Poor cylinder running and cam timing

[Commando77]

From my thread in what's annoyed I'm still seeng poor running after a case split (gearbox and crank brgs) etc. Despite lots of carb cleaning, checking seating etc she still refuses to pull well on rear pot. So I decided to revisit timing and have a question. While, like many it seems mine won't align the gear dashes exactly when the RT and FT marks are on the case joint/alt cover notch etc. Even did a full scale drawing which when cam gear dashes are all parallel with head surface has the FT mark at 9 deg Btdc and the RT at 5 deg Atdc. Moving the wheels a tooth either way seemed to make too big a difference but my latest measurements suggest I could get each cylinder within 3 degrees.(appx measure on periphery of rotor). However my question is how big a cam timing difference would affect compression test as I'm now getting 160 front and 130 rear. Engine has been run 10-15 mins now.
Rear downpipe runs hot as front and it doesn't misfire, just seems weak or out of phase with front. A hand over the front carb stops it straight away, doing the same with the rear has some effect but it seems to be doing so little and it carries on running. How I got 150 psi in both before Xmas I have nfi! But i have messed with cam timing. Tested it three times today and consistently 160/130. I guess the head has to come off but the timing still bugs me. Am I wasting my time here? Cheers for any responses. I didn't expect to rock up the rebuild like this

[Chris58]

From my thread in what's annoyed I'm still seeng poor running after a case split (gearbox and crank brgs) etc. Despite lots of carb cleaning, checking seating etc she still refuses to pull well on rear pot. So I decided to revisit timing and have a question. While, like many it seems mine won't align the gear dashes exactly when the RT and FT marks are on the case joint/alt cover notch etc. Even did a full scale drawing which when cam gear dashes are all parallel with head surface has the FT mark at 9 deg Btdc and the RT at 5 deg Atdc. Moving the wheels a tooth either way seemed to make too big a difference but my latest measurements suggest I could get each cylinder within 3 degrees.(appx measure on periphery of rotor). However my question is how big a cam timing difference would affect compression test as I'm now getting 160 front and 130 rear. Engine has been run 10-15 mins now.
Rear downpipe runs hot as front and it doesn't misfire, just seems weak or out of phase with front. A hand over the front carb stops it straight away, doing the same with the rear has some effect but it seems to be doing so little and it carries on running. How I got 150 psi in both before Xmas I have nfi! But i have messed with cam timing. Tested it three times today and consistently 160/130. I guess the head has to come off but the timing still bugs me. Am I wasting my time here? Cheers for any responses. I didn't expect to rock up the rebuild like this

My cams also would not line up perfectly to the case either.. maybe a few degrees out. I suspect a slightly streched out cam chain.. I just put it as close as possible and it makes great power, so that is not likely the problem with yours.
If its bothering you, just slot the cam sprokets out a bit and get it timed right.

Have you tried doing a pressurized leak down test on each cylinder?
While doing the test listen for gases escaping in the intake, exhaust, and oil fill cap to determine where you are losing compression.

I am not sure if you had the heads apart, but if you removed the valves and they didn't go back in the exact same spots, the may have a valve sealing issue.

[Commando77]

Thanks. The head had not been apart but it has now! Nothing wrong with it, the valves or the gasket. Filled the ports with fuel and nothing leaked after an hr. Pulled all the valves and they are good, no nicks nothing. Lightly ground the exhausts.
Back to timing, I think I've just got it wrong. With all cam wheels parallel and aligned with head the front FT mark is 10mm above the window notch. The rear RT mark is 6mm below the window notch. That's about 12.5 deg difference. For now I'll put it down to my bad close vision and relook tomorrow.
Still wondering why such a difference in compression readings unless I have a bust ring. Pistons never came out so I can't have damaged them. Does cam timing have a big effect on cylinder fill and compression?

[Varastorm]

It's always hard to find a fault if you never did the work yourself. Like rebuilding an engine someone else has half done & given up on 6 months ago

I've had a quick read & tbh I'm reaching here, but could it be timed 180° out?

