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Bent Push Rod – 1970 T100S #141979 05/25/08 8:36 pm
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Matthew Manton Offline OP
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Hi Guys,

Just got my good wife to come and rescue me in the van after my bike started to lose power on a trip at the weekend.

When I got home this afternoon and started to dismantle the rocker boxes I found my problem was this bent right side inlet push rod shown below.
[Linked Image]

Over the winter I did some work on my engine and installed new push rods, tappets and all new gaskets. Put grease in the tappet cups to make sure the pushrods were seated correctly. I was well pleased with myself because I got rid of those pesky leaks around the push rod tubes.

I wonder if I could get some guidance on why this push rod has taken on its present ugly shape.

After getting the bike on the road I did the following:

30 Miles: Re-torqued the head to 25 LBS and adjusted valve clearances.
130 Miles: Re-torqued the head to 25 LBS and adjusted valve clearances
330 Miles: Re-torqued the head to 25 LBS and adjusted valve clearances
400 Miles: Checked and adjusted valve clearances

The valve clearances were set to Inlet: 0.004” and Exhaust: 0.006”. These clearances are 0.002” plus over the specified clearances. The bike went and sounded great.

I did notice at the 330 mile check up that the offending inlet right side valve clearance was way off. You could of got a double decker bus through the gap – should have figured something was amiss then. At the 400 mile check up that offending clearance was a little on the loose side, but the adjuster lock nut was good and tight.

So on Monday morning I will get a couple of new push rods and a pair of tappets, as one of the tappets was damaged in this little skirmish within the pushrod tubes.

Any thoughts on what went wrong here?


Matthew
1970 T100S
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Re: Bent Push Rod – 1970 T100S #141980 05/25/08 8:55 pm
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Blapper Offline
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Hi Matthew,

My thoughts are that it may be a pattern part which is not the right grade of ali, or most likely that it was slightly bent from new and the bend got slowly worse but that failure occurred rapidly as the bend got worse.

redwine

Re: Bent Push Rod – 1970 T100S #141981 05/25/08 8:58 pm
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dale karger Offline
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judging how the one end of the pushrod has a lip on it...something on your top end bound up or God forbid the piston smacked the valve pushing it backwards at the time the pushrod was trying to open it. Or you got a defective rod... highly unlikely but not impossible. as for what stuck... valve stuck closed? rocker bound hard due to?? it should be pretty each to find the culprit. finding out what will probably tell you why as well.


76 T140V
79 Honda CB 650
79 Yamaha 175 Enduro
68 Chevy Impala Convert
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Re: Bent Push Rod – 1970 T100S #141982 05/25/08 10:14 pm
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dave jones Offline
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I read somewhere that worn camshafts cause pushrods to come out of the tappets. I don't know if it is true but they are easy enough to change on a 500.
dave

Re: Bent Push Rod – 1970 T100S #141983 05/25/08 11:21 pm
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John RGS Offline
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This pushrod has not seated on the rocker ball written all over it. Check the inside of the rocker box in the corresponding location for the matching gouges. It's difficult to see inside the boxes on a T100 when your trying to seat them properly.


,_o
_ -\_<,
(*)/'(*)

NOPGS #2
Re: Bent Push Rod – 1970 T100S #141984 05/25/08 11:59 pm
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Matthew Manton Offline OP
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Thanks for all your help guys.

What I did notice when I took the inlet rocker box off was that the pushrod steel sleeve at the top had come off, just sitting in the bottom of the head.

The other inlet pushrod also had a loose steel sleeve as well. These are brand new pushrods that I just purchased from British Cycle Supply.


Matthew
1970 T100S
Re: Bent Push Rod – 1970 T100S #141985 05/26/08 3:19 am
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RF Whatley Offline
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Quote
Originally posted by Matthew Manton:
When I got home and started to dismantle the rocker boxes I found my problem was this bent right side inlet push rod shown below.
[Linked Image]
Matt -

Very sorry to hear of your issue, especially after you took such care in assy and run-in. However, you would be wiser to say that you found the symptom rather than the "problem".

The actual problem could be...
• Poor quality push rods
• Piston striking valve, cause by
.....Slack in the rods
.....Cam timing
.....Wrong pistons
• Tight fit tappets in tappet blocks
• Over-revving
• Etc

Good luck. :bigt:


Don't hide 'em, Ride 'em !!

