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Small block home tune

Need help with a tuning kit, how do you tune your scooter, which kit should I choose, and all general tuning and modifcations questions are for in here.

Re: Small block home tune

Postby dickie » Sun Jul 14, 2019 7:22 pm

so, I fitted this engine into my LI series 3 bitsa, did a couple of short local rides, 1 mile, 5 mile, 10 miles. Then, i rode it the fairly short journey of about 20 miles to the WWSC rally in sunderland. It really is lovely to ride: easy starter, flexible and pretty nippy.

BUT, on the way home this morning, it very suddenly cut out. It felt ignitiony, but wasn't.

Image20190714_183154 by richardhenderson1968, on Flickr

Image20190714_183418 by richardhenderson1968, on Flickr

Image20190714_183304 by richardhenderson1968, on Flickr

Image20190714_183406 by richardhenderson1968, on Flickr

the failure mode is obvious, what isn't so obvious to me is the reason for it. piston bore clearance was 4 thou. ring gap was good. But I've obviously done something wrong, but what?
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Re: Small block home tune

Postby ULC Soulagent » Sun Jul 14, 2019 7:40 pm

Air leak
Lack of oil
Or pushing it too hard while still running in :cry:
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Re: Small block home tune

Postby MickYork » Sun Jul 14, 2019 7:44 pm

foreign object entering barrel ?

A leak test before you stripped it down would have been useful....
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Re: Small block home tune

Postby dickie » Sun Jul 14, 2019 8:04 pm

MickYork wrote:foreign object entering barrel ?

A leak test before you stripped it down would have been useful....


Bugger. You're right, I should have done. I don't think it was leaking though as I leak checked it during the build and all was good. Also, here's the plug which indicates it wasn't leaking.

Image20190714_181200 by richardhenderson1968, on Flickr

What makes you suggest foreign object? Wouldn't there be some witness marks on the head or piston crown?

Image20190714_182756 by richardhenderson1968, on Flickr

Image20190714_182811 by richardhenderson1968, on Flickr
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Re: Small block home tune

Postby dickie » Sun Jul 14, 2019 8:08 pm

ULC Soulagent wrote:Air leak
Lack of oil
Or pushing it too hard while still running in :cry:


My money is on number 3, but what happened? I run 3% as i always have done on all my scooters. I don't think air leak; see my other answer to Mickyork.

I must admit, I think I hit about 55mph. :oops: It's done less than 100 miles. Probably less than 50.
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Re: Small block home tune

Postby MickYork » Sun Jul 14, 2019 8:21 pm

Looking at the plug i agree an air leak looks unlikely.

Just a thought with the foreign object...it does happen and can cause the damage then disappear out of the exhaust.
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Re: Small block home tune

Postby coaster » Mon Jul 15, 2019 9:30 am

Its not too clear in the top photo but could your rings have been snagging on the bottom of the exhaust port? I had that problem on a tuned barrel once and the snagging caused the rings to stick in their groves and loose compression, the damage looked very similar to yours :?
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Re: Small block home tune

Postby Nudger » Mon Jul 15, 2019 10:19 am

dickie wrote:I must admit, I think I hit about 55mph. :oops: It's done less than 100 miles. Probably less than 50.

This is where I'd put my money
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Re: Small block home tune

Postby Rich Oswald » Mon Jul 15, 2019 10:24 am

Nudger wrote:
dickie wrote:I must admit, I think I hit about 55mph. :oops: It's done less than 100 miles. Probably less than 50.

This is where I'd put my money


+1
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Re: Small block home tune

Postby Warkton Tornado No.1 » Mon Jul 15, 2019 12:20 pm

Looking @ the piston, I get mixed messages (probably because of my eyesight!) but it almost looks as though the piston was fitted upside down as there 'appears' to be pegs & ring ends......

As I said, my eyesight, most probably.

That said, the seizure & consequent meltdown was probably due to a soft sieze earlier (that you may have been unaware of) causing ring(s) to stick in the groove which, unless rectified, causes a massive heat build up in the extremely rough area of the piston & bore, leading to the resultant catastrophic sieze.

The other conditions such as burn colour & prior bore condition all look good. The exhaust port could probably have benefitted from being a softer shape, but as the sieze marks & it aren't precisely in line, I doubt it is too wide.

If I were you, I would check the crankshaft, then clean up the bore & even the piston if it is not too bad, & check the resultant clearance. You may get away with new rings. That said, if a fresh piston is required, I would advise that a thin, chrome, two ring piston be sought.

