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Post by nakedgoose on Jul 27, 2024 3:28:49 GMT 1
Hi guys,
Finishing up the engine rebuild on my '80 rd350lc, trouble I'm having is with setting my timing,
I'm trying to get the engine to TDC, but it always seems to spring/jump past TDC, I get to about 2.7mm before TDC and then the engine will jump forward past TDC by ~2.5mm's, it seems to do this no matter how fast or slow I turn the engine over, plugs are out and dial gauge is down the left spark plug hole,
This issue originally appeared as a hard spot before TDC where I can't turn the engine past it without either a breaker bar, or a fair bit of momentum with my 1/2" ratchet, this only appeared once the head was torqued down, I've taken the head on and off a few times now to confirm this, the squish is above 1.6mm as my solder was still intact when measuring so I don't think that the pistons are contacting the head either,
The jump feels like its compression related but this is my first engine rebuild so not really sure,
any got some ideas I could try?
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Post by abar121 on Jul 27, 2024 8:14:36 GMT 1
Hmm, something isn't right.
Is the kickstart wrongly engaging?
There should be nothing resisting when turning it over with the plugs out.
Take off the right cover and see what's happening. Strip down further as needed.
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Post by lcmarky on Jul 27, 2024 8:23:07 GMT 1
Odd indeed.
Do you recall the crank rotating freely prior to top end going on?
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Post by lcmarky on Jul 27, 2024 8:26:32 GMT 1
Might be wise to pull the head & barrels to check bore diameters are parallel.
If the bore diameter is tapered towards the top of the stroke sufficiently then that could be a cause perhaps?
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Post by Tobyjugs on Jul 27, 2024 9:14:57 GMT 1
I reckon the piston is hitting the cylinder head.
Loosed the cylinder head and turn the engine over.
First make sure there is no coolant in the engine.
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Post by abar121 on Jul 27, 2024 9:22:08 GMT 1
Ring catching?
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Post by lcmarky on Jul 27, 2024 9:31:05 GMT 1
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Post by badger1 on Jul 27, 2024 9:39:53 GMT 1
Did it turn over ok before you put the barrels on?
Did it turn over ok after you tightened the primary’s?
How did you lock the primary’s ? Sometimes if you’ve used a bit of copper pipe you can get a little bit stuck in the teeth, causing a tight spot.
I always check the movement after every stage of a build just to make sure what I’ve just done is ok.
Hopefully it’s something silly nothing worse than having to strip it down again.
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Post by jon on Jul 27, 2024 9:54:41 GMT 1
I know you said it didn’t happen before you torqued the head down, but could you just not have noticed it?
I thought about primary gears also. Don’t wish to alarm you but if the crank was twisted it could cause a tight spot and then jump.
If it comes to it take the primary gear off and see if it still does it? At the same time a DTI on the crank would rule this out.
Jon
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Post by chrisg on Jul 27, 2024 10:03:34 GMT 1
I reckon the piston is hitting the cylinder head. Loosed the cylinder head and turn the engine over. First make sure there is no coolant in the engine. Maybe hitting the head gasket if its on or near max. rebore. |
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Post by steven on Jul 27, 2024 11:11:38 GMT 1
...as above, piston hitting head gasket ?
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Post by chrisg on Jul 27, 2024 11:41:55 GMT 1
...as above, piston hitting head gasket ? 👍 |
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Post by nakedgoose on Jul 27, 2024 21:33:53 GMT 1
Thanks for all the thoughts, down in NZ hence the delay,
I think I'll start with the kickstart mechanism as that could be done wrong, although the hard spot was present before I installed the kickstarter stuff,
Ill take the head off again and see what I can see, the engine is freshly assembled, hasn't had coolant yet, brand new crank, brand new mitaka piston with fresh rebore on the cylinders the bores are 1.5mm over stock,
My first thought was that the pistons were hitting the head, but after taping 1.6mm rosin core solder in a plus shape on top of both pistons the solder wasn't even touched, was still the same size, which seems like the pistons aren't hitting the head? not to mention my squish seems un-ideal
Piston hitting the head gasket could be a something to investigate, if anything hopefully that is the issue as it should be easy to fix,
The issue only appears once I torque all the head bolts down to the spec
turns over without issues without the barrels on, with the barrels and piston rings on, also with the head bolted down lightly, only once fully torqued to spec, spark plugs in or out doesn't make much difference, its always the left piston at TDC where the hard spot is,
Don't think it'd be the ring catching as surely it would do that without the head on as well?
