smoke
Weekend rider
Posts: 81
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Post by smoke on Sept 9, 2021 10:37:59 GMT 1
Hi, I'm just about ta assemble my 31k PV-engine after a rebore, new bearings, rods and oil seals, and plan to do the squish. My idea is to torque barrels and head without base and head gaskets, to get a starting reference value for the squish. Then calculate backwards, i.e. taking into account thicknesses of the gaskets, before skimming the head. The barrels have the same deck height. Do you think this is a good approach, and if so, any ideas of how high torque to apply?
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Post by tacky1 on Sept 9, 2021 21:58:37 GMT 1
I always measure the squish on all my engines, Always, then have the head machined to suit, I use the gaskets that I am going to use in the final build, Torque them to spec, I measure with a cross of solder, that way you get an even measure..... Haven't had a leak or problem doing it this way in over 20 years......
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Post by pdxjim on Sept 9, 2021 22:04:45 GMT 1
Paul is correct.
Assemble with proper head and base gasket and torque to spec.
Then calculate how much to remove to get the squish band where you want it.
Remember, solder must be touching the bore to be accurate ... careful not to snag the tansfer ports.
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Post by Tobyjugs on Sept 9, 2021 22:12:58 GMT 1
Also make sure you have enough combustion volume with your piston at TDC in your cylinder head. This is more important than the squish height.
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smoke
Weekend rider
Posts: 81
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Post by smoke on Sept 10, 2021 6:59:13 GMT 1
I always measure the squish on all my engines, Always, then have the head machined to suit, I use the gaskets that I am going to use in the final build, Torque them to spec, I measure with a cross of solder, that way you get an even measure..... Haven't had a leak or problem doing it this way in over 20 years...... Thanks a lot! I didn't know I could reuse the gaskets, thought they were compressed when torqued and lost some sealing capacity. And what a great trick to tape the solder to the piston head! Will follow your advice!
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smoke
Weekend rider
Posts: 81
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Post by smoke on Sept 10, 2021 7:00:03 GMT 1
Paul is correct. Assemble with proper head and base gasket and torque to spec. Then calculate how much to remove to get the squish band where you want it. Remember, solder must be touching the bore to be accurate ... careful not to snag the tansfer ports. Thanks! I will be careful.
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smoke
Weekend rider
Posts: 81
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Post by smoke on Sept 10, 2021 7:02:18 GMT 1
Also make sure you have enough combustion volume with your piston at TDC in your cylinder head. This is more important than the squish height. Thanks, will do that. Aiming at around 1.2 millimeter squish.
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Post by tacky1 on Sept 10, 2021 14:24:58 GMT 1
Also make sure you have enough combustion volume with your piston at TDC in your cylinder head. This is more important than the squish height. Thanks, will do that. Aiming at around 1.2 millimeter squish. I usually set my lCs and YPVS at 1mm and its plenty safe, Some go down to .8, I dont think that's necessary for road use...
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Post by Tobyjugs on Sept 10, 2021 16:13:43 GMT 1
1,2 mm is good. This is assuming your engine hasn't got a radicle tune. I could waffle on about lots of things but below is what i have also experianced. I have a 350 engine that makes around 65 hp it was set up with 0.90 mm squish height. Later i swapped the cylinder head for a completely standard cylinder head and gasket. The new squish height was now 2.00 mm and slightly lower geometric compression. The power loss was not noticeble and when measured it was less that 3hp difference. The most noticeable change was the engine was running slightly warmer. Squish is to help prevent detonation to bring the engine closer to the raggedy edge of your tune.