If you do hone it yourself, a really slow drill is required to achieve the correct cross hatch. For that alone, it is worth having the Milwaukee 18v combi drill because the control & torque is ideal.
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Re: Small block home tune

Postby dickie » Mon Jul 15, 2019 12:39 pm

Thanks gents. There may be a few factors here. I've since nosed around a bit more and found a leak at the plug. The sealing face for the plug is knackered; I'm not sure if this is something I missed during the build or happened after, but it leak checked really good. I can't upload photos from work so I'll do it when I get home.

Anyway, I'm going to replace head and piston. I may also gut the pipe and add a tailpipe silencer on Darrell Taylor's advice as he suggests it has 'gassed up'. The pipe has been repaired internally after baffle failure, so may have become more restrictive than a regular bgm?
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Re: Small block home tune

Postby Adam_Winstone » Mon Jul 15, 2019 12:59 pm

Rich Oswald wrote:
Nudger wrote:
dickie wrote:I must admit, I think I hit about 55mph. :oops: It's done less than 100 miles. Probably less than 50.

This is where I'd put my money


+1


+2 ... running in is about more than just clearance. As the book suggests, you don't seem to have done no more than 34mph for the first 900 miles!
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Re: Small block home tune

Postby dickie » Mon Jul 15, 2019 6:09 pm

Warkton Tornado No.1 wrote:Looking @ the piston, I get mixed messages (probably because of my eyesight!) but it almost looks as though the piston was fitted upside down as there 'appears' to be pegs & ring ends......

As I said, my eyesight, most probably.

That said, the seizure & consequent meltdown was probably due to a soft sieze earlier (that you may have been unaware of) causing ring(s) to stick in the groove which, unless rectified, causes a massive heat build up in the extremely rough area of the piston & bore, leading to the resultant catastrophic sieze.

The other conditions such as burn colour & prior bore condition all look good. The exhaust port could probably have benefitted from being a softer shape, but as the sieze marks & it aren't precisely in line, I doubt it is too wide.

If I were you, I would check the crankshaft, then clean up the bore & even the piston if it is not too bad, & check the resultant clearance. You may get away with new rings. That said, if a fresh piston is required, I would advise that a thin, chrome, two ring piston be sought.

If you do hone it yourself, a really slow drill is required to achieve the correct cross hatch. For that alone, it is worth having the Milwaukee 18v combi drill because the control & torque is ideal.


thanks Mark, if there was a soft seize, I'm too insensitive to notice, although my wife says I have a wonderful touch. Even when it failed completely, it did not seize, it just suddenly stopped producing power, just as if the HT lead had come off.

I tried to get the rings out, but without doing significant damage to the grooves, it's toast, so it's a new one for £60 :roll:

Which piston would you recommend over an Asso 2 x 1.5m ring?

The friend who recovered me from the side of the road has a honing tool and assures me he knows what he's doing. He is a good engineer, so I'll trust it to him.
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Re: Small block home tune

Postby dickie » Mon Jul 15, 2019 6:24 pm

I didn't nurse my new engine the way I should have done, and I may have a heat build up issue with the exhaust, but I'm fairly convinced that a leak at the plug is the main cause of excess heat. Even if it isn't, it needs to be corrected.

If this damage was apparent when I built it, I either chose to ignore it or didn't notice it for some reason. I guess the oily deposits around it make it more obvious.

Image20190715_170841 by richardhenderson1968, on Flickr

Image20190715_170841 by richardhenderson1968, on Flickr

I'd estimate that it's about 1mm deep, so the threads are doing the sealing rather than the face and crush washer. There's obviously a leak as you can see the deposits inside the cowl; bear in mind this motor has only done about 50 miles or so, so that's a lot of oil for such a short distance.

Imagehttps://flic.kr/p/2gyAE2e by richardhenderson1968, on Flickr

I'd like to have the head repaired as it has been machined to get correct squish with no gasket and has the the corrected compression ratio I want. As well as being dowelled for my barrel. of course I can do all this again, but I'd rather not.

What can I do to get this sorted? And does the plug protrude too far into the bowl? I don't have another head to compare it with.

Image20190715_174938 by richardhenderson1968, on Flickr
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Re: Small block home tune

Postby dscscotty » Mon Jul 15, 2019 9:03 pm

Although its evident the heads been leaking my view would be that its not major issue relating to the seizure, if it were there would be evidence on the piston crown/head, cratering, greyish covering and evidence of a lean mixture, however the head/plug/etc suggests this was not the case, infact it looks like its been pretty spot on . You'd be surprised at how many cylinder heads including new so called high spec ones around the spark plug thread, leakdown testing/pressure testing often reveals leaks, but sometimes they dont.
My view would be that this seizure has occurred due to the exhaust possibly gassing up and creating excessive heat around the exhaust port/underside of the piston, I've seen this several times on motors fitted with clubmans, where the issue was resolved by either a change in pipe or the tailpipe/box pipe has been modified.
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Re: Small block home tune

Postby Knowledge » Mon Jul 15, 2019 10:20 pm

Dickie,

I have the tools to re-machine the plug seat. I’ll send you a pm.