Also, is it a quality (Snap-on ) compression tester or a (Blackspur ) item?

[Chris58]

Thanks. The head had not been apart but it has now! Nothing wrong with it, the valves or the gasket. Filled the ports with fuel and nothing leaked after an hr. Pulled all the valves and they are good, no nicks nothing. Lightly ground the exhausts.
Back to timing, I think I've just got it wrong. With all cam wheels parallel and aligned with head the front FT mark is 10mm above the window notch. The rear RT mark is 6mm below the window notch. That's about 12.5 deg difference. For now I'll put it down to my bad close vision and relook tomorrow.
Still wondering why such a difference in compression readings unless I have a bust ring. Pistons never came out so I can't have damaged them. Does cam timing have a big effect on cylinder fill and compression?

yeah sounds like maybe you have the cams off one tooth.. or as varastorm said, it may be 180 deg out.

I would re do the timing procedure exactly how the manual states. Read carefully and its easy.

[Commando77]

Thanks for ideas. We'll I'm the one that took it apart to fix a noisy gearbox brg. While in there I decided to do the shells and that involved disturbing the chains which I didn't think would be an issue with all the information out there! I have a honda manual too. Cams are pointing in on the offending rear cyl as per book.... 180 out would have them pointing out like the front... No?
The tester is an old gunson, maybe not the most accurate but it matches an old hawk I also have. The last test was done three times and all were within a psi or two. The last tests were done after moving the cams a week ago. One went up 10 psi and one down 10psi. I'll keep persevering... Cheers.

[MacV2]

Thanks for ideas. We'll I'm the one that took it apart to fix a noisy gearbox brg. While in there I decided to do the shells and that involved disturbing the chains which I didn't think would be an issue with all the information out there! I have a honda manual too. Cams are pointing in on the offending rear cyl as per book.... 180 out would have them pointing out like the front... No?
The tester is an old gunson, maybe not the most accurate but it matches an old hawk I also have. The last test was done three times and all were within a psi or two. The last tests were done after moving the cams a week ago. One went up 10 psi and one down 10psi. I'll keep persevering... Cheers.

OK as I understand it the 180* out relates to the two cylinders...obviously...Its no good just saying the rears are pointing the correct way its the relationship between the front & rear...So if the rears are correct at TDC what are the fronts doing ?

So follow the guide & set the rear to TDC then turn the crank to front TDC & remember the front marker needs to come round in effect twice...

''450 degrees (one and quarter turns) until the FT lines up with the alignment marks through the inspection window. You will find the FT comes around once and then on the second time you see it you would have turned it 450 degrees and be on the compression stroke. You will also find the FT comes around directly after an F mark, be careful to stop on the right one. If you miss the mark, then go around once again remembering that the FT comes into view once and it's the second time that it comes into view that you stop, so your essentially going around twice and always turn in an anti-clockwise direction.''

As I understand it if you stop on the first FT mark that then is when is 180* out...It'll still run but when you get up to 4 or 5k revs it just runs out of puff...

This of course dosent explain the low compression on the rear...or does it ???

[Varastorm]

Thanks for ideas. We'll I'm the one that took it apart to fix a noisy gearbox brg. While in there I decided to do the shells and that involved disturbing the chains which I didn't think would be an issue with all the information out there! I have a honda manual too. Cams are pointing in on the offending rear cyl as per book.... 180 out would have them pointing out like the front... No?
The tester is an old gunson, maybe not the most accurate but it matches an old hawk I also have. The last test was done three times and all were within a psi or two. The last tests were done after moving the cams a week ago. One went up 10 psi and one down 10psi. I'll keep persevering... Cheers.

OK as I understand it the 180* out relates to the two cylinders...obviously...Its no good just saying the rears are pointing the correct way its the relationship between the front & rear...So if the rears are correct at TDC what are the fronts doing ?

So follow the guide & set the rear to TDC then turn the crank to front TDC & remember the front marker needs to come round in effect twice...