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smoke
Weekend rider
Posts: 81
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Post by smoke on Sept 10, 2021 20:07:53 GMT 1
Thanks, will do that. Aiming at around 1.2 millimeter squish. I usually set my lCs and YPVS at 1mm and its plenty safe, Some go down to .8, I dont think that's necessary for road use... Thanks! I'm not that experienced working with these engines so will try to play it safe;)
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smoke
Weekend rider
Posts: 81
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Post by smoke on Sept 10, 2021 20:10:12 GMT 1
1,2 mm is good. This is assuming your engine hasn't got a radicle tune. I could waffle on about lots of things but below is what i have also experianced. I have a 350 engine that makes around 65 hp it was set up with 0.90 mm squish height. Later i swapped the cylinder head for a completely standard cylinder head and gasket. The new squish height was now 2.00 mm and slightly lower geometric compression. The power loss was not noticeble and when measured it was less that 3hp difference. The most noticeable change was the engine was running slightly warmer. Squish is to help prevent detonation to bring the engine closer to the raggedy edge of your tune. Thanks! Standard tune, but will match transfer ports and polish exhaust port. Exhaust and ignition will also be updated.
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Post by muttsnuts on Sept 15, 2021 21:35:03 GMT 1
one point to note on checking, be sure to use a very soft solder as normal plumbers solder is too hard, I use 1.6mm thick as a squish band bigger than that is a waste of time if you going to be machining the cylinder head
I use "rosin core" solder if that helps
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Post by 4l04ever on Sept 15, 2021 21:49:56 GMT 1
I measure through the plug hole with rosin solder. I make a curve in the a piece about 8" long and feed it in. I measure, as above, at the 4 points and take an average. The advantage over the above is that you can check after the final assembly, as the solder does not stay inside.
Make sure you use the leaded solder as the lead free stuff will also be harder to compress.
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Post by muttsnuts on Sept 15, 2021 21:56:19 GMT 1
I measure at 6 points, but that's just me, but then some of the enignes I build, I need to make sure I've accounted for all the variables as one of them blowing up isn't going to be cheap !
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Post by 4l04ever on Sept 15, 2021 22:04:48 GMT 1
I have notice that there is also a bit of slack in the cylinder to head alignment on standard 4L0 cylinders. The trick I found is to move the head in the direction of the lowest squish measurement, or the cylinder away.
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Post by tacky1 on Sept 15, 2021 23:01:59 GMT 1
I measure through the plug hole with rosin solder. I make a curve in the a piece about 8" long and feed it in. I measure, as above, at the 4 points and take an average. The advantage over the above is that you can check after the final assembly, as the solder does not stay inside. Make sure you use the leaded solder as the lead free stuff will also be harder to compress. The problem with poking a bit of solder into the cylinder is you really need to measure 4 + points at one go, When you poke a single or 2 pieces in, the piston will rock and you'll not get a proper measure because of piston rock....
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Post by 4l04ever on Sept 15, 2021 23:14:02 GMT 1
Maybe a little front to rear, but should be minimal left to right. On the next engine I check, I will compare front and rear separate, then together to see if anything changes.
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Post by marrcel on Sept 16, 2021 7:52:02 GMT 1
I measure through the plug hole with rosin solder. I make a curve in the a piece about 8" long and feed it in. I measure, as above, at the 4 points and take an average. The advantage over the above is that you can check after the final assembly, as the solder does not stay inside. Make sure you use the leaded solder as the lead free stuff will also be harder to compress. The problem with poking a bit of solder into the cylinder is you really need to measure 4 + points at one go, When you poke a single or 2 pieces in, the piston will rock and you'll not get a proper measure because of piston rock.... That is why I only measure on the sides😉
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Post by midlifecrisisrd on Sept 16, 2021 8:27:24 GMT 1
I've double checked with the solder down the hole
If you are careful you can do both sides at once but I'm not looking for a 0.9mm, just checking when either the barrels or head don't look standard
Was a good enough indication when I got 0.6 on an RD400 engine with recut heads
Thicker gasket and I had 1.2 which allowing for some rock was well safe
Steve
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Post by JOHN-DYNOSTAR on Sept 16, 2021 8:58:18 GMT 1
Just as an aside if it rattles on one cylinder when you get it built. it may be your big end that is failing. just add an extra 0.5mm gasket on that side and it should disappear .