I'll get to pulling things apart and investigating,
Hopefully I'll have some more info by the end of the day,
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Post by midlifecrisisrd on Jul 27, 2024 21:44:23 GMT 1
At 1.5 over you need to open up the gasket
Easy fix 🙂
Steve
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Post by shaunthe2nd on Jul 27, 2024 21:46:00 GMT 1
Are the 2 barrels same height, if one shorter could be some distortion when head torqued.
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Post by nakedgoose on Jul 27, 2024 22:37:37 GMT 1
At 1.5 over you need to open up the gasket Easy fix 🙂 Steve Didn't know that at all,
How do I go about that doing that?
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Post by steven on Jul 27, 2024 23:09:05 GMT 1
.... long story short, the hole in the head gasket, is not big enough for the over size piston.
i believe some folk dremmel or file the gasket in an attempt to open it up enough, for the bigger piston/piston crown to pass through it.
Steven.
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Post by midlifecrisisrd on Jul 27, 2024 23:31:29 GMT 1
At 1.5 over you need to open up the gasket Easy fix 🙂 Steve Didn't know that at all,
How do I go about that doing that?
As Steven said dremel out the hole till it's about 66mm If you weren't over seas I'd have said sent to Mutts and get it o ringed and recut fir no gasket Steve |
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Post by shaunthe2nd on Jul 27, 2024 23:53:55 GMT 1
At 1.5 over you need to open up the gasket Easy fix 🙂 Steve Steve is that with yam gasket? I usually use athena but dont remember having that problem. |
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Post by nakedgoose on Jul 28, 2024 0:54:30 GMT 1
Didn't know that at all,
How do I go about that doing that?
As Steven said dremel out the hole till it's about 66mm If you weren't over seas I'd have said sent to Mutts and get it o ringed and recut fir no gasket Steve Amusingly the head actually came from mutts as my original had a a bunch of damage,
I'll have a crack at trimming the head gasket asap, hopefully thats all it is.
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Post by midlifecrisisrd on Jul 28, 2024 9:00:25 GMT 1
At 1.5 over you need to open up the gasket Easy fix 🙂 Steve Steve is that with yam gasket? I usually use athena but dont remember having that problem. Yeah, athena us bigger I think Yam only made up to 1mm over Steve |
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Post by Tobyjugs on Jul 28, 2024 13:28:26 GMT 1
Thanks for all the thoughts, down in NZ hence the delay, I think I'll start with the kickstart mechanism as that could be done wrong, although the hard spot was present before I installed the kickstarter stuff, Ill take the head off again and see what I can see, the engine is freshly assembled, hasn't had coolant yet, brand new crank, brand new mitaka piston with fresh rebore on the cylinders the bores are 1.5mm over stock, My first thought was that the pistons were hitting the head, but after taping 1.6mm rosin core solder in a plus shape on top of both pistons the solder wasn't even touched, was still the same size, which seems like the pistons aren't hitting the head? not to mention my squish seems un-ideal Piston hitting the head gasket could be a something to investigate, if anything hopefully that is the issue as it should be easy to fix, The issue only appears once I torque all the head bolts down to the spec turns over without issues without the barrels on, with the barrels and piston rings on, also with the head bolted down lightly, only once fully torqued to spec, spark plugs in or out doesn't make much difference, its always the left piston at TDC where the hard spot is, Don't think it'd be the ring catching as surely it would do that without the head on as well? I'll get to pulling things apart and investigating, Hopefully I'll have some more info by the end of the day, I'm not sure about an Athena head gasket I think it's a little thinner. If all parts are standard your squish band will be more than 2mm high. Another concern is how much force you used to spring the engine over the TDC area. This could potentially damage one of the engine components between the piston and the crankshaft. |
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Post by steven on Jul 28, 2024 17:13:20 GMT 1
...the ones with the Athena head gaskets are the fastest, everyone knows that ! :-)
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Post by abar121 on Jul 28, 2024 20:44:36 GMT 1
...the ones with the Athena head gaskets are the fastest, everyone knows that ! :-) Always. FWIW, I didn't have to modify the head gasket on the last one at 1.5 over with an Athena. |
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Post by oldelsieboy on Jul 29, 2024 9:45:55 GMT 1
Hi guys,
Finishing up the engine rebuild on my '80 rd350lc, trouble I'm having is with setting my timing,
I'm trying to get the engine to TDC, but it always seems to spring/jump past TDC, I get to about 2.7mm before TDC and then the engine will jump forward past TDC by ~2.5mm's, it seems to do this no matter how fast or slow I turn the engine over, plugs are out and dial gauge is down the left spark plug hole,
This issue originally appeared as a hard spot before TDC where I can't turn the engine past it without either a breaker bar, or a fair bit of momentum with my 1/2" ratchet, this only appeared once the head was torqued down, I've taken the head on and off a few times now to confirm this, the squish is above 1.6mm as my solder was still intact when measuring so I don't think that the pistons are contacting the head either,
The jump feels like its compression related but this is my first engine rebuild so not really sure,
any got some ideas I could try?
