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Post by Bozzy on Jul 15, 2024 14:23:00 GMT 1
As above, you can only decide whether to fit them or not, if there is sufficient clearance for that piston / ring / bore combination. That has not been the case for the last few RIK rings, Mitaka pistons and rebore (PJs) that I've had. If it's too tight and you jam them in there, you'll be forking out again. Checking the rings etc it felt like without the expander that bottom ring would have little impact (being thinner) and recessed back into the groove. The top ring piston recess is the same depth as the bottom ring but the top ring itself is wider making it approx same as second ring with expander. It was a snug fit but I assumed that's the way its designed to push out the ring slightly and take out that bit of piston play I had. turning the motor over all appeared fine. Probably something else I may have done wrong.... add to the list with tight PV and top limit crank, putting 3 bond onto base gasket and not tightening nuts correctly......... :-( |
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neil
Thrash Merchant
my 125
Posts: 386
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Post by neil on Jul 15, 2024 23:29:26 GMT 1
I do remember my 125 had parts of the expander ring missing on a strip down. Must have gone out the exhaust port luckily. It was revved to 10k regularly and had some piston slap!
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Post by urbantangleweed on Jul 16, 2024 6:33:06 GMT 1
Probably something else I may have done wrong.... add to the list with tight PV and top limit crank, putting 3 bond onto base gasket and not tightening nuts correctly......... :-( I find spray Hylomar perfect for paper type gaskets, others use nothing and some prefer to lightly grease the gaskets. Threebond is ideal for sealing metal to metal mating surfaces such as the crankcase halves but is a bit thick and gloopy for base gaskets. It will also "squidge" out on tightening the barrel nuts and there's quite likely more oozed out into the internal crank space than you might imagine. If you feel you want to re-visit the top end, Rob here (4L04ever) does a Siamese type base gasket which is easier to use on re-assembly than two single ones as you avoid any potential issues with centre overlap which can occur with the singles. It would also give you the chance to strip and check the powervalve assemblies to find out why their operation is tight. I seem to remember you were keen to seal the bushes in with silicone, maybe some of this has got between the valve and bush causing the tightness? If you do decide to go in there again, clean all the goo off and use molybdenum grease, silicone is a bit of a bodge and shouldn't be necessary. Remember also to snug up the barrel nuts finger tight, install the head, torque it down first, then tighten the barrel nuts. |
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Post by Bozzy on Jul 16, 2024 13:12:30 GMT 1
Probably something else I may have done wrong.... add to the list with tight PV and top limit crank, putting 3 bond onto base gasket and not tightening nuts correctly......... :-( I find spray Hylomar perfect for paper type gaskets, others use nothing and some prefer to lightly grease the gaskets. Threebond is ideal for sealing metal to metal mating surfaces such as the crankcase halves but is a bit thick and gloopy for base gaskets. It will also "squidge" out on tightening the barrel nuts and there's quite likely more oozed out into the internal crank space than you might imagine. If you feel you want to re-visit the top end, Rob here (4L04ever) does a Siamese type base gasket which is easier to use on re-assembly than two single ones as you avoid any potential issues with centre overlap which can occur with the singles. It would also give you the chance to strip and check the powervalve assemblies to find out why their operation is tight. I seem to remember you were keen to seal the bushes in with silicone, maybe some of this has got between the valve and bush causing the tightness? If you do decide to go in there again, clean all the goo off and use molybdenum grease, silicone is a bit of a bodge and shouldn't be necessary. Remember also to snug up the barrel nuts finger tight, install the head, torque it down first, then tighten the barrel nuts. Thanks. I never thought of checking the potential base gasket overlap...they are gen Yam gaskets. Assume now its all together no way of checking. do you think the 3 bond might give me an issue or anything internally will blow out when running. Regarding the PV one of the bushes is really tight fit and the operation has always been stiff. in its operation zone fully open to 90deg its fine after get quite stiff. TBH not sure if to rip it apart again now get a new OEM head gasket. When its all currently bolted up feels I might be doing something not needed |
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Post by urbantangleweed on Jul 16, 2024 13:26:21 GMT 1
Just continue on. If the leak test goes OK, you can fit it and see how it is. The engines on these come out in 30 minutes if need be anyway.
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Post by Bozzy on Jul 16, 2024 14:49:22 GMT 1
Hi thanks for the advise. I just spoke to Yam parts and now I am feeling I have used too much 3 bond :-( .. did not realize I should only put a dab/finger smear over the back edge.. mine is squeezing out around all joint so told it may have got onto the side of the port which we don't want. Saying I would sort now
So ordered new base gaskets but told I could leave the head bolted up and raise the barrels put new base gaskets on (said its obviously tricky and not one person job) but saves £65 head gasket cost.
Assume this is ok to do? feel I will be then certain base gasket ok and no crap in the ports plus can fasten don the base nuts in correct sequence (which I note is not in the Yam book for the 31k)
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Post by urbantangleweed on Jul 16, 2024 15:35:06 GMT 1
My advice would be don't try and do both cylinders and the head as a unit, it'll likely end in tears......lots of them.
If you have now decided it should come apart, get a Siamese gasket from Rob, you'll understand why when you fit it.
Oh, and a new head gasket is belt and braces.