''450 degrees (one and quarter turns) until the FT lines up with the alignment marks through the inspection window. You will find the FT comes around once and then on the second time you see it you would have turned it 450 degrees and be on the compression stroke. You will also find the FT comes around directly after an F mark, be careful to stop on the right one. If you miss the mark, then go around once again remembering that the FT comes into view once and it's the second time that it comes into view that you stop, so your essentially going around twice and always turn in an anti-clockwise direction.''

As I understand it if you stop on the first FT mark that then is when is 180* out...It'll still run but when you get up to 4 or 5k revs it just runs out of puff...

This of course dosent explain the low compression on the rear...or does it ???

Excellent write up Mac

[Commando77]

Thanks for all that.... I did do the mccts last Yr so I'm familiar with the procedure.... You'd think!! . Its definitely on the right tdc and cams pointing in as is the front cams pointing out which runs fine anyway. I'll aim for the same as the front and we'll see. They are definitely different. Cheers again. Waiting on head gasket now. On a different tack I saw only one head dowel.... You guessed it, the other was sitting in the oil pump drive area. She's testing me all the way!

[Varastorm]

On a different tack I saw only one head dowel.... You guessed it, the other was sitting in the oil pump drive area. She's testing me all the way!

Like I mentioned above, about your own V's someone else's work. If someone had questioned you about the location dowels.. I bet you'd of sworn they were tip top.

The big question is what else has she done under your supervision

[tony.mon]

About the position of the crank marks when the cams line up, the crank rotates twice as often as the cams, so your 12.5 degrees off is half that of the camshaft.

As suggested, unless you slot the sprockets you'll rarely get the marks aligned exactly but it makes little difference to power and none to compression.

Just set it to the nearest tooth.

[Commando77]

Varastorm, thanks for that vote of confidence but you're right, it makes you wonder what other feckups are lurking. By nature I'm dead careful the first time I strip something mechanical and I've tried to apply that to this strip down. I've still messed up it seems.
Tony Mon, I'm going with that any have just got back on the job. Head gasket arrived so all together and cams all aligned with the head, RT and FT text in middle of hole. No way would a tooth get it closer so its got to be right. They seem to be very close anyway. Cams are pointing in correct directions.
Carbs cleaned again and carefully rodded with coated wire (no drills). Replaced rear ht lead and plugs. Coils both measure 1.2 ohms, is that good as I can't find LT specs?
Only one other thing I've not checked is the crank trigger. I know it only fits one way but if say it wasn't seated when torqued could it be positioned so its OK on one cylinder but retarded on other? That's too weird I know, or do both plugs fire together (wasted spark)?
Thanks, should get it fired Friday.

[Varastorm]

Yes, you're correct in thinking it has a wasted spark & can allow it to fire 180 out

[tony.mon]

If you time one cylinder 180 out it sounds strong and sharp and runs beautifully up to around 5k revs, then won't pull much over that.
Doesn't sound like your problem at all.

Re the crank trigger, there's almost no movement available to it as the holes are tight clearance to the mounting bolts, so it's either mounted or not, there's no adjustment possible.

Did you shim the head on the bench before fitting?
I find that you need to recheck and sometimes re shim after it's been torqued down
But it won't vary enough to stop the valves seating and losing compression like that.

For peace of mind, lift the cam buckets and re check that the valve collets are still in place securely.
And it might be worth checking that the valve stem isn't binding in the guide, but again, unlikely if you left the old guides in the head.
I once found that a guide had cracked following a cct failure and bent valve scenario.

[Commando77]

No it doesn't seem so. I shimmed the valves when the motor was out and it only took tiny changes. I went for looser than tighter than spec, some are bang on others a thou (.025) over. With the head off they were about the same, ..012 larger but when I shimmed them it was a warm 20 deg workshop and when the head was off it was only 5deg ish. The buckets all return freely, none seem to hang up. Collets seated with a tap but I've not run it since I pulled the valves.
What I meant about the crank trigger was me not seating it properly on the master spline and torquing down misaligned. Thinking about it it would have to be hanging off to do that. I'm not that careless
Out today so I'll try a fire up tomorrow... Don't hold yr breath