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Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
OK... I got a bit more work done last night, but no fancy photos to post.
First up, I measured out the volume of the combustion chambers (24.5cc) and the piston domes (12.5cc) and worked out my static compression ratio. I think my head gasket is .040" and the piston sits .040" below the deck and so that brings my static compression to 11.7:1. My dad thinks the gasket might be .020" and the piston clearance is .020" as well and that's more like 13:1. Even if we split the difference, those seem to be some pretty healthy numbers. Certainly a fair bit better than the 9.3:1 offered by the stock setup.
After making the appropriate measurements, I assembled everything in order to check piston-to-valve clearances. Turns out it's tight. VERY tight. I laid down a piece of solder onto the intake valve pocket in the piston and after turning the crank over a few times (I felt the valve contact the solder) I pulled everything back apart. Unfortunately, the solder was severed by the valve. I only found out after the fact that I should have been using flux-core solder for this and so I'll need to repeat the test this evening (I'll use playdough this time). I only tested the left side as well. The right side showed no signs of contact as the carbon layer on the piston was undisturbed. Furthermore, I had the intake tappet clearances set to .003" but the cam manufacturer says to use .004" on both intake and exhaust. So that may be a contributing factor.
Finally, the .020" that was skimmed from the head doesn't seem to have made a great deal of difference to the cam timing, but I've got a degree wheel and now that I'm sure of TDC, I'll be sure to verify it. The timing card from the cam says intake opens at 16° BTC and the exhaust should open at 55° ABC and so I know what I should be aiming for.
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
OK.. so I just got this PM from a member on a different board that I frequent. Your guys' thoughts? How much of this are legitimate concerns that will apply to my situation? Don't get me wrong, I know it's often best to err on the side of caution, but I've known quite a few alarmists in my day I'm not usually the type of guy to take advice only from a single source. Evidence is what sells me. Lacking that, a little corroboration helps.
[quote author=guy on other forum]Dude...
even w/ my limited exp "40yr of bikes"... I SMELL disaster.
You don't "split the dif" on determining CR...or ANYTHING!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!
plan on running pump gas?... redefine "better" CR than stock.
Your counting on copper sealer to get you by on tha BOTCHED skim job??????? GOOD LUCK!!!!!!!!!
WHOEVER did the job OWES you a "new head' and work done RIGHT. PERIOD
You DON'T only do ONE side determining valve clearance...PERIOD... EVER ...'cause the crown carbon was "undisturbed"??? Tick tick tick...KABLOOOY!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!
Why check it w/ out AT ALL w/ out PROPPER tappet clearance set already?????... your learning curve involves recipricating metalic parts that are VERY unsympathetic, that you are just learning.
READ READ READ.
SOLDER?...shoulda used RESIN CORE???... playdough???... USE PLASTICINE "clay"!!!!!!!!!!!!
Those rockers w/ the BIG grinding fuerels in them are just WAIT'N for stress risers to ATTACK...
you CAN'T say "polishing" has relieved that concern... the HUGE valleys are STILL there.
I SALUD your verve!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
but as I said... that engine has LITTLE grace for anything but methodical, consistant and "RIGHT"... or it goes... POP!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!
If you wanna do RACEY things to your motor...
check out the sites of people that ALREADY RACE these motors. Otherwise, the learning curve WILL get ya and you might as well be dumping $$$ in a hole in the back yard.
Hows your oil pump?
Wisdom says, seek those that have proceded you.
It is not my endevor to call you out 'publicly'... but to steer you tword a FUN time and result, of you FINE obsession!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!
SALUD!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!! !!!!!!!!![/quote]
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
My machinist quoted be at between $3.50 and $4.00 per valve to back cut them so they'll be dropped off tomorrow. I'll get his opinion on the head milling job as well, just to be sure the scratches in it don't need to be lapped out.
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
Here is some info from the guys that race these engines. It give the piston to valve clearance that they recommend:
http://www.eurospares.com/engine.htm
I don't understand why using resin core solder makes any difference...Plastic modeling clay is easy to measure. If you cut the solder I would say the valves are too close to the pistons. Also why can't you measure the thickness of the head gasket? If your calculations are correct and you will have 12 - 13:1 compression ratio you will need to run better than premium. You will need racing gas or it will ping. That won't be very fun when you want to go for a ride and need to fill up when you are on the road. You may need to use a thicker gasket at this point.