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Post by Bozzy on Jul 16, 2024 18:18:31 GMT 1
I thought it would not be too bad lifting the unit off as one. then hold above whilst pistons slid back in.. on my mind is splitting the base gasket (now with 3 bond) evenly and any stress on the head.... is it one of those spend the cash do it right
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Post by urbantangleweed on Jul 16, 2024 18:31:33 GMT 1
I thought it would not be too bad lifting the unit off as one. then hold above whilst pistons slid back in.. on my mind is splitting the base gasket (now with 3 bond) evenly and any stress on the head.... is it one of those spend the cash do it right If you fancy giving it a go, then why not. Let us know how it works out. Spending the cash is likely where you'll wish you'd been, but as they say, "You don't know until you try"  |
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Post by fletche36 on Jul 16, 2024 18:35:49 GMT 1
If you are planning on keeping the bike and if like me you are a compulsive "fiddler" it may be worth you getting the head o ringed and squish corrected , then you can remove as often as you like for no cost with the added bonus your bike will run better and it costs not a lot more than an original head gasket. Just a thought.
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Post by Bozzy on Jul 16, 2024 19:04:21 GMT 1
wise words and knowing my current record with this build I should know better had many regrets... new gasket.
Fletche- Thanks... TBH wish I had done that now. All I want to do is get the thing sorted and on the road at this rate I will miss summer and be asking here what to do with a newly built motor and cant go out for a ride to run in
If I went cool head way (always looked at these) is this dyno / re-jetting?. Before strip down the bike has been on a dyno and jetted so was 100% fueling ok.
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Post by fletche36 on Jul 16, 2024 20:38:34 GMT 1
wise words and knowing my current record with this build I should know better had many regrets... new gasket. Fletche- Thanks... TBH wish I had done that now. All I want to do is get the thing sorted and on the road at this rate I will miss summer and be asking here what to do with a newly built motor and cant go out for a ride to run in If I went cool head way (always looked at these) is this dyno / re-jetting?. Before strip down the bike has been on a dyno and jetted so was 100% fueling ok. i couldnt say about cool heads but when mutts did mine for my 250 it just ran better and picked up smoother and stronger with no jetting changes. i think as std they come with a massive squish which can safely be reduced and allows the motor to be more efficient which seems about right. |
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Post by steve63 on Jul 17, 2024 13:07:32 GMT 1
The pressure from behind the ring pushes it out to create the seal. The rings also seal against either the top or bottom of the groove on the way up/down. The spring tension of the rings against the bore and the miniscule extra from the expander does next to nothing once the engine is running. The faster it goes the more pressure and the tighter the seal, up to a point where the rings start to float and the seal breaks. As the groove wears/gets coated with deposits then you get blow past and those brown marks. If you continue then eventually the blow back get so bad the oil on the bores is burnt off, the piston and cylinder temperature rises and it'll seize. I was told that the expander ring is there to help increase the sealing for starting. A racer or even a general engine builder will always err on the side of increased engine reliability and/or power. If there is the slightest chance the expander will cause a failure or lose 0.5 of a horsepower then they will remove that chance. Much like running without a pump. 1 in 1000 chance or pump failing? Then run on pre-mix. I would question the spec and quality of the material the expanders are made of if not OEM but you I would like to think a reputable manufacturer had done their homework |
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Post by Bozzy on Jul 17, 2024 19:22:35 GMT 1
Well as I am ripping the top end apart again after some stupidity with three bond!
I now have the chance to consider the expander ring again and going to remove them... that was the more general view after much searching and speaking to people plus on here.... and then I went and fitted them!
OEM stuff appears fit other its questionable and been said many times.. its the thinner ring designed for the expander that concerned me and a few asking why omit when designed to fit.
But removing also negates the potential "tight" bores as it does push that ring out and does take clearance which like you say makes sense for starting but running an issue I assume.. plus risk of them breaking up and potentially overlapping
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Post by urbantangleweed on Jul 18, 2024 8:32:46 GMT 1
Well as I am ripping the top end apart again after some stupidity with three bond! I now have the chance to consider the expander ring again and going to remove them... that was the more general view after much searching and speaking to people plus on here.... and then I went and fitted them! OEM stuff appears fit other its questionable and been said many times.. its the thinner ring designed for the expander that concerned me and a few asking why omit when designed to fit. But removing also negates the potential "tight" bores as it does push that ring out and does take clearance which like you say makes sense for starting but running an issue I assume.. plus risk of them breaking up and potentially overlapping IIRC, it was PJME who did your rebores? Have you asked them if they size the bore and/or gap the bottom ring to allow for the expander to be fitted or omitted? It would be useful for not only yourself, but also many here, to know what they do. |
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Post by Bozzy on Jul 18, 2024 8:59:10 GMT 1
Hi Yes I have spoken to them and was told best not to fit them. Dont think any specific reference was made to bore size etc but he had seen issues with them and suggested that they go in the bin
Stripped top end again I had OTT the sealant.... also realized no way I could have removed top end as one unit took some doing single..
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Post by Bozzy on Jul 21, 2024 17:37:06 GMT 1
Well I removed one side expander and sat looking at one with one without the without has loads of side clearance between ring groove the one with expander more like the top ring in that less gapping and side to side movement it’s obvious these bottom rings are made for the expander or they would have put a deeper ring like the banshee Fitting them the pistons and rings are more of a tight fit. Without feels nice and smooth with ok but def tighter fit when lowering the barrels. I wanted to fit them but now thinks if better off with a more free piston fit It’s now stoped me in the rebuild...... www.flickr.com/photos/157306324@N08/53870425277/in/datepostedwww.flickr.com/gp/157306324@N08/z0F767S332 |
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