What dial gauge are you using, does it have a selection of different length probes that screw into the end of the gauge? Maybe it's too long and not allowing the piston to reach TDC, when you apply additional force it bends slightly and springs past TDC giving a false reading 🤔 OEB  |
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Post by nakedgoose on Jul 29, 2024 21:11:36 GMT 1
Hi guys,
Finishing up the engine rebuild on my '80 rd350lc, trouble I'm having is with setting my timing,
I'm trying to get the engine to TDC, but it always seems to spring/jump past TDC, I get to about 2.7mm before TDC and then the engine will jump forward past TDC by ~2.5mm's, it seems to do this no matter how fast or slow I turn the engine over, plugs are out and dial gauge is down the left spark plug hole,
This issue originally appeared as a hard spot before TDC where I can't turn the engine past it without either a breaker bar, or a fair bit of momentum with my 1/2" ratchet, this only appeared once the head was torqued down, I've taken the head on and off a few times now to confirm this, the squish is above 1.6mm as my solder was still intact when measuring so I don't think that the pistons are contacting the head either,
The jump feels like its compression related but this is my first engine rebuild so not really sure,
any got some ideas I could try?
What dial gauge are you using, does it have a selection of different length probes that screw into the end of the gauge? Maybe it's too long and not allowing the piston to reach TDC, when you apply additional force it bends slightly and springs past TDC giving a false reading 🤔 OEB
Just an middle priced one from a local supplier, doesn't have adjustable lengths or anything like that,
the issue appeared before I even had the dial gauge, I just put it down to compression originally but now its most likely the head gasket in need of trimming,
Still haven't had a free moment to pull the head off and deal to it, I'll post again if it doesn't fix the issue but it seems like a known need for the OEM headgaskets and I just wasn't aware until this thread.
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Post by steven on Jul 29, 2024 21:25:02 GMT 1
.... if you have rotated the enginge with a breaker bar, and forced the piston over top dead centre, the piston has probably punched a hole in the gasket for you anyway. Why a breaker bar ? no buzz gun ? they seem to be all the rage these days.   Please let us know how it faired, once you get it stripped, thanks. Steven.  |
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Post by nakedgoose on Jul 30, 2024 3:50:09 GMT 1
.... if you have rotated the enginge with a breaker bar, and forced the piston over top dead centre, the piston has probably punched a hole in the gasket for you anyway. Why a breaker bar ? no buzz gun ? they seem to be all the rage these days. Please let us know how it faired, once you get it stripped, thanks. Steven. I dont have a rattle gun, maybe I should invest in one so the pistons resize the head gasket for me
In all seriousness its only a 10" bar and I wasn't really putting much strength into it, it probably wasn't the best idea but I've only worked on HI-comp 4 strokes so I thought that this head gasket issue was just compression XD
No damage that I can see, other than the coolant jackets starting to corrode a bit, but that was already another issue unrelated to my monkey brain,
The head gasket is obviously undersized, there is a pretty noticeable lip feeling up from the bore into the head gasket, I really should of caught that earlier but I guess you don't know what you don't know,
I've been grinding at the headgasket with the dremel and its slowly getting better although I'm not sure if I'll run the modified yam or go and buy an athena which seems like its already a larger bore, guess it'll be price dependent
seems like the head gasket is the issue, at this point I cant see how it isn't an issue so hopefully will have the room on my bench back soon,
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Post by nakedgoose on Jul 30, 2024 4:00:57 GMT 1
seems like the Athena are cheap enough, think I'll get one as it should get my squish closer to correct as well, just have to hope shipping isn't too bad
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Post by zig on Aug 4, 2024 21:37:01 GMT 1
could it be the wrong pistons fitted and the Skirt tab causing this  ZiG |
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