Not starting after new cams installed

[GaryZ]

Ok guys, the new cams are installed and the engine is back in the frame. I connected the battery and cranked it over. The front cylinders are firing, the back cylinders are not. The back cylinders are spitting out of the carbs.

 

I checked and found no compression on those cylinders. I removed the valve covers and rechecked the cam timing. It looks right with T1 = back cams aligned and T2 @ 430 degrees counter-clockwise and front cams aligned.

 

Any ideas as to why the back cylinders are not firing?

[bkuhr]

suspect no compression = valves not closing completely, check valve shim gap

[dingy]

Besides what Bkuhr said, another guess could be exhaust & intake cams swapped.

 

Gary

[bkuhr]

If I recall correctly,

Rear head #1TDC @T1 intake and exhaust cam lobes point toward each other at about 60 deg from straight up.

Front head #2TDC @T2 intake and exhaust cam lobes point away from each other at about 60 deg from straight up.

 

If intake and exhaust cams swapped, suspect lobes would point opposite above

[GaryZ]

Besides what Bkuhr said, another guess could be exhaust & intake cams swapped.

 

Gary

 

I just checked and the cams are in the correct location.

[GaryZ]

suspect no compression = valves not closing completely, check valve shim gap

 

The valve buckets are following the cam lobes.

 

What would be another way to verify the valves are closing?

 

I will be checking clearances tomorrow . . .

[bkuhr]

Apply about 60 psi from air compressor to sparkplug hole (I use hose from compression tester and leakdown gages set) with piston at TDC. #1=T1, #3= I'd have to get the book out for degree's rotation from #1. Hold crank with wrench to keep air from pushing piston down

 

Listen for where air blows out

 

carbs= intake not closed

mufflers=exhaust not closed

case breather=piston ring blowby. I have about 20psi ring blowby and was good

around head=head gasket/heads not tight,etc

[BradT]

Just double check and make sure. When installing cams at the T2 position, you are lining up the LARGE holes (NOT small holes) on the cams.

 

Also if you installed the Chain Tensioner it will rotate the engine so double check your T2 mark before installation of cams.

 

Hope you find the problem.

 

Brad

[GaryZ]

Gentlemen,

 

Thank you for all of the suggestions. This time BradT was closest to the answer.

 

I aligned the front cams correctly to the BIG hole, unfortunately I also aligned the rear cams to the BIG hole!

 

Don't know how I managed, but, at least I will sleep tonight knowing what's wrong.

 

Anybody think I can fix this with the engine in the frame?

[dingy]

Can you reach rear cam tensioner.

 

You will need to remove it, Then reset cams, Then reinstall tensioner.

 

It sets between the rear exhaust headers.

 

If you can get tensioner out, it is doable.

 

Also be careful when reinstalling tensioner. I had one of the wings break of on my front head causing an initial oil leak. Torque down by going back and forth several times.

 

Might also need a new gasket for tensioner. I ended up making one.

Gary

[Venturous Randy]

I just hope yopu did not bend any valves when you had it out if time. Now, don't that just make you sleep better.

RandyA

[GaryZ]

I just hope yopu did not bend any valves when you had it out if time. Now, don't that just make you sleep better.

RandyA

 

Thanks, I needed that . . .

[dingy]

I just hope yopu did not bend any valves when you had it out if time. Now, don't that just make you sleep better.

RandyA

 

 

Please say that you cranked engine over by hand through several revolutions first !!

 

 

Gary

[BradT]

Gary Did the same thing but I lined up all the small holes. Backfired so bad the carbs popped out of the rubber boots. Does not bend the valves as mine started up and actually ran. (didn't sound pretty)

 

Yes you can rotate the cams in the bike. Pretty sure you do not need to worry about the cam tensioner. Once you remove cam caps I think you can rotate the cam tooth by tooth on the sprocket, can't remember if you lifted the cam sideways a bit but it was it rotating one tooth at a time. Getting the valve covers back on is harder.

 

Glad you found it.

 

BRad

[Karl C.]

Not wanting to steal thread but this really made me have a question: is the 1200 in the 83 venture a clearance engine? Well I guess I should ask is all the gen 1 clearance engines..

