re ringing won't contain the compression.

 

 

Squirt a couple of tablespoon fulls of motor oil into the plug hold and run the compression check again. If it goes up then the ring job is a bust. If not then it's the valve job that's a bust.

 

This is a good way to narrow down where the problem is.

 

 

 

Ignition timing should be about 5 degrees at idle. Disconnect and plug the vacuum advance hose and slowly rev engine... the timing should go up by about 25 degrees by 2,500-3,000.

[Roger d]

Air only coming out the #4 intake. Less air noise in crankcase than before re-ring. Valves re-ground. No wear on cylinder walls(17,000 klms since new) Can't do the oil thing 'till it's back together. Just pulled the dist apart and like the rest of the engine it's brand new inside. (super clean, and weights move freely) No U or V on the cam sprocket. Assume just put # 2 straight up? Thanks guys, Roger

[Sealik]

Yes.....No 2 on sprocket...dowel hole....'straight up'.

This will put the No 2 punch mark on the outer face of the sprocket at about 2:20 ish....pretty much the same here.

 

Disregard the bright link in pic....

 

 

This cam is advanced. Dowel is at No 3, straight up....punch mark is also now at 3.....(for the bright link, initial TDC/chain install)

Chain was marked...prior to wedging and sprocket removal

 

Oh.....PICS...would be a plus :D

[datzenmike]

The U or V notch is on the back of the cam sprocket.

 

 

 

 

Air only coming out the #4 intake. Less air noise in crankcase than before re-ring. Valves re-ground. No wear on cylinder walls(17,000 klms since new) Can't do the oil thing 'till it's back together. Just pulled the dist apart and like the rest of the engine it's brand new inside. (super clean, and weights move freely) No U or V on the cam sprocket. Assume just put # 2 straight up? Thanks guys, Roger

 

Can still be worn out. You said it was stored improperly.

[Roger d]

Sealik, Why advance to # 3 dowel? Datzen Mike, The "u" groove is there, just wasn't looking for the right "mark". (didn't notice it in the first photo) The storage comment was made before I tore it down the first time. I knew we hadn't oiled the cylinders or anything and had only turned it over once to see if it was seized. Just my thoughts trying to think of why the low comp on the back two. Assumed stuck rings. It was as new inside. Rings all free, everything very clean. Not even any oil "yellowing". All in all a very confusing project that really should be simple!!??

[Sealik]

 

 

 

 

I advanced the cam because I have a heavy truck/larger tires.....a little more bottom end....better on hills/out of the hole.

Whereas Mikes pic above is 'retarded'.....the cam that is :P ... :D ...at No 1 position, for top end.

 

EDIT

 

FWIW....there is not a significant/noticeable improvement when repositioning the sprocket.

I 'had' a new engine/TC assembly with the sprocket at No 2 position, hit a hill at about 2500 RPM in fourth and noted the how much the speed dropped....'dyno' for dummies so to speak. :D

Changed the sprocket to No 3.....hit the hill again... about 8 KPH improvement. Not much...but every little bit helps.

Although....a tale wind could of factored in on that 2nd test :lol:

[datzenmike]

Generally they are set on #2 position if the chain is not stretched. If the chain is worn and stretched the U (some are V) notch will shift to the left and the cam will retard and cam events will happen later in relation to where the piston is. Later closing intakes will slightly benefit very high RPMs while deteriorating manifold vacuum at low speeds causing lumpy idle and poor power. It doesn't matter what hole you use as long as the U notch to the vertical cam mark is preserved as described with the U just at or slightly to the right. THIS is the proper cam timing for overall good performance and economy from the factory. Each number is a 4 degree adjustment and that is what they are for. If the cam cannot be adjusted a new tighter chain will be needed.

[Roger d]

Finally got the parts in and valves re-done. I am putting it together and have a questio with regards to cam timing. I am setting it at the #3 dowel, but the "U" won't line up perfect with the casting mark. It is either to the left, or right but not centered. From the previous posts, I assume to the right is prefered?? Thanks for the help! :) Roger p.s. not sure how to add photos but could e-mail direct if needed.

[datzenmike]

Just under of slightly to the right is good.

[Roger d]

Seems to run good. Final report after we give it a good run over the break. Thanks for all the help and suggestions! Merry Christmas and a Happy New Year! :D Roger

 

EDIT: Put over 1500 klms on it over Christmas. Highway @3750 rpm for about 6 hrs, then 5 days of backcountry wheelin' in the snow and 6 hours return. Had some overheating issues due to Lucas oil additive that got in the antifreeze last time I took off the head.(what a mess, and a pain to clean out!) Did a compression test this morning and none of the cylinders were over 90#. Did it again with throttle wide open, and they all read 175#. I guess the intake runners on this manifold are just too short to get a proper read. Thanks again for all the help! You guys are the greatest!! :D Roger