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
I gues guy on other forum want's perfection or nothing (can't beat a stock bike blah, blah, blah) ;D
Doesn't have a clue by the sound of it, NO ONE races CB360's and the only one I've ever heard of was a 420cc? in Australia
Actual compression pressure will be a lot lower beause of more valve overlap
Just stick a compression tester on it when it's all done
Anything below 225psi is fine, although you may have to mix some race gas with 93 octane or mess with jetting to use E85
You want about 210~215psi, it's a small chamber so will be fine
Personally, I haven't bothered to work out a static CR for at least 30 yrs, it's an irrelevant number
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
Thanks for the info guys. That's pretty much what I figured but it never hurts to double check.
cyclhed, I'm not entirely ruling out the possibility of having to use race gas, but I'm pretty sure I'll be OK. I'm not quite that close to the ragged edge. If I hear any pinging I'll be sure to get some higher octane stuff ASAP. As pj mentioned, static compression numbers are just that... only numbers. They're good for getting an idea of what the engine is doing and how it will perform, but it's the dynamic compression that really matters and with a higher duration cam (like the one I have), I'm not too concerned about the compression just yet. Also.. the 360 engine tends to run a bit cool anyway (at least mine does).
While we're on the topic of compression ratios, I did go back and remeasure everything to make sure my information was correct and... it wasn't. The head gasket measured out at between .032" and .036" depending on where the calipers got it but almost all of my readings were on the thicker side of that scale. For these purposes, I'm going with .035" as the thickness of the head gasket. The pistons sat exactly .020" below the deck at TDC and I'll stick with the volumes of my chamber and piston domes at 24.5cc and 12.cc, respectively. Calculated static compression is 11.99:1. I'll just call it 12:1.
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
A couple of observations:
That OP is almost right but is acting like a complete ass, so it's hard to validate much of what he said. Rockers should ideally be polished and then shot peened to replace the hard "skin" but I never do and the only time I broke rocker arms is when a valve head or cam chain broke first.
That head is not perfect, but with any regular gasket it should seal just fine. It's a shame about that gouge/drag mark, but you can always have a touch more skimmed off to clean it up if it does leak.
0.5mm should not make the static CR 12:1 unless stock was 11:1. .035 head gasket is thinner than stock. I'd double check that with the head bolted down. Stock combustion chamber (net) is around 20-22cc. Yours appears to work out at around 16cc. That's 4-6 less than stock and .020 is less than 2cc. Something off in the math or he machined .060" off the head. I suspect the numbers may be off. Check the head height overall and ask PJ to check a stock head to confirm what came off.
Valves should be checked with prussian blue to see how wide the seat is and then the top surface should be trimmed to bring the seat widths back to spec. That is what PJ referred to as back cutting.
I would not undercut the stems at the head to try to improve flow unless your machinist really is good and you can afford to replace valves and broken motors. We won't do it on a motor unless I know it will be stripped and valves replaced regularly. That may be a little cautious but I hate stock Honda valves dropping their heads and stress raisers increase that possibility.
PJ is spot on with his porting comments. Just clean up any obvious lumps but try not to take much metal out. Get Bell's book for sizes around the guide and into the bowl.seat area.
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
Thanks, teazer. I appreciate the extra information.
A few extra things to be aware of though, which may affect your analysis?
I'm running aftermarket pistons specifically designed to increase compression and so is this a likely candidate for the excess compression or was that already taken into account?
Also, I'm running with Kibblewhite +1mm valves and the stems have already been undercut (from the manufacturer) and so I won't be messing with that portion at all.
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
Matt, Thanks for the details. I managed to miss the reference to the valves already being that way and the high Comp pistons. That may explain it. They must have huge lumps on the top. That could also explain the lack of piston to valve clearance.
Is the problem around the edge or all across the pocket?
