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Post by simonlc on Apr 17, 2022 19:02:47 GMT 1
Keeps blowing right hand side head gasket. Go for a run and couple miles goes onto one cylinder and then starts boiling and pressurising the cooling system. Fitted 2 x head gaskets now and still same and blows in the same place. Also slight drip from head gasket when stood on the same blowing side. I am thinking warped cylinder head.
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Post by mak595 on Apr 17, 2022 21:32:39 GMT 1
Cylinder head or barrel heights?
LC or PV?
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Post by 4l04ever on Apr 17, 2022 21:50:47 GMT 1
You may need to get the cylinders skimmed. My engineer can do this for you, as I had a 25mm thick jig plate made specifically for this issue.
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Post by simonlc on Apr 17, 2022 22:04:03 GMT 1
4L0 LC. Is it possible to physically see the different heights with the flat edge of a steel ruler?
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Post by simonlc on Apr 18, 2022 8:49:53 GMT 1
I may of found potential problem. I have noticed that the pistons and head domes have circular ring marks on them where the piston has been kissing the head on TDC. I am thinking compression is too high due to head being over skimmed. Do we have a rough compression test figure to reference off?
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Post by Tobyjugs on Apr 18, 2022 20:48:14 GMT 1
Are you using a head gasket? Measure the squish height.
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Post by simonlc on Apr 19, 2022 8:16:53 GMT 1
Do you measure squish with head gasket bolted in place
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Post by davecroucher57v on Apr 19, 2022 19:56:35 GMT 1
yes.
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Post by steve63 on Apr 20, 2022 13:01:43 GMT 1
If the piston is hitting the head then I would say your squish is close to zero. You say "domes" so it's both pots? If so it's probably a good thing that both are the same. There was/is a school of thought that said the piston should just make contact with the head at max rpm (when the rod stretches it's maximum) just squeezing every last drop of fuel towards the spark plug. I don't suppose you want or require that  Maybe it needed thicker base gaskets? Maybe that's your solution? Sounds like fit thicker gasket then measure your squish. |
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Post by tacky1 on Apr 20, 2022 15:36:45 GMT 1
I had a similar problem with one of my PVs, Kept boiling and blowing gaskets, Measured the squish and it was set up for race gas, sent out the head and they re-cut the dome and squish and zero probs since, I had the squish cut to 1mm
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Post by muttsnuts on Apr 20, 2022 19:47:12 GMT 1
squish value for road use is normally between 1.00mm ansd 1.20mm (head gasket fitted) a stock engin=e with head gasket is going to measure 1.50mm+ as nearly all head gaskets are at least 1.50mm thick, I set mine to 1.20mm when I machine the heads and O ring them, compression pressures should be around 125psi to 130psi, if you get a reading of 140+psi then you have a high compression
sounds like your head needs a closer looking at
Is your bike a 250 (4L1) bottom end and 350 (4L0) barrels fitted as I know of another problem that crops up from time to time
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Post by simonlc on Apr 20, 2022 20:12:13 GMT 1
Yes it’s a 250 4L1 bottom end with 350 barrels fitted. I was wondering weather 250 head fitted that’s different causing the problem. As a pointer there is no tiny lip at all in the combustion dome that is normally found on a standard head. I have currently ordered 2 x head gaskets to try and prove the theory. I was wondering if thicker base gasket fitted and lifting the barrel would effect port timing?
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Post by muttsnuts on Apr 20, 2022 20:22:24 GMT 1
I suspect I know what your problem is, I can fix it, but will need your barrels and head to do it - had a handful of the same problem through over the years, oddly enough, fixed one at the weekend for a chap - unfortunately I am not prepared to divulge what I suspect the issue is, as this one took me a long time to figure out why certain ones do it and others don't
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Post by simonlc on Apr 20, 2022 21:32:40 GMT 1
OK talk to me. I can confirm though that the head has definitely been skimmed as there is no lip in the combustion dome.
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Post by rodney5501 on Sept 13, 2023 18:30:16 GMT 1
Is a 250 head different to a 350 thanks
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Post by rodney5501 on Sept 13, 2023 18:30:28 GMT 1
Is a 250 head different to a 350 thanks
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Post by stusco on Sept 13, 2023 19:19:38 GMT 1
Part number is the same at fowlers
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Post by muttsnuts on Sept 13, 2023 20:10:05 GMT 1
Is a 250 head different to a 350 thanks yes they are different, combustion dome/squish width is 55.5mm on a 250LC and 65.5mm on a 350LC, there are other differences as well |
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Post by Gitram on Sept 13, 2023 21:20:58 GMT 1
i'm not sure if i understand this, are you using a std 250 head on 350 barrels?
marti
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Post by arrow on Sept 14, 2023 0:29:11 GMT 1
Part number is the same at fowlers Just to avoid any confusion, no they aren't. |
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Post by stusco on Sept 14, 2023 9:25:40 GMT 1
Sorry never noticed the 4l1/4l0 at the start
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Post by simonlc on Apr 1, 2024 22:16:19 GMT 1
I had exactly the same thing as you and turned out to be a 250 head fitted to 350 barrels. The heads are different and t
With a 250 head fitted I won’t last more than 10 mls
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