RF Whatley
Cornelia, GA
Re: Bent Push Rod – 1970 T100S #141986 05/26/08 12:04 pm
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Tiger Offline
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Quote
Originally posted by Blapper:
Hi Matthew,

My thoughts are that it may be a pattern part which is not the right grade of ali, or most likely that it was slightly bent from new and the bend got slowly worse but that failure occurred rapidly as the bend got worse.

redwine


1969 TR6R
7.62 x 51 is not a maths puzzle.
Re: Bent Push Rod – 1970 T100S #141987 05/26/08 1:16 pm
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John Healy Offline
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Quote
Originally posted by Tiger:
Quote
Originally posted by Blapper:
[b] Hi Matthew,

My thoughts are that it may be a pattern part which is not the right grade of ali, or most likely that it was slightly bent from new and the bend got slowly worse but that failure occurred rapidly as the bend got worse.

redwine
[/b]
Doubtfull!


Re: Bent Push Rod – 1970 T100S #141988 05/26/08 2:30 pm
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2
2twins Offline
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My first guess is a sticky valve. Did you do any work on the cylinder head for your rebuild?


Woody 2Twins
Re: Bent Push Rod – 1970 T100S #141989 05/26/08 2:59 pm
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Matthew Manton Offline OP
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When I initially rebuilt the bike, and I have done 9,000 miles on it so far, I renewed all the valves, springs, and valve guides.

I haven’t got to it yet but later today I will dismantle the offending valve and see what the valve stem fit is like in the valve guide.


Matthew
1970 T100S
Re: Bent Push Rod – 1970 T100S #141990 05/26/08 5:37 pm
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GrandPaul Online Content
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1. Why .002 over on the lash settings? that's a lot of slop waiting to liberate metallic molecules.

2. Have you carefully examined your valve guides and seats? I'll bet they aren't hunky dorey.

3. That photo shows a puchrod that is a LOT more BROKEN than it is BENT.

Chasing quality / construction issues is a different bunny trail than the mechanical cause & effect scenario that seems evident in the photo. (to me, at least)


GrandPaul (does not use emoticons)
Author of the book "Old Bikes"
Too many bikes to list, mostly Triumph & Norton, some BSA & European
"The Iron in your blood should be Vintage"
Re: Bent Push Rod – 1970 T100S #141991 05/26/08 6:10 pm
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dale karger Offline
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I grew up in the parts business and have seen my share of inferior and sub standard parts. But I have also seen parts being blamed first for the problem. It happens, there are defects but more often than not IF the part fails all on its own it is usually a case of the wrong part being installed. The original tolerances needed are no longer in place and the new ( incorrect part ) is too tight, too loose, out of alignment, etc....and that difference may be too slight to notice! If the part was bought from a reputible dealer and is correct the chances are fairly slim it is the part is solely the blame. NOT impossible but I would look to other causes. installer error ( we all have brain farts at one time or another or the part is a bugger to install) , something binds up, or something comes loose/breaks and subsequently mis-aligned. You have the effect the causes in this case are few and should be easy to find. Tear it down and tell us what you find.


76 T140V
79 Honda CB 650
79 Yamaha 175 Enduro
68 Chevy Impala Convert
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Re: Bent Push Rod – 1970 T100S #141992 05/26/08 6:12 pm
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don1 Offline
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Judging by the lip around the pushrod there is a possibility that the tappet cup was not seated properly on the pushrod.Over the miles it has hammered the two parts together increasing the clearance so that the pushrod came off the tappet causing the resultant damage. Another possibility is that the hardened foot came off the cam follower and the cam follower dropped with the same result.Although not very common I have seen both faults happen in the past. Don TT600.


don1
Re: Bent Push Rod – 1970 T100S #141993 05/29/08 12:43 am
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Matthew Manton Offline OP
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Hi Guys,

I had a lock at my tale of woe today.

All the push rod steel caps were loose, and there was damage on the top of the tappet where the push rod was doing the Macarena on it. But no other signs of trauma.

I dismantled the offending inlet valve and the valve was a good sliding fit in the valve guides. Tappets were also good sliding fits.

If previously on my rebuild I did not quite get the push rod onto the rocker ball would the bike have purred along for 400 miles sounding just fine, no rattle and clanging?