Cams with higher lift and more overlap also contribute to the clearance issue.
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
Yeah... the pistons are fairly large....
For clearance issues, I'm not too sure yet. I have more testing and verification to do before I know for sure.
Here's a pic of the clearance testing prior to the head milling and new +1mm valves:
To me, it looks like pretty good clearance and I don't think .020" skimmed from the head would account for a clearance issue now and so my instinct is telling me part (or maybe all?) of the problem may be the larger valves...
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
Bigger valves obviously reach out further on the piston crown but they also sit higher in the head - I guess that's lower when the head is the right way up. I usually have the valves recessed slightly to regain that lost clearance.
BTW the think about rosin core solder is that it's usually easier to squash, so less load on valves.
How much taller are the crowns and are they larger bore as well? Both combined would start to make sense for the compression. If that's the case, you might want to get squish band right and relieve the chamber slightly to get the CR where you want it.
Squish creates turbulence and faster burn and that reduces the probability of detonation.
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
I've had to do some major cutting to fit oversize valves and maintain installed height close to stock.
You did measure original installed height and set new valves to withing 0.010" or so?
You may also need to flycut combustion chamber, measure the angles of piston. and chamber
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
The crown (I'm going from memory here) is .060" higher but no larger in bore. The valve cuts sit .020" deeper than stock to accommodate lift and duration from the cam, but I wasn't expecting larger valves when I had the pistons made.
The thickness of the squish band is currently .055". I know that's pretty much right on the upper limit of what's useful and if I can maintain clearances, a thinner head gasket isn't out of the question.
As far as valves go, I've no special measurements or adjustments just yet. I (foolishly?) assumed the machinist would set things up correctly. Where should I start?
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
I'd start by measuring valve to valve clearance and valve to piston clearances. Then I'd have the valve pockets in the pistons opened up to clear the valves at the outer edges. add say 1.5mm clearance there on the edge of the valve.
The valve seats need to be cut again to pull the valves back slightly to get them back to the correct height in relation to the rockers and cam and valve springs. Measure valve spring installed height too and that will provide a baseline to work from.
Intake valve clearance is important but the exhaust is critical near TDC on overlap. It is usually exhaust valves we have intimacy problems with.
That squish is a little large. What I usually do is to shorten the barrel to bring pistons up to zero deck height and use a 40 thou gasket to set squish. recessing the valves will increase combustion chamber volume more than you might expect, so it should all work out.
.060 taller is a heck of a lot larger piston though for a street motor. I like flat tops/low domes and low flat chambers to get compression where I want it.
Re: '77 CJ360T (Café SOS) - Head and Valve Work Complete
teazer said:
I'd start by measuring valve to valve clearance and valve to piston clearances. Then I'd have the valve pockets in the pistons opened up to clear the valves at the outer edges. add say 1.5mm clearance there on the edge of the valve.
The valve seats need to be cut again to pull the valves back slightly to get them back to the correct height in relation to the rockers and cam and valve springs. Measure valve spring installed height too and that will provide a baseline to work from.
Intake valve clearance is important but the exhaust is critical near TDC on overlap. It is usually exhaust valves we have intimacy problems with.
That squish is a little large. What I usually do is to shorten the barrel to bring pistons up to zero deck height and use a 40 thou gasket to set squish. recessing the valves will increase combustion chamber volume more than you might expect, so it should all work out.
.060 taller is a heck of a lot larger piston though for a street motor. I like flat tops/low domes and low flat chambers to get compression where I want it.
Thanks, man. When you mean valve-to-valve clearance, where are those measurements made?
Also... the valves have already been slightly recessed into the head as part of the work that was recently completed, so no problems there, but I'll go ahead and double-check valve-to-piston clearances. It seemed the problem was only on the intake side, but I'll get some concrete numbers.
Next, shortening the barrels isn't an option just yet, but I'll definitely add it to the todo list the next time I have the motor apart. Running with open intakes will probably mean new rings every 5,000 miles and so I expect to have this thing cracked open again over the winter... lol
Finally... for flycutting the pistons to accommodate the larger valves... it's this precision kind of work or something I can do with a Dremel?
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