'84 1200 engine for a '82 GW

[Denver]

Believe you might be onto something Joe! 40 years or so ago put things together wrong when setting up the timing for the points, got 180 degrees out of time, reversed points & drove the damned thing. The hot set of cam's i put in, had NO pin in the end, to align with base plate, for a starting point, to set up the ignition's firing. Eventually figured out what i had done wrong, & fixed things back to where they belonged. Never thought about this again, till now. 176, or 174 degrees out of time, & reverse the ignition, do same thing???

 

[slabghost]

Length and number of teeth on the belt is not an issue if the teeth are correctly spaced.

 

[Denver]

:good: Exactly

 

[slabghost]

At issue here is the difference in stroke between the 1100 and 1200. Using the 1100 cams on a longer stroke motor will place open and close position of valves differently than the 1200 cams. check the offset of the lobe tips on both cams between intake and exhaust for the same cylinder. To get the most out of the 1100 cams you will need to compromise position slightly one way or the other.

 

[canuckxxxx]

Joe, when I had both engines apart I looked at an 1100 cam wheel and held it on top of a 1200 and lined up the keyways so I could see if the timing marks were in the same place. But I didn't look if the teeth lined up on both wheels. :head bang: Maybe the 1200 cam wheels have teeth offset slightly. I ended up using 1100 cam wheels...wonder if it would be different with 1200 cam wheels. :headscratch:

Does anyone have both wheels laying around that you could take a look at? :beg:
:thanks:
Brian

 

[joedrum]

no difference brian put that to rest

 

[ekvh]

Been fishing all day. Lots to catch up on. I run my hybrid about 8 degrees advanced. If I never posted how I did mine, I did the cam pulleys. I bought extra pulleys to attempt. I simply took a a smaller flat file and put the file in a vice. I then held the pulley in my hands and worked the correct side of the keyway until I opened the gap the equivalent of four degrees advanced. I then cut some pieces of tempered steel the same as the keyway. I tapped them in snug. The pulley holds them in place in the front and the keyway in the back. I have a couple thousand on them know and am pretty confident they will hold up.

I know, not real proper and all, but I just wanted to give it a whirl. It was going to cost at least a Bennie to have a machine shop do it. I can post pictures if you want to see how I did it. You can even call me crazy if you want.

Slab, I never thought of using the crank.

 

[joedrum]

wow i had forgotten that opcorn:

 

[canuckxxxx]

At the front of the 1200 service manual there are some specs.: Intake opens 10º BTDC, closes 40º ABDC. Exhaust opens 40º BBDC, closes 10º ATDC all at 1mm lift. So the cams are advanced as compared to the 1100.

My 1100 cams only have 48º duration vs 50º for the 1200. So with my setup, maybe I should shoot for Intake opens 9º BTDC, closes 39º ABDC. Exhaust opens 39º BBDC, closes 9º ATDC.

Joe and Eric, you guys are putting different cams and heads on 1200s all the time. What do you do about valve timing?

Brian

 

[Denver]

That will work, have to be more exact with 6, than four degrees. Know every G M V/8 i ever owned 60's & early 70's, had timing advanced to start & run better. Any way to advance the correct amount, will net the same result!!! crank should be easier, only one adjustment to make

 

[joedrum]

ok ..theres a stroke difference between 1000-1100 motor and 1200 motor ...when 75 cams are used in 1200 ..the piston catches the valve before it get home or coming out sheesh cant remember it right ... reason for slight piston knotching ...so its obvious cam timing is change a bit or whatever ...but we are talking circle here ..seems most all oldwing cams are 10 degrees overlap at tdc .. well to me if you go advanced machanically your doing cam ...or if in spark ...for me im set at tdc as i know all differences are split down the middle and valve overlap remains equal at tdc....to be honest i never seen one reason to change anything brian not one ...timing advance from iggy is more the answer id say ..... opcorn:

 

[Ansimp]

+1 changing valve timing will always be a compromise unless it is variable cam timing, variable ignition timing makes the most gains for the easiest investment.

 

[canuckxxxx]

Ansimp » Mon Jul 20, 2015 9:47 pm[/url]":t58w0gkz]
+1 changing valve timing will always be a compromise unless it is variable cam timing, variable ignition timing makes the most gains for the easiest investment.

The only reason I changed valve timing is because when I checked it, with a degree wheel it was not at factory specs. The cams were retarded by 8 degrees. The only thing I had to change it with was moving 1 tooth more advanced on the cam wheels. Which is way too much. I'm not finished with it. I intend to use offset keys to get me to closer to factory.

My thinking was wrong as which factory specs to use: I used the 1100 specs because I'm using 1100 cams but now I'm thinking I should use 1200 specs the whole rest of the engine is a 1200.

But I thought it was interesting and encouraging the way it performed after I changed it. The new, improved compression readings are still borderline low, so it is still not running at it's full potential, but it gives me a glimpse of how awesome it can be.

Brian

 

[dan filipi]

canuckxxxx » 13 minutes ago[/url]":2bwkw8bh]

Ansimp » Mon Jul 20, 2015 9:47 pm[/url]":2bwkw8bh]
+1 changing valve timing will always be a compromise unless it is variable cam timing, variable ignition timing makes the most gains for the easiest investment.

The only reason I changed valve timing is because when I checked it, with a degree wheel it was not at factory specs. The cams were retarded by 8 degrees. The only thing I had to change it with was moving 1 tooth more advanced on the cam wheels. Which is way too much. I'm not finished with it. I intend to use offset keys to get me to closer to factory.

