No sniggering at the back, please... It's the cold weather... Honest!
Stripping my engine, one of the bushes in the connecting rod is loose. ie it revolves and pushes in and out. If I buy new bushes will this help or is the connecting rod junk?
Thanks,
Mike.
Small end
Re: Small end
You really need to measure the rod eye inside diameter to know for sure. Check size, ovality and even taper.
Excess clearance between the bush and gudeon pin can lead to the bush being hammered out and coming loose. It can also lead to the rod eye ending up oval. The same thing can happen to the big end of the rod. On plain split rods, the cap and rod can be skimmed and the big end bore honed back into round. The serrated joint used by Morini, means that this isn't an economical fix.
Excess clearance between the bush and gudeon pin can lead to the bush being hammered out and coming loose. It can also lead to the rod eye ending up oval. The same thing can happen to the big end of the rod. On plain split rods, the cap and rod can be skimmed and the big end bore honed back into round. The serrated joint used by Morini, means that this isn't an economical fix.
Paul Compton
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
http://www.morini-mania.co.uk
http://www.youtube.com/user/EVguru
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MickeyMoto
- Posts: 2420
- Joined: 22 Nov 2008 17:41
- Location: Even further oop North
Re: Small end
Thank you. I'll have a measure up.
Mike.
Mike.
Re: Small end
The small end on my Gilera 98 was toast. Not just worn but cracked. When lifted the cylinder the piston was wobbling from side to side like a 'nodding dog'.
Not listed as a separate part and though pattern rods are available they are £100 and would mean a total engine strip.
I didn't intend to keep it long, so not worth the hassle. In the end I got a local CNC place to machine me up a new bush to the dimensions given in the manual (actually for the earlier small 13mm diameter pin because I found a better used piston of that type). They allowed a bit extra on the nominal OD to make it tight fit but it was still a bit easy to start pulling in with a bolt, tube and spacers than I'd like, so I used some spiffy high temp Loctite bearing retainer gloop for final assembly cured with hot air.
Before pulling it in properly though, I had to drill two oil feed holes. Unlike a Morini with a sensible single one on the top of the rod small end eye this had two from the underside of the eye. Impossible to do in situ. So I marked up the new bush and drilled it as accurately as I could with my drill stand and Black & Decker. Then using a jewellers loupe and very strong light I pulled it in to place with a smear of the Loctite. Amazingly I kept it in line as confirmed by poking with a tiny allen key.
Naturally after pulling in, the bush was compressed enough that the pin wouldn't go through. If it's worth bodging, it's worth really bodging, so I used an adjustable reamer very carefully until the pin would just about push through with a bit of pressure. Should have been honed of course and every chance of not being parallel, but by then I was in 'shit or bust' mode.
Amazingly, on offering up a hot piston (the ever useful hot air gun again), the pin went home quite easily and the piston pivoted nicely. So I put the top end back on and it started up easily and was noticeably mechanically quieter. I did nearly 100 miles on it without anything nasty happening. Then I sold it, but in the Ebay description explained that it had a DIY custom small end bush and that I reckoned the engine needed a complete rebuild anyway. The big end had no up and down play but excessive side play. Plus the gear change return spring was broken and on the Giubileos of that era (1970) it's a crankcase split to change it.
Anyway, on a Morini the small end has got a part number and so clearly is meant to be changed. Shouldn't be too hard with the rods out. Though you might possibly be looking at honing afterwards I suppose? On my Morini hill climb engine rebuild the big end eyes had gone oval, but the small end bushes weren't loose in the rods at least. The last two new rods on NLM's shelf sorted it all anyway
Not listed as a separate part and though pattern rods are available they are £100 and would mean a total engine strip.
I didn't intend to keep it long, so not worth the hassle. In the end I got a local CNC place to machine me up a new bush to the dimensions given in the manual (actually for the earlier small 13mm diameter pin because I found a better used piston of that type). They allowed a bit extra on the nominal OD to make it tight fit but it was still a bit easy to start pulling in with a bolt, tube and spacers than I'd like, so I used some spiffy high temp Loctite bearing retainer gloop for final assembly cured with hot air.
Before pulling it in properly though, I had to drill two oil feed holes. Unlike a Morini with a sensible single one on the top of the rod small end eye this had two from the underside of the eye. Impossible to do in situ. So I marked up the new bush and drilled it as accurately as I could with my drill stand and Black & Decker. Then using a jewellers loupe and very strong light I pulled it in to place with a smear of the Loctite. Amazingly I kept it in line as confirmed by poking with a tiny allen key.
Naturally after pulling in, the bush was compressed enough that the pin wouldn't go through. If it's worth bodging, it's worth really bodging, so I used an adjustable reamer very carefully until the pin would just about push through with a bit of pressure. Should have been honed of course and every chance of not being parallel, but by then I was in 'shit or bust' mode.
Amazingly, on offering up a hot piston (the ever useful hot air gun again), the pin went home quite easily and the piston pivoted nicely. So I put the top end back on and it started up easily and was noticeably mechanically quieter. I did nearly 100 miles on it without anything nasty happening. Then I sold it, but in the Ebay description explained that it had a DIY custom small end bush and that I reckoned the engine needed a complete rebuild anyway. The big end had no up and down play but excessive side play. Plus the gear change return spring was broken and on the Giubileos of that era (1970) it's a crankcase split to change it.
Anyway, on a Morini the small end has got a part number and so clearly is meant to be changed. Shouldn't be too hard with the rods out. Though you might possibly be looking at honing afterwards I suppose? On my Morini hill climb engine rebuild the big end eyes had gone oval, but the small end bushes weren't loose in the rods at least. The last two new rods on NLM's shelf sorted it all anyway
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harrymuffin
- Posts: 292
- Joined: 07 Apr 2014 16:06
- Location: west midlands
Re: Small end
You should use a reamer after fitting the little ends, not hone, it will leave a traces of fine grit in the bearing material. I think the little end bushes, without going across to the garage to look at half a dozen sitting on the window ledge are Glacier type split bushes. I did actually once buy some from NLM and they did not fit, so I made my own.
Re: Small end
Well I certainly knew that 'lapping' with a bit of wet and dry was a no-no. I found reference to using a "Sunnen Hone" for bushes when researching before doing the 98 . A cheap adjustable reamer off Ebay seemed like more in keeping with the cost-cutting approach though. Tricky adjusting it in tiny increments as it neared a good fit for the pin though and nerve wracking keeping it parallel without some kind of guide and working with the engine still in the bike.harrymuffin wrote:You should use a reamer after fitting the little ends, not hone, it will leave a traces of fine grit in the bearing material. I think the little end bushes, without going across to the garage to look at half a dozen sitting on the window ledge are Glacier type split bushes. I did actually once buy some from NLM and they did not fit, so I made my own.
The bushes in the fubar rods from the project rebuild look as if they are split type and also with an X shaped oil groove centred on the hole in the small end.