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#328157 - 08/14/10 3:25 pm Valve hits piston  
Joined: Jun 2007
Posts: 75
Troels Mygind Offline
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Troels Mygind  Offline
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Posts: 75
Denmark
Im trying to get my preunit ready to get on the road for The Raceday at Mosten MC in week 35, but keep hitting "the wall of problems"
Im building a 650(t11O) crankcases with 750 Morgo and alu head, but now the valves hits the pistons. I now have 3 headgaskets (1mm/0,04inch each) and there is now only ½ a turn on the adjuster until the inletvalve hits.
Stan Shentons "Triumph Tuning" says there must be one hole turn(1mm/0.04inch)as a minimum.
I guess the head is skimmed by previos owner, heigth between surface and bolthead is 71mm.
What the .... can I do to get on with the project?
I have acces to lasercutting and can get a 2mm plate cut, so I can put copper/steel/copper between cylinder and head?


1954 Speedtwin 5T Pre-Unit
Greetings from Denmark
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#328160 - 08/14/10 3:40 pm Re: Valve hits piston [Re: Troels Mygind]  
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Ducknaldo Offline
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Ducknaldo  Offline
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Posts: 468
Denmark
Hej Troels

Nice to hear that you are almost ready to ride:)
Several head gaskets really isn´t a great way to go, imo.
You can get 0.080 head gasket for morgo and routt kits at tricore and you can get a steel plate for the base, which I think is also 0.080, this should give you almost the clearance you need.
I seem to recall that you are using some kind of racing cams.
If you have access to laser cutting equipment, I would get one of the thick head gaskets and cut a base steel plate in the correct thickness to achieve the clearance you need.
Too many head gaskets will give you some other headaches regarding prt o-rings and blow-by.

Hvis du vil have det på dansk skriver du bare;)


*******************
Run `em...
*******************
1969 T120
#328161 - 08/14/10 3:49 pm Re: Valve hits piston [Re: Ducknaldo]  
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Troels Mygind Offline
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Troels Mygind  Offline
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Denmark
Hej, rart med danskere herinde også.
(Nice with more danes:) )

When you say base steelplate do you then mean a plate to place under the barrel?


1954 Speedtwin 5T Pre-Unit
Greetings from Denmark
#328165 - 08/14/10 4:20 pm Re: Valve hits piston [Re: triton thrasher]  
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Troels Mygind Offline
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Troels Mygind  Offline
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Denmark
Im using E3134 in and outlet cams, will check the timing after dinner and get back to you then, proberbly about 19:00 to 19:30.


1954 Speedtwin 5T Pre-Unit
Greetings from Denmark
#328173 - 08/14/10 5:41 pm Re: Valve hits piston [Re: Troels Mygind]  
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Posts: 3,549
Pete R - R.I.P. Offline
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Vic. Australia
At 0.040" clearance,there's not much to spare and the valve will most likely contact the piston when the engine is hot.It won't do much harm if its just an intake valve.
You should have 0.060" clearance on the intake valve.
You must have 0.080" clearance between the exhaust valve and piston.

With 3134 cams you should have 0.140"-0.145" valve lift at TDC.If you're out by one tooth on the cam timing,the TDC lift will change by about 0.055".

Use one head gasket if it gives you 0.045" or more squish between the pistons and head.
If you like the cam timing you have,increase the depth of valve pockets in the pistons.
The easy way for now would be to open the intake valve later,to gain clearance.
Check the exhaust too.At least if you advance the exhaust cam,there's not much power loss.It may even run better at low speeds.

#328180 - 08/14/10 6:13 pm Re: Valve hits piston [Re: Pete R - R.I.P.]  
Joined: Mar 2005
Posts: 9,965
John Healy Online content
John Healy  Online Content



Joined: Mar 2005
Posts: 9,965
Boston, Massachusetts
A stock head is a little less than 71mm thick so I don't think the head is the issue.

You all are assuming that it is the depth and not the radius of the valve pocket in the piston. If it is the radius of the valve pocket in the piston you will be loosing an awful lot of needed compression raising the cylinder head before the edge of the valve stops hitting it. IMHO you are approaching this the wrong way.

I am not with Pete on the valve clearance issues. I routinely ran .040: intake and .060" exhaust even on the 5T and T100's we ran for years using the early squish head. Both of those motor routinely saw more than 9,000 rpm and I have never had a valve hit a piston or hooked the intake and exhaust valve on overlap. Our 750's were routinely set-up this way.

Way to many questions:
New valve seats?
Oversize valves?
Valves with very heavy margins?
Dimension, depth and radius of piston's valve pockets?