[dingy]

 

Yes you can rotate the cams in the bike. Pretty sure you do not need to worry about the cam tensioner. Once you remove cam caps I think you can rotate the cam tooth by tooth on the sprocket, can't remember if you lifted the cam sideways a bit but it was it rotating one tooth at a time. Getting the valve covers back on is harder.

 

 

BRad

I am not saying your wrong Brad, but I just had an engine apart and when I tried to even re-shim valves without an official valve tool, I had to release the cam tensioner in order to get enough slack in the chain.

 

The purpose of the tensioner is to remove all the slack so there is no slop in chain.

 

The tensioner is a one way ratcheting mechanism, it has to be pulled out of the engine in order to release the tensioner rod holding prawl.

 

Even if he unbolted the gear from the cam, as soon as there is any slack in cam chain the tensioner is going to extend via its spring, then making it impossible to reattach gear.

 

Just my humble opinion, but I did stay in a Holiday Inn a couple of times.

 

Gary

[GaryZ]

Not wanting to steal thread but this really made me have a question: is the 1200 in the 83 venture a clearance engine? Well I guess I should ask is all the gen 1 clearance engines..

 

Clearance engine?

[BradT]

Karl not sure, my rebuild was on a 86 1300 engine.

 

I thought he was refering to clearance in the valves and piston on the 1200 vs 1300 engines.

 

Gary That is why I said I can not remember but I do not remember playing with the tensioner while the engine was in the frame. I do remember fighting with it while the engine was on the ground, thinking how the heli would you do this with the engine in the bike.

 

BRad

Edited May 6, 2010 by BradT

[dingy]

Not wanting to steal thread but this really made me have a question: is the 1200 in the 83 venture a clearance engine? Well I guess I should ask is all the gen 1 clearance engines..

 

 

WTF is a clearance engine ?

 

There is a lot of clearance between the back end of a 1st gen and the front end of a 2nd gen when racing I guess.

 

Gary

[bald josh]

a clearance engine is one when the timing belt or chain breaks it doest destroy itself, there is clearance between the pistons and valves in any position any of those may be in, non clearance, and your pistons destroy valves and themselves...id like to know this too!

[GaryZ]

There is a lot of clearance between the back end of a 1st gen and the front end of a 2nd gen when racing I guess.

 

Gary

 

 

:rotf:

[dingy]

a clearance engine is one when the timing belt or chain breaks it doest destroy itself, there is clearance between the pistons and valves in any position any of those may be in, non clearance, and your pistons destroy valves and themselves...id like to know this too!

 

Then, no it is not a clearance engine.

 

Gary

[GaryZ]

OK all you Venture Valve and Cam specialists, I fixed it!

 

I made the mistake of using the BIG hole to align all 4 cams. The result was the front cylinders fired and ran, the back cylinders would open the intake valve and immediately open the exhaust valve. No compression and only an occasional backfire through the exhaust.

 

BradT aligned all cams to the small hole and the rear cylinders ran, the front cylinders backfired through the carbs. All I can say is . . . That must have been exciting.

 

Anyway, I left the engine in the frame to try and fix this error. The carbs had to come loose in order to make room to remove the rear valve cover. I left them hooked to the throttle/choke cables and simply moved them around. I removed two cam cap bolts and the cam chain guide from between the cam gears. All of the other cam caps stayed installed. I had not installed the exhaust coupler or rear brake master and was able to remove the rear exhaust manifold. This made it much easier to remove the cam chain adjuster. The manifold could have stayed installed, I simply took advantage of the situation. This set-up gave me slack in the cam chain.

 

The exhaust cam was easy to reposition by walking the cam chain around the cam gear. The intake cam was a different story. When properly aligned at T1, the intake cam is opening valves. Rotating the cam with bare hands is not possible. I used a 7/8" open-end wrench on the hex shape between cam lobes and was able to rotate the cam with some power. I walked the cam chain to the correct position one tooth at a time.

 

A friend held the 7/8" wrench and the cam aligned while I stabbed the cam chain adjuster. I re-assembled the bare minimum for the beast to start and it fired on all 4 cylinders immediately. Man, this thing is loud in the garage with straight pipes!

 

Thanks to everyone for all the help and comments.

 

 

GaryZ

[dingy]

I know that now you feel much better.

 

 

Gary