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Re: Small block home tune

Postby Warkton Tornado No.1 » Tue Jul 16, 2019 12:58 am

dickie wrote:
Warkton Tornado No.1 wrote:Looking @ the piston, I get mixed messages (probably because of my eyesight!) but it almost looks as though the piston was fitted upside down as there 'appears' to be pegs & ring ends......

As I said, my eyesight, most probably.

That said, the seizure & consequent meltdown was probably due to a soft sieze earlier (that you may have been unaware of) causing ring(s) to stick in the groove which, unless rectified, causes a massive heat build up in the extremely rough area of the piston & bore, leading to the resultant catastrophic sieze.

The other conditions such as burn colour & prior bore condition all look good. The exhaust port could probably have benefitted from being a softer shape, but as the sieze marks & it aren't precisely in line, I doubt it is too wide.

If I were you, I would check the crankshaft, then clean up the bore & even the piston if it is not too bad, & check the resultant clearance. You may get away with new rings. That said, if a fresh piston is required, I would advise that a thin, chrome, two ring piston be sought.

If you do hone it yourself, a really slow drill is required to achieve the correct cross hatch. For that alone, it is worth having the Milwaukee 18v combi drill because the control & torque is ideal.


thanks Mark, if there was a soft seize, I'm too insensitive to notice, although my wife says I have a wonderful touch. Even when it failed completely, it did not seize, it just suddenly stopped producing power, just as if the HT lead had come off.

I tried to get the rings out, but without doing significant damage to the grooves, it's toast, so it's a new one for £60 :roll:

Which piston would you recommend over an Asso 2 x 1.5m ring?

The friend who recovered me from the side of the road has a honing tool and assures me he knows what he's doing. He is a good engineer, so I'll trust it to him.


Unfortunately, Scooter Restoration's own pistons (1.0mm rings) are not available to suit 62.0 mm, though if your bore started out @ four thou' clearance, you might find that you need a rebore. In which case, they had 62.5 mm kits available. The Indian 175 alloy barrel kits are appallingly made & take many hours to fettle, but the pistons with them are amazingly robust. I would aim for a 'tight' three thou' (though any excess clearance was not instrumental in your problem)

I had forgotten your choice of exhaust & reading other comments, it does appear your exhaust had insufficient bleed to cause the back-up. IMHO, on a 200, there needs to be one inch minimum bore tailpipe, so pro-rata a 175, I'd be looking toward 7/8" (22.2 mm) minimum bore.
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Re: Small block home tune

Postby dickie » Tue Jul 16, 2019 5:24 am

Has anyone tried one of these? Pennies and I could get my head good as new (ish).

https://rover.ebay.com/rover/0/0/0?mpre=https%3A%2F%2Fwww.ebay.co.uk%2Fulk%2Fitm%2F221720834470

I'll look into those SR pistons, but there doesn't appear to be any significant bore damage after I've cleaned it up with wet and dry unless my cleaning has ovalled the bore slightly?
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Re: Small block home tune

Postby Warkton Tornado No.1 » Tue Jul 16, 2019 9:51 am

I have used them, though the kit I used was genuine Helicoil, even though they are not wire inserts. Currently, my SX has one & there has only been one issue to watch out for. Another was fitted to a Group Four head & that was fine.

There can be a little leakage around the outside of the insert, which is overcome by selecting the 'better' captive washers (from old spark plugs if needs be) & using them to ensure a good seal. The alternative of solid copper washers also works, but I prefer a captive washer with a conventionally positioned plug, as it is too easy to lose them in the depths of the cowling :roll:

It's something I just have to be aware of, & would not be an issue had the insert been fitted with a Loctite type sealant.
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Re: Small block home tune

Postby sunrisemac » Wed Jul 17, 2019 11:10 pm

Having had a look at your photos I think there may be a couple of points worth considering.

Although the burn colour on the head and piston crown look good, there is no squish band area on the head which seems to align with the position on the piston on the inlet side that appears to have had the seize. At the point of ignition, and just after, when the flame front is at its peak there is nothing to shield and slow the hot gases from flowing down the side of the piston towards the rings, (see the brown colouring at the top of the bore), and overheating that area of the piston which may possibly be causing problems with lubrication and clearances.

When running in IMHO it can be more detrimental to over oil the fuel mix, run at low revs and make the engine labour without much cooling being produced by the fan. Periodically give it a good few revs for a short burst then let it cool down so to get the new surfaces through a series of heat cycles to bed it all in.
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