Sh*t, I forgot something. My engine is overbored 1mm or .040" and I put it back together with an OEM standard sized head gasket. Am I going to run into problems with the lip of the gasket extending into the cylinders by .5mm around the circumference? Someone hold me and tell me it's going to be alright.
Head gasket with overbore
- Thread starter freemonty
- Start date
No, it's not going to be alright. If anything, you want the opposite- a gasket slightly larger than your bore. Some gaskets, like copper gaskets, you can file to size.
jimmer said:
Well let's hope the engineers at Kawasaki in 1976 thought of that for the kz400. I am tired of taking this engine apart.
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Having a head gasket that goes into the bore will cause heat issues and promotes detonation. It's best to have it slightly (.020 - .030) larger than your bore. At least even. Smaller is not a good thing.
Well, I'm not going to hold you but you will probably be alright. Most OEM gaskets are made 1-2mm larger than a stock bore to allow for rebores and the fact that the holes are often slightly out of place.
Find a spare gasket or buy a new one or ask someone to measure the bore on a stock OEM gasket - if that's what you bought. Compare that to the new bore size to be sure
Find a spare gasket or buy a new one or ask someone to measure the bore on a stock OEM gasket - if that's what you bought. Compare that to the new bore size to be sure
Stock gaskets are fine for a factory overbore which usually goes to the 4th overbore or +1mm.
The gaskets typically do not go right up to the cylinder bore wall. 0.5mm wider bore on either side is minimal.
That said, anything can happen and you could have gotten a bad gasket machined incorrectly. So its always best to check.
The gaskets typically do not go right up to the cylinder bore wall. 0.5mm wider bore on either side is minimal.
That said, anything can happen and you could have gotten a bad gasket machined incorrectly. So its always best to check.
Where are you getting that information? Gaskets are made slightly larger to aid in cooling and to prevent a hot edge. A hot edge causes carbon buildup and ultimately detonation.teazer said:
It's an hour at most to pull the head. i don't understand going through the effort of building a motor and not wanting to make sure it's right.
Had a few people check the cylinder diameter on OEM gaskets (the same one I bought) and measurements came back as 65.2mm and 65.5mm. I'm also going to check the old OEM gasket that I pulled off when I get home. Stock bore is 64mm and .040" over is 65mm, so I think I'm going to be alright. I should have between .010" and .020" of clearance based on those measurements.
Ultimately, irk miller is right that I should pull it apart and check it, but I think what some of you others mentioned is correct about Kawasaki making the gasket larger than the biggest overbore size. I checked parts diagrams and they offer overbore pistons and rings from the factory in .020" and .040" over sizes, but they only offer 1 OEM gasket size.
I don't know about only 1hr to pull the head though irk! Gotta reset cam timing, cam chain tension, valve clearance, points gap and timing, head bolt torque....take out the trash, feed the hog, do some homework...
Ultimately, irk miller is right that I should pull it apart and check it, but I think what some of you others mentioned is correct about Kawasaki making the gasket larger than the biggest overbore size. I checked parts diagrams and they offer overbore pistons and rings from the factory in .020" and .040" over sizes, but they only offer 1 OEM gasket size.
I don't know about only 1hr to pull the head though irk! Gotta reset cam timing, cam chain tension, valve clearance, points gap and timing, head bolt torque....take out the trash, feed the hog, do some homework...
irk miller said:
Years of building motors and making/modifying stock gaskets for big bores they were not designed for. Cooling does not really occur in that gap. In fact with a large enough gap, it acts tends to encourage detonation on some bikes. I get the idea that the mixture out that far will not normally burn and so will tend to provide a cooling effect or cushion, but that only applies if it's too small to combust as in a squish band. 1mm-1.5mm of an OEM gasket will tend to detonate if conditions are right (or wrong). GT750 is famous for that and comparison of a pile of head gaskets had some with bores and other holes up to 3mm out of place.
I totally agree that it would be better to pull the head and be sure that it is centered over the bores and he can do that while the dog eats his homework.
I think you misunderstand me. I don't mean it will help cool the engine or head in any noticeable way. What I mean is it keeps the gasket itself cooler on the edge to prevent from getting a hot edge. It's the hot edge that can expand with overheating, and will collect carbon and cause detonation. I've seen gaskets fail prematurely for this very reason. I also totally agree that if it's too far of a gap, it also encourages detonation, also because of carbon buildup. In that situation, there's a dead zone of non-flowing air and unburnt carbon collects. In the end, both situations produce the same effect. I have only been building motorcycles since 2005, but I've been racing air-cooled VWs since the early 80s, and I've built more than a dozen small block and big block V8s. I'm a third generation racer. So, I'm not ignorant to this stuff. That said, I'm glad we both agree it needs to be investigated. I hope I'm wrong that he may have an issue.teazer said:
Pretty sure I said that I hope I am wrong. But yeah, fuck science. Right? These things have nothing to do with it. My grandfather was such an ass to tell me to measure twice and cut once.jcw said:
He's kinda implying he didn't use OEM gaskets.
In that case, you're probably right and he should re-check.
I've had Vesrah gasket kits that contained the wrong thickness head gasket.
They don't really care.
Still, hard to believe you would miss when you placed the head gasket on the cylinder that the gasket overlaps or even comes close to the bore.
Just one of those things...
In that case, you're probably right and he should re-check.
I've had Vesrah gasket kits that contained the wrong thickness head gasket.
They don't really care.
Still, hard to believe you would miss when you placed the head gasket on the cylinder that the gasket overlaps or even comes close to the bore.
Just one of those things...
jcw said:
Maybe that's the confusion with our responses. Here's his first statement to open the thread:
freemonty said:
He said he very much did use a OEM head gasket with a +1 overbore and that the lip extends into the cylinder. By that statement he's not wondering if it does. He knows it does. And he buttoned it up, then realized it might be an issue. At least that's how I've been interpreting the statement.
I don't think that's what the sentence means. I read it to mean that he is asking IF it will overhang and IF SO, is that a problem. He is not saying that it does overhang because he didn't notice as he built it. That's my interpretation. My understanding is that he overlooked checking that and if he had checked, he would have asked earlier. And the reason he didn't check it was because he didn't think about it at the time. Hence the opening comment indicating that he just realized that he had not checked at the time.
Bottom line is that you are right that we read things and answer based on how we interpreted the question and sometimes the question is ambiguous or incomplete.
Bottom line is that you are right that we read things and answer based on how we interpreted the question and sometimes the question is ambiguous or incomplete.
teazer said:
You are correct. It did not occur to me at the time to check whether there was overhang. When I wrote the original post I was not aware that gaskets would be slightly oversized so I assumed I had an overhang that I didn't notice. As it turns out the reason I may not have noticed is because there probably isn't a overhang. I apologize that my lack of clarity led to so much contention!
I will PROBABLY pull it apart and check because I'm out of commission anyway until I resolve my throttle cable issues, but I feel much better about it now. The gasket is centered/located by dowels and so there isn't really any movement. THAT I did notice. And with the measurements I've gotten I should be at even or slightly larger on the cylinder gap.
Thanks all for the input, but let's put 'em away and put this to bed.
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