Not only will the valve hit the piston due to changes with performance cams, but almost as often due to the depth and radius of the piston's valve pocket. Often one has to change the geometry of the valve or depth of the valve seat because there is not enough material to remove from the piston valve pocket to get the required clearance. It varies with the piston, but about as thin as you want to get the piston in the area under the valve pocket is .125" so you have limited amount of metal that can removed from the piston to get the required clearance. While increasing the radius of the valve pocket is seldom an issue with these pistons, if you are working on a 500 you can easily cut right into the back of the top ring groove. You will often see performance pistons for the 500 where they have lowered the top compression ring groove to accommodate the valve pocket.

But the E3134 cam is very, very mild indeed and is not a cam where I would think it would cause you any problems. I am leaning toward the valve itself or the valve seat. Most pistons have a deep enough pocket for this cam and a stock diameter/margin thickness valve. Most machinists don't put a new valve seat in the head properly. Change things and the chase for clearance is on!
Just some thoughts.

A dollop of modeling clay, a single AMAL throttle spring (to replace the valve springs) and a bit of careful turning should show you your problem.

Last edited by John Healy; 08/14/10 6:22 pm.

#328184 - 08/14/10 6:41 pm Re: Valve hits piston [Re: John Healy]  
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t120mike Offline
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t120mike  Offline
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hampshire, england
John,

I am OH!SO interested in this topic as I will be facing it shortly. I have Triumph 650 9-stud heads with stock pistons but almost everything else, i.e. valves, seats, guides, cams and followers are special. Cam timing is to be set by degree wheel, not by markings on the cam and idler pinions. So a good method of finding the piston to valve clearance will be essential. Your description "A dollop of modeling clay, a single AMAL throttle spring (to replace the valve springs) and a bit of careful turning should show you your problem." is tantalisingly brief. Is there a link somewhere to the "valve/piston clearances for dummies" version?
Also, IYO, if one cylinder passes the test, is it safe to assume that the other(s) will also be ok or is there sufficient anecdotal evidence to suggest otherwise?


mike
Member #: 147
1960 T120 Bonneville
1999 H*%^a VFR 800 FI
V4 Triton Project (still keeping me sane (Ha-Ha!))
#328195 - 08/14/10 8:01 pm Re: Valve hits piston [Re: t120mike]  
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Posts: 75
Troels Mygind Offline
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Posts: 75
Denmark
Set the pistons at TDC and use the valve adjuster screw as micrometer is a fairly simple and precise way for finding the gap between piston and valve. You simply turn the screw until the valve touch the piston, one turn on the screw is 0,040 inch or 1mm.

Anyway my camtiming was WAYOUT, I must have read the timingdisc wrong (or had to many pints while working...).
The inlet camwheel came pretty easy out, but I have not been so lucky with the exhaustwheel yet. (My dealer didn't have the extractor when I wanted to by it, sucks a little.)
Now I'll give it a shot again, hope to get it right before I'm going to bed so I won't have to think more about it smile .


1954 Speedtwin 5T Pre-Unit
Greetings from Denmark
#328210 - 08/14/10 9:54 pm Re: Valve hits piston [Re: Troels Mygind]  
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Troels Mygind Offline
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Troels Mygind  Offline
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Posts: 75
Denmark
Got the wheel of, made a extractor by welding a nut, two angular bars and a steelring together smile
Now I'm timing once again and hope my problems are solved (at least regarding this challenge:) )


1954 Speedtwin 5T Pre-Unit
Greetings from Denmark
#328214 - 08/14/10 10:55 pm Re: Valve hits piston [Re: t120mike]  
Joined: Jul 2009
Posts: 3,549
Pete R - R.I.P. Offline
In Remembrance
Pete R - R.I.P.  Offline
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Joined: Jul 2009
Posts: 3,549
Vic. Australia
Originally Posted By: t120mike

stock pistons but almost everything else, i.e. valves, seats, guides, cams and followers are special. Cam timing is to be set by degree wheel, not by markings on the cam and idler pinions.

Also, IYO, if one cylinder passes the test, is it safe to assume that the other(s) will also be ok or is there sufficient anecdotal evidence to suggest otherwise?

If one cylinder passes easily,you'd be pretty safe unless there's some noticable differences in valve seat height.
If your cams have a lot more duration,and lift at TDC,you won't be that lucky with 9:1 Hepolite pistons.Most likely no cylinders will pass.
Strips of clay on the piston will tell you if the valve pocket is the correct radius,and positioned centrally to the valve.The radius should be 1/32" bigger than the valve radius (1/16" bigger diameter).
Its not a bad idea to measure how far you can open a valve before it hits the piston at TDC (no need for any springs at that stage).This will give you an idea of how much valve lift you can use at TDC.I reckon some cam manufacturers don't use much more overlap in their timing spec's,so they can sell cams to people who won't deepen valve pockets (lost performance).

