Pride does come before a fall

[david johnson]

After all the work to set up the rebuilt engine, I took it out for a good run today keeping down to 2250 revs max.After 10 miles something happened and it started to misfire badly. I nursed it home, only just, for 6 miles.Nothing visible wrong no overheating, though the brakes had seemed rather poor. I neglected to check the oil pressure.I lifted off the rocker cover with some sixth sense and found two push rods completely free, one bent slightly. The valves look ok, not bound, collets in place. The adjusters are not disturbed and there is no way the straight push rod would go back, without winding them back

Does anybody have any thoughts. Are the rods not strong enough for the new valves and higher compression engine.Am I likely to have done any serious damage nursing it home. Thanks David Johnson

[Guest ntc]

David

You have PM

 

Neil

[Chris Mountford]

Hi David,

 

had an experience like this many years ago with a 'performance' camshaft from one of the performance TR specialists.

 

The car was a '125' spec CR TR6. The symptoms were;

 

Broken rocker arms when the engine got warm!

 

I think we killed 3 before we found out what the problem was. It turned out that the bottom spring seat needed to be removed (no one said) because as the valve springs expand with temperature, the clearance disappears and they become 'coil bound'. When they cool the clearance reappears. Our initial thoughts were that the valve timing was out and went down that route initially. We were stunned to see 25 year old rocker arms broken clean in two across the bearing. Anyhow adequate clearance was given by removing the lower valve spring seat (the bit that keeps the inner and outer valvesprings concentric).

 

We did the supplier R & D on that one along with who knows how many others. Perhaps we should have gone into the thermal coefficient of expansion and calculated the appropriate 'cold' clearance when we fitted the parts? live and learn.

 

Bit long winded explanation, but sounds like remarkably similar end result.

 

Hope this is of use.

 

Chris

[rpurchon]

After all the work to set up the rebuilt engine, I took it out for a good run today keeping down to 2250 revs max.After 10 miles something happened and it started to misfire badly. I nursed it home, only just, for 6 miles.Nothing visible wrong no overheating, though the brakes had seemed rather poor. I neglected to check the oil pressure.I lifted off the rocker cover with some sixth sense and found two push rods completely free, one bent slightly. The valves look ok, not bound, collets in place. The adjusters are not disturbed and there is no way the straight push rod would go back, without winding them back

Does anybody have any thoughts. Are the rods not strong enough for the new valves and higher compression engine.Am I likely to have done any serious damage nursing it home. Thanks David Johnson

 

i had similar problem with my new cylinder head.

same valve, happeneed about 3 times.always when car not run for a few days.

and always after about 5mins driving from cold.

cause lack of oil, sticking/binding valve guide.

i fitted my own valve guides.normal cast ones from moss, but i had to buy 2 sets and select the

the best fit.some were too tight.i used the ones which were slackest.and that was using old valves.

and before any one posts a reply,yes i have the correct sized reamer.

didnt do it after apx 100 miles

 

road side repair.use the dip stick and try get some oil onto valve stem through the springs.

turn engine over until the other valve is down,

lever the valve down with the rocker using a screw driver/spanner. and put pushrod back in.

no need to undo adjusting screw.

 

i didnt bend a pushrod. if youve fitted any kind of oil seals on the guides i take them

of untill youve done a thousand miles.and if you have bronze guides it will sort it self out

after 10,000 miles.

richard

[Guest ntc]

Hi David,

 

had an experience like this many years ago with a 'performance' camshaft from one of the performance TR specialists.

 

The car was a '125' spec CR TR6. The symptoms were;

 

Broken rocker arms when the engine got warm!

 

I think we killed 3 before we found out what the problem was. It turned out that the bottom spring seat needed to be removed (no one said) because as the valve springs expand with temperature, the clearance disappears and they become 'coil bound'. When they cool the clearance reappears. Our initial thoughts were that the valve timing was out and went down that route initially. We were stunned to see 25 year old rocker arms broken clean in two across the bearing. Anyhow adequate clearance was given by removing the lower valve spring seat (the bit that keeps the inner and outer valvesprings concentric).

 

We did the supplier R & D on that one along with who knows how many others. Perhaps we should have gone into the thermal coefficient of expansion and calculated the appropriate 'cold' clearance when we fitted the parts? live and learn.

 

Bit long winded explanation, but sounds like remarkably similar end result.

 

Hope this is of use.

 

Chris

Hi Chris

Good reply but Pete Burgess knows how to build a cylinder head

 

Neil

[Mike C]

David,

Are you certain the two pushrod end spheres were seated properly in the cam followers when the tappets were adjusted?