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smoke
Weekend rider
Posts: 81
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Post by smoke on Sept 16, 2021 14:31:37 GMT 1
one point to note on checking, be sure to use a very soft solder as normal plumbers solder is too hard, I use 1.6mm thick as a squish band bigger than that is a waste of time if you going to be machining the cylinder head I use "rosin core" solder if that helps Thanks! Yes I will use "rosin core".
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smoke
Weekend rider
Posts: 81
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Post by smoke on Sept 16, 2021 14:34:03 GMT 1
I measure through the plug hole with rosin solder. I make a curve in the a piece about 8" long and feed it in. I measure, as above, at the 4 points and take an average. The advantage over the above is that you can check after the final assembly, as the solder does not stay inside. Make sure you use the leaded solder as the lead free stuff will also be harder to compress. Thanks! I will tape to piston head first and measure, but also measure through plug hole.
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smoke
Weekend rider
Posts: 81
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Post by smoke on Oct 9, 2021 8:29:22 GMT 1
In the "£35 Race tune" article a squish between 20-25 thou is recommended for the LC. Isn't this a little low, or can the LC run a lower squish than the YPVS? Or is it possible with the raised exhaust port?
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Post by stusco on Oct 9, 2021 16:54:24 GMT 1
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Post by Tobyjugs on Oct 9, 2021 20:38:38 GMT 1
This is why I rant on about compression ratios. You can have a small squish height if the compression ratio is good. I would just say Smoke stick to 1.2 mm or get it all done professionally by a reputable tuner. It's all the ingredients added in the correct amounts that make a great cake
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smoke
Weekend rider
Posts: 81
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Post by smoke on Oct 10, 2021 13:52:13 GMT 1
This is why I rant on about compression ratios. You can have a small squish height if the compression ratio is good. I would just say Smoke stick to 1.2 mm or get it all done professionally by a reputable tuner. It's all the ingredients added in the correct amounts that make a great cake Yes, I will play it safe - better safe than sorry;). But I was qurious, as I read this article when it was first published, and at that time I didn't have any references for these engines regarding squish. Since then, I didn't read any post in this forum or elsewhere, recommending such low squish.
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smoke
Weekend rider
Posts: 81
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Post by smoke on Oct 10, 2021 14:07:55 GMT 1
This is why I rant on about compression ratios. You can have a small squish height if the compression ratio is good. I would just say Smoke stick to 1.2 mm or get it all done professionally by a reputable tuner. It's all the ingredients added in the correct amounts that make a great cake Yes, I will play it safe - better safe than sorry;). But I was qurious, as I read this article when it was first published, and at that time I didn't have any references for these engines regarding squish. Since then, I didn't read any post in this forum or elsewhere, recommending such low squish. It would be interesting to hear the experiences of those who made these modifications.
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Post by stusco on Oct 10, 2021 14:25:34 GMT 1
4l04ever on here can make you base gaskets of various thickness to help you set your squish
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Post by Tobyjugs on Oct 10, 2021 14:48:34 GMT 1
Yes, I will play it safe - better safe than sorry;). But I was qurious, as I read this article when it was first published, and at that time I didn't have any references for these engines regarding squish. Since then, I didn't read any post in this forum or elsewhere, recommending such low squish. It would be interesting to hear the experiences of those who made these modifications. I have seen some nice internet links to tuning books etc. These are good to read to get a general all round idea of how an engine works with explanations about squish, combustion volume, exhaust lengths etc.
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Post by JOHN-DYNOSTAR on Oct 11, 2021 16:10:52 GMT 1
now here is a scary one. please make sure you fully understand what squish actually is. I had a discussion with a guy last week about squish clearance and it been critical on a certain type of engine 0.90 been a sort of optimum for performance for example. the last I heard was he was machining the heads . the piston was hitting the head before it achieved the correct squish. I am concerned about the above statement.
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