When installing the pushrods I filled the tappet cups with grease and could feel the sucking of the grease when they were home.

Ordered new parts and any words of wisdom for my next rebuild would be appreciated.


Matthew
1970 T100S
Re: Bent Push Rod – 1970 T100S #141994 05/29/08 3:32 am
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GrandPaul Online Content
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I don't think mis-installed parts would run 400 miles.

I DO think an intermittent sticky cam follower or rocker/shaft could certainly cause it.


GrandPaul (does not use emoticons)
Author of the book "Old Bikes"
Too many bikes to list, mostly Triumph & Norton, some BSA & European
"The Iron in your blood should be Vintage"
Re: Bent Push Rod – 1970 T100S #141995 05/29/08 6:53 am
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Blapper Offline
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I don't think you have any chance of it being a badly seated pushrod, they would jump off a lot sooner than 400+ miles. Any witness marks to that effect?

So tell us more about the damage to the tappets (I take it you do mean cam followers-yes?)? Also, what work did you do over the winter?

Blapper redwine

Re: Bent Push Rod – 1970 T100S #141996 05/29/08 10:56 am
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gs750 Offline
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Grand Paul

Quote
I don't think mis-installed parts would run 400 miles.

I DO think an intermittent sticky cam follower or rocker/shaft could certainly cause it.
Also, does the 'sliding fit' valve stem rotate completely freely in the guide along its full length?.


1971 Triumph T100C
1974 Honda XL350
1982 Suzuki GS750T
2000 Honda VFR800FI
Re: Bent Push Rod – 1970 T100S #141997 05/29/08 11:21 am
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dave jones Offline
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What did the cam lobes look like? I definitely read once that if they have worn they can make the pushrods jump ship.

Re: Bent Push Rod – 1970 T100S #141998 05/29/08 11:48 am
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John RGS Offline
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When you put it back together use a dentist mirror to make sure the push rods are seated properly on the rockers.


,_o
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(*)/'(*)

NOPGS #2
Re: Bent Push Rod – 1970 T100S #141999 05/29/08 12:08 pm
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Tiger Offline
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I cannot see how a pushrod bent like that could be contained within the engine ?
Maybe you set valve clearances referencing inlet/exhaust on the same cylinder rather than exh/exh in/in on opposing cylinders ?
It is possible that the above combined with incorrect crankshaft position could have resulted in both ends of the pushrod catching on the tips of the cam follower and rocker ball ends ?


1969 TR6R
7.62 x 51 is not a maths puzzle.
Re: Bent Push Rod – 1970 T100S #142000 05/29/08 2:50 pm
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Matthew Manton Offline OP
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Hi Guys,


I feel confidant that I did install the pushrods correctly.

The damage to the cam followers is shown below, two chips on the cup end. No other witness marks anywhere.
[Linked Image]

The 'sliding fit' valve stem does rotate completely freely in the guide along its full length.

Over the winter I did the following:
Installed new push rods
Cam followers
Mushroom head tappet adjusters
All new gaskets

Tigers Comment:
“Maybe you set valve clearances referencing inlet/exhaust on the same cylinder rather than exh/exh in/in on opposing cylinders ?
It is possible that the above combined with incorrect crankshaft position could have resulted in both ends of the pushrod catching on the tips of the cam follower and rocker ball ends ?”

Set the clearances as per the manual, except I added .002” to the clearances Inlet 0.004” and Exhaust 0.006”. When one tappet adjuster was down one side I set the clearance for the other side.


Matthew
1970 T100S
Re: Bent Push Rod – 1970 T100S #142001 05/29/08 3:58 pm
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Blapper Offline
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So Matthew, you didn't do any blasting or anything which may have resulted in a lump of hard crud in a rocker or valve stem?

Did you roll the pushrods on a flat surface to check straightness before fitting?

Just trying to stimulate some thought.

Blapper redwine

Re: Bent Push Rod – 1970 T100S #142002 05/29/08 4:48 pm
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HARRYKUK Offline
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This is also symptomatic for a broken inner valve spring, do'nt ask how I know! confused eek mad shocked

Best of luck.. HarryKUK beerchug

Re: Bent Push Rod – 1970 T100S #142003 05/29/08 6:27 pm
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aceaceca Offline
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Better check for coil bind while at it.

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