If the engine turned over cleanly by hand before it was initially started I don't believe running it for 10 miles at 2500 rpm should heat up anything enough to seize or cause any valve coils to bind up and jam due to revving.

Were the freed pushrods both from inlets?,exhausts?, or one of each?.

Assuming the pushrod end spheres haven't come loose and fallen into the engine-which may require a partial stripdown-,I'd certainly have a close look at all the rocker gear before I restarted the engine,including checking it for damage then rotating the engine several times to open and close each valve in turn,noting if any particular adjustment screws seemed to require more adjustment than the others.And if all the adjusting screws require to be backed right off to get the correct clearance, the chances are the pushrods are too long and new shorter ones will be required to suit the higher compression head.

Regards,

[david johnson]

Thanks for the replies. I will have to get to the bottom of it. Does anybody think that I may have done real damage? I suspect not - but then .....

 

Thanks

 

 

David Johnson

[PJM]

If you think it through logically provided the push rods were sitting clear of the rockershaft and rockers the valves would have been closed so the pistons would not hit the valves. The pushrods would have been travelling up and down, flopping around, the rockers would have been doing nothing, the valves would have been held closed by the springs.

 

The only likely damage would be due to additional stress because the exhaust gases had nowhere to go due to the valve not opening. If one cylinder only affected for both the inlet and exhaust then probably no damage at all, so I think the answer is it depends which valves were affected.

 

A good check of all the rocker gear, pushrods etc should be carried out to be certain.

 

You could get hold of a dye penetrant test kit and checking for cracking but if you are really concerned get them checked or changed.

 

So which valves were affected?

[Mike C]

David,

 

I agree with PJM.The only real damage in this situation would be caused by a valve hitting a piston.If this didn't happen when you turned the engine over on the starter then I doubt that this would happen at 2500 rpm as, even with over length pushrods, valve float is not a problem at this low engine speed.The bent pushrod was probably not bent by hitting a piston-might have been a cam follower once it was freed.Once the pushrods were freed from the rockers the valves would close and be largely immune from any damage.

 

Look at the rocker and valve in the position of the bent pushrod.If they look OK -not cracked or bent respectively -then the engine is probably OK.

A compression test will show if the valve face has been bent,preventing the valve from sealing against its seat.

Maybe for peace of mind remove all the push rods and check them.You need to reinstall them in the same location they were removed from(I normally do this by punching 12 holes in a cardboard box to hold them in place).If you purchased a modified head, you may want to take the pushrods back to the head supplier to confirm that they are the correct length.

 

You were lucky this didn't happen at 6,000 rpm.Hope all goes well.

 

Regards,

[Richard71]

i had similar problem with my new cylinder head.

same valve, happeneed about 3 times.always when car not run for a few days.

and always after about 5mins driving from cold.

cause lack of oil, sticking/binding valve guide.

i fitted my own valve guides.normal cast ones from moss, but i had to buy 2 sets and select the

the best fit.some were too tight.i used the ones which were slackest.and that was using old valves.

and before any one posts a reply,yes i have the correct sized reamer.

didnt do it after apx 100 miles

 

road side repair.use the dip stick and try get some oil onto valve stem through the springs.

turn engine over until the other valve is down,

lever the valve down with the rocker using a screw driver/spanner. and put pushrod back in.

no need to undo adjusting screw.

 

i didnt bend a pushrod. if youve fitted any kind of oil seals on the guides i take them

of untill youve done a thousand miles.and if you have bronze guides it will sort it self out

after 10,000 miles.

richard

 

If you suspect the problems lies with the valve guides, then maybe fitting an external oil supply to the rocker/valve gear for the first 500 miles would help.....just a thought.

 

Richard.

[Guest ntc]

The camshaft that you fitted does require matching double valve springs I assume you supplied these to Peter

 

Regards

Neil

[Guest ntc]

David,

Are you certain the two pushrod end spheres were seated properly in the cam followers when the tappets were adjusted?

If the engine turned over cleanly by hand before it was initially started I don't believe running it for 10 miles at 2500 rpm should heat up anything enough to seize or cause any valve coils to bind up and jam due to revving.

Were the freed pushrods both from inlets?,exhausts?, or one of each?.

Assuming the pushrod end spheres haven't come loose and fallen into the engine-which may require a partial stripdown-,I'd certainly have a close look at all the rocker gear before I restarted the engine,including checking it for damage then rotating the engine several times to open and close each valve in turn,noting if any particular adjustment screws seemed to require more adjustment than the others.And if all the adjusting screws require to be backed right off to get the correct clearance, the chances are the pushrods are too long and new shorter ones will be required to suit the higher compression head.

