pistons and valves contact

[2cams70]

Whenever you do these kind of set up activities it's entirely normal to expect to have the head off and on a couple of times. It always pays to have a couple of head gaskets on hand that are of the same type and thickness as the one you intend to finally use. Even though it may be new I would not reuse a head gasket that had previously been installed and compressed.

[checkrail]

Good News! Have removed the head and I'm glad to say there is no sign of any damage or contact, so what caused the locking up?
After cleaning the head and block I'm going to fit the cams and shims on the bench and see what happens.
John

[Europa88]

Good News! Have removed the head and I'm glad to say there is no sign of any damage or contact, so what caused the locking up?
After cleaning the head and block I'm going to fit the cams and shims on the bench and see what happens.
John

That is good news

[promotor]

Good News! Have removed the head and I'm glad to say there is no sign of any damage or contact, so what caused the locking up?
After cleaning the head and block I'm going to fit the cams and shims on the bench and see what happens.
John

My advise would be to rotate the cams while the head is off (head upside down) to make sure you can get full rotations of each cam (both in the direction of the running engine rotation ie clockwise when viewed from the front of the engine) - however, be VERY careful and watch what each valve is doing in relation to its nearest valve - you will need to turn one cam a small amount and then turn the other cam a little to avoid valve-to-valve clash. If you don't think it's possible for valves to avoid each other, don't force anything.

Make sure the head is supported and that no damage will come to it, particularly on the head gasket face.

Satisfy yourself that nothing is binding in the valve train. You may have some other issue causing the problem rather than valves hitting something. You might have something in between the valve springs.

You may then want to check that all valves are seating properly and that you haven't bent any valves : put petrol either in each port or fill the chamber (with both relevant valves closed and covered over with fuel) and see if fluid leaks past the fully closed valves.

If everything seems OK and once the head is on, everything is timed up and you manage to rotate the engine without problems the final test is to see whether you have compression on each cylinder - you should notice resistance when turning the engine over by hand (spark plugs fitted), the resistance being caused by the shut valves and the pistons compressing the air in the cylinders. You will get a little bit of hissing where air passes the piston rings which is normally a sign of some compression at least.

Finally, double check your crank and cam timing marks before firing up!

Good luck!

[checkrail]

Thank Promotor for that very detailed reply I will try all that very carefully

John

[promotor]

Thank Promotor for that very detailed reply I will try all that very carefully

John

No problem - hopefully this photo shows what is going off in a twincam engine and how close to valve clash these engines can be if one cam moves too much independently of the other. This photo was taken with the head installed on a block with the cams and crank set at the correct timing positions but without the piston and rod installed, looking up the cylinder bore from the crankcase.

[HCA]

Hi all, just replaced the head after renewing the gasket .......
.....If I turn the cams using the sprocket bolts with the chain disconnected they will jam as one of the lobes presses down on the tappet,

I am coming into this thread new, so maybe I have missed something pertinent. I am by no means an expert, but why would you even think of doing the above?

[Hawksfield]

Hi HCA
My thoughts as well
I think a study of the twincam is required.
Hope he has not done any damage

[billwill]

When I was young and didn't understand about valve & pistons on a twin cam.

[checkrail]

HCA and Hawksfield, have you read all my earlier posts?

John

[HCA]

No, I confess that I have not!

I only opened this one as I am in the process of sizing pistons for BDA rods I am building into a 1700 motor, and presently I am consumed by the possibility of anything fouling or being fouled...

As I said, there might be something pertinent that I missed for which I apologise profusely! It was the 'turning the cams with the chain disconnected' that made me wince a tad

[checkrail]

I've found out that the jamming is caused by the different thicknesses of the tappet shims. Because I am have'nt to start from square one after loseing the original sizes.
I am still working on the bench

John

[Europa88]

The shims must be seriously muddled to make one or more of the coil springs to compress out to maximum and lock the cam

[checkrail]

Replaced the head with new gaskets, and spent days and days swapping the buckets and shims around to get the cams to rotate indepently without the chain connected.
The problem is when a cam lobe makes contact with the bucket the cam locks up, I've smeared them with Graphogen, they are not worn just rubbing marks as they have revolved.
I'm wondering whether to get a new set

John

[HCA]

Please, please, what are you doing?

You cannot and should not rotate two cams and a crankshaft independently of each other, especially so with a hemi engine. Somewhere in their independent cycle you will hit pistons and/or have valve clash. You have been told this earlier in your post. Why do you not heed it?

For heavens sake, examine the followers and shims, replace if necessary, adjust the tappets properly, re-install the timing chain with the crank and camshafts properly aligned, and then ask the knowledge base here about the fine tuning before you do some irreparable damage.