You can deepen the valve pockets while the pistons are in the cylinders,if you weld some tool-bits (old drill-bits etc.)onto an old valve and sharpen them to suit.
Its then an easy matter to fit the head with light springs and check the clearance as you go.

Doing valve timing with a degree wheel,I never take much notice of the timings at 0.020" lift.Check it at 0.100" lift and you'll get a better picture of the true cam centreline.

#328251 - 08/15/10 6:20 am Re: Valve hits piston [Re: triton thrasher]  
Joined: Aug 2001
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triton thrasher Online content
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triton thrasher  Online Content
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scotland
Originally Posted By: triton thrasher
Sounds like you need to advance the inlet cam.


I mean retard, don't I!


Amateur Loctite enthusiast.
#328264 - 08/15/10 12:35 pm Re: Valve hits piston [Re: triton thrasher]  
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Posts: 75
Troels Mygind Offline
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Troels Mygind  Offline
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Posts: 75
Denmark
OK, here we go again.
Have done the timing again and now a tour around starting at TDC with both valves closed and rotating cranckshaft clockwise at timingside:
EX opens 55° before BDC
IN opens 35° before TDC
EX close 40° after TDC
IN close 55° after BDC
(E3134 IN and EX cams)
Does this sound correct for the experts?


1954 Speedtwin 5T Pre-Unit
Greetings from Denmark
#328273 - 08/15/10 1:20 pm Re: Valve hits piston [Re: Troels Mygind]  
Joined: Mar 2005
Posts: 9,965
John Healy Online content
John Healy  Online Content



Joined: Mar 2005
Posts: 9,965
Boston, Massachusetts
http://www.postdiluvian.org/~mason/moto/cam-timing.html


#328342 - 08/15/10 11:13 pm Re: Valve hits piston [Re: Troels Mygind]  
Joined: Jul 2009
Posts: 3,549
Pete R - R.I.P. Offline
In Remembrance
Pete R - R.I.P.  Offline
In Remembrance

Joined: Jul 2009
Posts: 3,549
Vic. Australia
Originally Posted By: Troels Mygind
OK, here we go again.

EX opens 55° before BDC
IN opens 35° before TDC
EX close 40° after TDC
IN close 55° after BDC
(E3134 IN and EX cams)
Does this sound correct for the experts?


That sounds normal for 0.020" lift at the follower or pushrod.Check it again at 0.100" lift and see if that agrees.
0.020" figures are not always accurate within 5 degrees.

Then check your valve-to piston clearance;you should be happy with it.

#328346 - 08/15/10 11:49 pm Re: Valve hits piston [Re: John Healy]  
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Posts: 918
t120mike Offline
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t120mike  Offline
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hampshire, england
John,

Many thanks for that URL.

I guess that the reason for using AMAL carb springs when measuring piston-to-valve clearances is that it is easier to rotate the crank in a smooth, controlled manner without the cams, and therefore the crank, being pushed about by strong valve springs!? Would it work just as well using only the small inner valve spring rather than carb springs?

The more I think this through, the less daunting it becomes. I guess that if I put weak springs on one side and leave out the push rods on the other side I will get a result. Also, there would be no need to fit PRTs, for this test, thus saving on "O"-rings and frayed tempers.

I have now got three methods of measuring the clearance from this marvellous Board (thanks guys):
1. Plasticene on the piston crown.
2. Using the valve clearance adjuster to close the gap; one full turn = 0.0385" (26 tpi).
3. Use a dial guage on the valve spring collar and close the gap using a prying device.

I guess the plasticene method is the one that will best show WHERE the potential conflict will be and whether the answer is recessing the valves or enlaging the machined "land" on the piston crown.

I have also learned that the check should be done at 15, 10 and 5 degrees BTDC (in) and 5, 10 and 15 degrees ATDC (ex).

Milky Bars all round! beerchug

PS. I got assembly lube and copper grease but I still sneak into derelict buildings (aka my shed) and use Loctite. Apparently the medical term for my condition is "threadlock-abuse". They now have celebrity rehab clinics, I hear!


mike
Member #: 147
1960 T120 Bonneville
1999 H*%^a VFR 800 FI
V4 Triton Project (still keeping me sane (Ha-Ha!))

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