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[adamscarborough]

Bullet Whisperer,I thought about retarding the inlet cam but I seemed to have to move it a long way, (3 teeth I think), before it would clear. I don't have any experience in this but it seemed too much and I don't know what effect this would have. I think if I tried to reduce the diameter of the inlet valve I'd mess it up.
As you and stinkwheel say, I could make/buy a thin aluminium spacer to put under the barrel, would this have a noticeable effect on power?

stinkwheel, the original copper gasket is around 0.5mm, the one in the gasket kit I have is some weird copper sandwich affair 1.0mm thick, I see H's do a copper one which is 1.0mm.

Revband The head does clamp the 0.5mm gasket properly so I don't think the head has been skimmed before.

My bullet is a 1993, H's didn't recognise the piston, but thought it was European. Is there a piston which is known to be very robust, Bullet proof , especially if I'm having to cut a larger diameter valve cut out?
H's are out of ideas about my problem but have been good at suggestion things to check. The only thing left on the list of checks is to check that the timing pinion key hasn't pushed out, I don't have a puller small enough but don't think it's this.

At the moment I'm thinking:
First, carefully increase the diameter of the valve cut out but not its depth, I think this is a given.
Measure the clearance between the piston and valve, If it only needs a little more, get a 1mm head gasket, if it needs a lot, make/buy a 1mm aluminium barrel spacer.
If I still can't achieve a decent clearance, revert back to the old cams.
I'll use solder as a gauge.

Thanks for your help

[vince]

Hi, unless Im reading it wrong you are using a worn original piston in a new barrel? Why not fit original barrel and cams and rockers and by a process of elimination see which part is causing the problem. As stated earlier to many changes at the same time. Vince.

[Bullet Whisperer]

If the inlet cam has to be retarded by 3 teeth [54 crank degrees !!] for the inlet valve to clear the piston, something is very wrong. Those inlet valves are a nuisance in that they are just too big - I would get rid of it, or reduce its diameter, there will still be plenty of valve to seat contact and those big valves don't contribute any performance gains. Also, because the valve is bigger it will be seated closer to the piston, with less stem sticking out through the guide on the rockerbox side, this can cause trouble with valve springs going coil bound and spring caps hitting the valve guides at [or before] full valve lift. I see from a previous post of yours that the head has been skimmed and that is where I saw the huge inlet valve. How much was taken off the face of the head - too much, I am guessing? Has the barrel been shortened - it is usually safe to take up to 2mm off the height of a barrel and not run into trouble with valves and pistons touching each other. I think that inlet valve is the key to most of your woes, though.

[Revband]

As Bullet Whisperer says the bigger valve is probably your main culprit?, If you really must use it you may need to have the seat cut a bit deeper to give clearance.

But to reiterate the combustion seal on these engines is the barrel spigot (the raised area where the liner sticks up) to head joint, not the head gasket, if the gasket is too thick you end up with a gap between the head and the barrel spigot, this can cause various problems, not least the possibility of the combustion gases leaking to one of the stud holes and burning the alloy away.

[Bullet Whisperer]

Revband, in an ideal world the liner spigot should seal compression via contact with the recess in the cylinder head, but all too often it doesn't. The majority of heads I have removed from Bullet engines [in standard form] have revealed thick bands of carbon on top of the liner spigot and many blown head gaskets have been found to leak down one or more of the barrel stud holes. Indeed, I have just tuned a 350 where I have done away with the head gasket altogether and lapped the underside of the head into the face of the barrel spigot to hold compression, as well as shortening the barrel by 1.5 mm in this case and the slim stem valves are still well clear of the very lumpy piston. Getting the pushrod tunnels to hold oil has been a battle, though, as the tunnels in the head are so out of step with those in the new alloy barrel, there is barely any overlap of the metal faces at the front pushrod tunnel and it has been a right pain trying to seal it. I may even have to get some alloy weld added to the outer edge of the exhaust pushrod tunnel on the head and blend it into the original gasket face to achieve better sealing potential. Regards, Paul.

[adamscarborough]

I'm told the head has been skimmed 0.005in, and as the original 0.5mm head gasket is still being clamped I think this is correct.

The main issue is that the larger inlet valve diameter misses the cut out in the piston. No matter what combination of new and old parts I use the big valve still hits the piston because of this. The valve seat has already been enlarged to accept the new valve so does sit lower. According to H's even without cutting the valve seat and the valve sitting proud there should be enough clearance.

Maybe the big valve always misses the cut out, but in a most engines there is a greater distance between valve and piston and there is something different/wrong with mine. If you can normally skim the barrel by as much as 2mm without causing an issue this is incredible and suggests there is something different/wrong.

The barrel is the same height as the original. Even with the original cams they clash, however there is an improvement with the original rockers as they are 1mm higher. The exhaust valve is perfectly fine.

I'm now thinking could the crank cases have been machined lower? Has anyone got a picture of the piston at TDC in the barrel, how far up does it normally come, is there normally a mm or two left of the barrel showing?

Could the way forward be to enlarge the valve cut out, fit a small spacer between the crank cases and barrel?
What do I need to reduce the diameter of the valve slightly?
Is there a piston that is bullet proof?

[Adrian]

Quote: "I'm now thinking could the crank cases have been machined lower?"



Possibly, the factory has been known to alter the cylinder to crankcase mouth joint face or deck height, but I gathered that was on Electra-X or UCE models where they decided to machine a bit LESS (0.5mm) off to reduce compression a tad (that'd be a metric tad, which is approximately â…ž of an imperial tad).



There MIGHT be some element of this however, I had Bullet Whisperer carry out his famed ASBO modification on my AVL hybrid motor, with the Electra-X the 2mm off the cylinder base flange and 2mm x 10mm band turned off the piston crown usually hikes the compression from 8.5:1 to about 9.2:1. Exactly the same procedure with my engine however produced a compression ratio measured by B.W. at 10:1, a bit more than needed! Again I can only put this down to inconsistent deck heights, as the crankcases on this engine are a set of modified classic items rather than "proper" Electra-X cases.



Again, the inconsistencies with the Samrat versus OEM rockers seem a bit odd and probably require further investigation. Perhaps a higher rocker ratio on the Samrats is giving extra lift for the exhaust valve?



A.

[Adrian]

Sorry, INLET valve! A.

[vince]

Hi, this could be a factor . I have a 350 iron barrel that is 3mm longer between bottom and top faces. Vince

[adamscarborough]

“Perhaps a higher rocker ratio on the Samrats is giving extra lift for the inlet valve”.
I’m sure this is contributing to the issue as there is a 1mm difference in height between the original and new. There is a greater difference between the old and new exhaust rockers but I don’t knowingly have a problem with the exhaust, possibly because the valve is smaller and still sits within the piston’s valve cut out.
If I ever get to the stage where the engine is back together I’ll check the exhaust valve to head clearance before starting the engine.