My thinking was wrong as which factory specs to use: I used the 1100 specs because I'm using 1100 cams but now I'm thinking I should use 1200 specs the whole rest of the engine is a 1200.

But I thought it was interesting and encouraging the way it performed after I changed it. The new, improved compression readings are still borderline low, so it is still not running at it's full potential, but it gives me a glimpse of how awesome it can be.

Brian

Keep at it Brian, you're in new territory with this and doing great.

I'm thinking 1100 cam spec should be used but you know me, I'd have to try both :yes:

 

[ekvh]

I think you need to add 180 degrees for the duration numbers. The 1000 cams will cause the intake to hit as the piston comes to tdc. It's partly the lift, but it's also the placement of the valve, the angle the valve comes in on, and the 1200 piston shape, and the fact that the 1200 is stroked to come further out of the block. The Pistons on mine came out of the cylinder 0.040" at tdc. The 1200 valve faces come in closer to parallel to the piston face than the 1000. All are factors in the swap.

Which is best?? Only a dyno can tell to convince all. I like the torque moved down the curve. I was really nervous about doing it with mine, but so far it's safe.

The way I understand it, if you go more than five degrees, the exhaust piston will be closing BTDC rather than ATDC, which may cause reversion in the partially open intake. Might affect idle and low rpm. Mine must be very close to that right now. I have four degrees worth of spacing, but I also shaved my heads 0.025" which retards the timing a bit. Using the early cams, I don't think you can get around that, the cam's profile is the part we can't mess with a lot, or at all that I know of.

I'm thinking 9 degrees advance is as much as you want to go. The other factor here is that waste spark. It comes in on the exhaust stroke too, but if the intake is partially open when it fires it may give some popping if some of the new fuel is drawn across the intake to the exhaust. Too much and it could come back through the carbs, yes?? Timing at 10 BTDC is going to be close to touching it off when you decelerate and the advance comes back to 10 BTDC. I originally set my ignition timing at 5 BTDC for fear of this, but I am at close to 10 BTDC now.

Advancing the cams increases compression by closing the intake sooner and allowing more time and therefore distance for the piston to compress the mixture, but it also opens the exhaust valve the same amount earlier and so there are losses to the expansive push of the mixture on the piston on the way down. That's where we lose at upper rpm.

Take everything I say with a grain of salt and know that I'm just a hack trying figure this out. It's a late-in-life hobby for me, and I rely on correction from people wiser than me. I have been wrong before..........a LOT.

 

[canuckxxxx]

I just went out to the garage and took the crank belt wheels off the front of the 1100 so I could see how it is put together. As Dan said, once the bolt is out the timing wheels slide right off. Both wheels are the same. The key is centered on a cam teeth and the wheels are the same front to back. So you could put them in front to back and interchange wheels and they would give the same timing.

The big thing to me is that the key seems to be integral to the wheel so there is not the option to make an offset key to change cam timing. I wondered about the keys because I went to the Western Honda parts fiche and could not find a key.

crankshaft belt wheel 2

• canuckxxxx
• Jul 21, 2015

You can see how the keyway lines up with the center of the teeth.

crankshaft belt wheel 1

• canuckxxxx
• Jul 21, 2015

So now I'm back to thinking of getting or making offset keys for the cam wheels. That way I don't have to change the cam or cam wheel keyways.

Brian

 

[joedrum]

opcorn: neat... to me the cam just has new numbers ...seems if mark out at head is on mark cam has to be centered there when at tdc mark also ....this leaves all the difference away from tdc spot....i do agree this changes numbers on cam .. making overlap less and everything else also .....

 

[canuckxxxx]

Another trip out to the garage to measure one of the 1200 cams I have laying around to see that the diameter of the part where the cam wheel goes is 20mm, the key is 4mm wide and the total depth of the key is 4.5mm.

So, doing a bit of math: :read: the circumference of the cam is 20mm x pi = 62.83mm. For me, in order to change my timing from 3º ATDC for intake opening to 9º BTDC I need to advance the cam by 12º. 12º / 360º x 62.83mm = 2.094mm (.08"). So I need to buy or make a couple of keys that are offset by 2.1mm or .08".

I'm having trouble visualizing how the whole thing will go together. If the offset keys are put in then would I install the belts according to manual. That is, turn crank to TDC and install belts so arrows on cam wheels line up with the marks on the heat shields? Or would the arrows be shifted by the amount of the offset keys? :headscratch:

Brian

 

[canuckxxxx]

canuckxxxx » Tue Jul 21, 2015 7:04 am[/url]":1naw1j4r]
Another trip out to the garage to measure one of the 1200 cams I have laying around to see that the diameter of the part where the cam wheel goes is 20mm, the key is 4mm wide and the total depth of the key is 4.5mm.

So, doing a bit of math: :read: the circumference of the cam is 20mm x pi = 62.83mm. For me, in order to change my timing from 3º ATDC for intake opening to 9º BTDC I need to advance the cam by 12º. 12º / 360º x 62.83mm = 2.094mm (.08"). So I need to buy or make a couple of keys that are offset by 2.1mm or .08".

I'm having trouble visualizing how the whole thing will go together. If the offset keys are put in then would I install the belts according to manual. That is, turn crank to TDC and install belts so arrows on cam wheels line up with the marks on the heat shields? Or would the arrows be shifted by the amount of the offset keys? :headscratch:

Brian

Wait, I made the same mistake as before; :head bang: if I want a 12º change at the crank then I only need a 6º change at the cam wheel. So only 1mm offset at cam key. Yikes the chances of a screw-up are big. :shock:

 

[joedrum]

yep they are brian ive had this stuff going through my head since the early days of hooch