Regards,

 

You can also shim the pillars

 

Regards

Neil

[david johnson]

I think with the rockers appearing free, its just that the standard push rods are not strong enough for the stronger valves springs and high compression. One has bowed and popped out the other just bent. Ill fit stronger push rods, after having checked everything.Thanks for help David Johnson.

[Guest ntc]

I think with the rockers appearing free, its just that the standard push rods are not strong enough for the stronger valves springs and high compression. One has bowed and popped out the other just bent. Ill fit stronger push rods, after having checked everything.Thanks for help David Johnson.

 

Hi David

The std rods are fine for what you have done providing they are strait (roll on a piece of glass) ,have you measured the gap between the valve spring coils at full lift?

 

Neil

[jerrytr5]

I think with the rockers appearing free, its just that the standard push rods are not strong enough for the stronger valves springs and high compression. One has bowed and popped out the other just bent. Ill fit stronger push rods, after having checked everything.Thanks for help David Johnson.

Just picked up on this thread a bit late. I find it difficult to believe that you would need stronger push rods, no matter how strong the valve springs are. I had a similar problem after I rebuilt my engine and used unleaded fuel for the first time. I bent two pushrods on one occasion and broke a rocker on another. This with standard springs. I believe that the unleaded valve guides need more clearance than standard as they expand more and cause the valves to stick. There was also a rumour at the time (I learned afterwards) that one of the petrol companies had been playing around with the fuel mix and had got it wrong (the RAC had a lot of damaged valve gear calls). Anyway, I reamed the valve guides to allow more clearance and it's been fine for the last 8 or 9 years.

Got to be cheaper than a new set of 'uprated' push rods.

Jerry

[88V8]

Just picked up on this thread a bit late. I find it difficult to believe that you would need stronger push rods, no matter how strong the valve springs are.

Agree. And the pushrods are acting as a safety valve. If you fit stronger ones without identifying the true cause then something will break.

 

Certainly I would renew the bent rods as once bent they cannot be straightened, but as to the cause either you have coil binding as ntc has hinted, or the rockers are seizing or the valves are siezing. If Richard Crawley were here he'd be clucking about bronze valve guides, I won't say anything about that but if you have valve-stem oil seals I suggest you take them off. Engine not designed for them.

 

Your rockers are standard, aren't they... so you don't have rollers with the wrong pushrods....

 

Ivor

[foster461]

Agree. And the pushrods are acting as a safety valve. If you fit stronger ones without identifying the true cause then something will break.

 

Certainly I would renew the bent rods as once bent they cannot be straightened, but as to the cause either you have coil binding as ntc has hinted, or the rockers are seizing or the valves are siezing. If Richard Crawley were here he'd be clucking about bronze valve guides, I won't say anything about that but if you have valve-stem oil seals I suggest you take them off. Engine not designed for them.

 

Your rockers are standard, aren't they... so you don't have rollers with the wrong pushrods....

 

Ivor

 

When I had my head machining work done last winter there was a line item to ream the new bronze guides to match the new SS valves. I thought that was interesting and have had no issues so far ( I have teflon valve seals also) and this motor has seen 6000+rpm on a few occasions, shortened tubular pushrods, roller rockers.

 

Stan

[Mike C]

David,

I really think you have an assembly problem.A quiet run at low speed shouldn't cause the valve guides to stick if the head was assembled properly.Were the two pushrods from exhaust valves? Two exhaust valves might indicate sticking - but at 2500 rpm on a quiet drive there would have to be something wrong with the head assembly for this to happen.

You are probably aware that there are at least 3 different lengths of standard pushrod used in different versions of the TR 2.5 litre engine.Is there any chance you got 2 long ones from a US spec engine?

But really I suspect your problem was caused by something mundane -like the pushrods not being properly seated in the cam followers when the tappets were set.

 

Regards,

[david johnson]

Thanks for the views and advice. The problem was that two of the rockers had almost siezed on the shaft. This was due to lack of oil because the oil way under the rocker pedestal was blocked with old black oily gunk. The block had been chemically cleaned, and the altered head when it returned looked perfect. This muck must have been somewhere in the head oilways. We cleaned out the blockage, will rebuild the rocker gear, and have fitted the rocker oil feed. No apparent other damage, but will have to check cam for lift. Thanks David Johnson