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Doing a full valve job on a 2007 Vespa GTS 250. Long story on how I got to this point, but the timing belt slipped and the intake valves are bent. I plan on replacing both intake valves. I removed one intake valve and noticed that although the guide still looks very round and the valve seems to fit fairly snug, however it looks thinner on one side(left side of photo). If it were damaged I would assume that it would look more oblong.

Not sure if this is a sign that the valve guide was damaged or if this is normal to see the hole starting out off center. Interestingly enough the other side(top side) also appears to thinner on that same side? Appreciate your thoughts before I invest the time and effort to replace the valves?
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Red Devil SH150i (10,000)
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New head for my Honda cost less than $350. You need special measuring devices to properly inspect the head. My advice is to check with AF1 about the cost of rebuilt/new head.
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I'll betcha that is they came from the factory. Put a little oil on the stems, insert them in the guides, spin them with your fingers. Do you feel any wobbling, getting tight then loose? If fine, put it back together. If you still have suspicions, take all of it to a machine shop and get it checked out.
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^ the hole still appears round not out of shape. ^ Wot he said above
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my recommendation is do not replace guides. even cylinder head shops dont do it the correct way. they choose speed over correct methods. old guides would need to be core drilled. then new guides froze and cylinder head heated before install. shops will simply hammer old guides out and hammer new guides in. you can end up with oil leaking into your cylinder from oil that leaks around outside diameter of valve. because they gall the alloy when guide is hammered in and out.

if guide is not cracked it didnt get damaged from valves bending. if new valve moves freely you are fine as far as guides are concerned.
OP
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Thanks!!
Thanks for all the great feedback.. moving ahead with valve replacements based on your feedback.! Fingers crossed
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2016 Vespa GTS300ie abs/asr/ess Settantesimo '70'
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jerryd wrote:
my recommendation is do not replace guides. even cylinder head shops dont do it the correct way. they choose speed over correct methods. old guides would need to be core drilled. then new guides froze and cylinder head heated before install. shops will simply hammer old guides out and hammer new guides in. you can end up with oil leaking into your cylinder from oil that leaks around outside diameter of valve. because they gall the alloy when guide is hammered in and out.

if guide is not cracked it didnt get damaged from valves bending. if new valve moves freely you are fine as far as guides are concerned.
Over here we heat the head to the manufacturers recommended spec and gently 'tap' the guides out or press them out depending what head it is. They don't need hammering as that will damage an alloy head. Rarely need to drill but it can happen on cast iron heads. Alloy head guide fitments don't normally need to be drilled. The guides just drop out if it's done right. Easy job. Head must be checked for truth afterwards, and in any case the OP's cylinder head must be checked due to the trauma it's suffered. He doesn't want a blown head gasket.

Having said all that, guide replacement is not a common thing these days on engines like ours. Indeed, I've never replaced guides on a GTS cylinder head, but it should be possible to do it ok. I've replaced guides on other bigger bikes though. But, it's often better to get another head, and quicker quite often. In addition, many manufacturers don't recommend replacing the guides as it's too risky on some head designs and some engineering firms are rubbish at doing it.

Looking at the pictures those guides could be suspect but it's very hard to tell from a photo. They could be showing signs of stress from the valve bending incident which is why there is some apparent ovalty. You can best tell if they are measured inline with factory specs. The only issue is if the guides are damaged it could affect valve seat alignment and seating. If rebuilt with those guides and the guides are damaged, the motor will probably run ok initially but over a few thousand miles will start to lose power as the seats in the head start to leak from accelerated wear.
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I recommend replacing the entire head with all the valves, also be checked the surfaces of the cams of the distribution shaft and the roller cage at the top of the connecting rod should.
Clearly the checks must be made with comparative instruments and not visually.
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Unless someone in the US is sitting on NOS 250 heads, they are about 1.5x the cost of a 300 head. And both of them are more than the Malossi head, which would be easy to install and allow the scooter to make about 20% more power.
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Motovista wrote:
Unless someone in the US is sitting on NOS 250 heads, they are about 1.5x the cost of a 300 head. And both of them are more than the Malossi head, which would be easy to install and allow the scooter to make about 20% more power.
Well there you go
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Easy
Install the new valves, and see if they seal. I'd rotate the valves a half turn and check again. If they seal, the guides are fine. Probably wiggle them (without springs, of course) to see if the guides seem tight enough, but if the holes are round, they are probably OK.

If the piston bent the valves, I'd also take a look at the connecting rod to be sure it did not get bent. If the valves get bent enough to jam between the head and the piston, possible to bend the con-rod too.
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