New lifters don't fit

My latest issue with my engine rebuild is that the new tappets I bought from Norvil won't quite slide into the cyliner bores (850 Commando). Individually they fit into the holes, but with two together they get stuck. It seems as though the combined width of two together is a couple tenths too big.

I could probably tap them down with a mallet, but that just feels wrong. I don't want them to hang when the engine is running. Why do brand new parts not fit? Are they supposed to be tight, or is something wrong?

The package they came in says to remove any machining burrs and I've done that.

<sigh> Maybe someday I'll get this old girl together.

I sure wouldn't tap them in Dave. My opinion would be to contact Norvill, but I'd probably end up trimming them down if they are the correct part. It seems to me that pattern parts in the bike world (I have a few brands) have to be hand fitted these days. Honest, I recall buying parts from the dealer that actually fit in the early 70s.

Maylar

Time to break out the micrometer to check dimensions against the factory specs. The lifters may just need the flat sides dressed down a few thou to make them work, unless of course you got the oversize replacements by mistake.

Take heart, the more time and effort you put into the rebuild the more you will appreciate the old girl once she's done.

Scooter

I too, recently experienced the same with new lifters. I lapped the flat sides. A few trips over some 400 grit sandpaper on a glass plate fixed that. I then polished them. I would measure the bore and lifter diameters before I started lapping. As previously stated, you could have oversize lifters. Under no circumstance should they be forced into the bore.

I bought two sets, which come as "matched" pairs. Matched to what, I wonder? Both sets are a very tight fit in the bores. The factory manual doesn't specify the diameter, and my bore gage doesn't read tenths of thousandths so it'll be an "eyeball" measurement at best. I expected them to just drop in but noOOOooo.

One guy on the BI mail list says they're oversized on purpose and you're supposed to grind them in with fine lapping compound. WTF?

I'm gonna take a Dremmel to the suckers. Grrrr.

The fact that they are slightly tight gives the option of honing the guide bores, or fettling the new followers to ensure the correct fit, this is much better than having them sloppy and making a noise. I wouldn't use a dremel on them, just some patient engineering work.

No way they are "a couple of tenths" off!

JimC has it exactly right as to the fix.

maylar said:

I'm gonna take a Dremmel to the suckers. Grrrr.

Click to expand...

Imagine the frustration if they were undersized... I'd much rather have them too big.

Hello,

I just fitted my new genuine Norton matched lifters. The note on the bag said they purposely do not de-burr. I de-burred and they were still tight. I used 600 then 1200 paper on them until they were a perfect sliding fit. Took about an hour for the whole installation. I am glad they were not too loose out of the factory,

Jerry

maylar said:

My latest issue with my engine rebuild is that the new tappets I bought from Norvil won't quite slide into the cyliner bores (850 Commando). Individually they fit into the holes, but with two together they get stuck. It seems as though the combined width of two together is a couple tenths too big.

I could probably tap them down with a mallet, but that just feels wrong. I don't want them to hang when the engine is running. Why do brand new parts not fit? Are they supposed to be tight, or is something wrong?

The package they came in says to remove any machining burrs and I've done that.

<sigh> Maybe someday I'll get this old girl together.

Click to expand...

While you have everything apart, check to make sure the pushrod tunnels are nice and clean. When I disassembled mine, there was a lot of grimy crud in there including what looked like sand from the casting process!! The sides of one pair of tappets were scored up pretty well which I assume was from this sandy crud. I am pretty sure this engine had never been apart so the only explanation I have is that this sandy crud has been in my pushrod tunnels since the bike left the factory!! So make sure you get the tunnels squeaky clean, otherwise you risk damage to your new lifters.

I second the other opinions on here about making sure the lifters fit perfectly and using proper machine tools to achieve a good fit. Take them to a good machinist and make sure they are a perfect sliding fit. Very rarely are parts a drop-in fit for me. I am sure most of the Commandos that need new lifters have slightly oversize tappet bores which might explain why yours are tight. I guess you could consider yourself lucky that your engine does not appear to have a high level of wear!!

hi maylar,i dont think you need a machineist unless you,ve got the oversize cam followers,a couple hours with fine wet and dry paper and a bit of elbow grease is all you need,after a few trys you will identify the high spots,one thing i found was tightening the 4 small screws too tight it tended to nip the followers,so dont over tighten them , with lock wire they wont come out, aim for a finger slideing fit and they should fall back down under there own weight,that goes for the locating plates too. in your query about matched pairs i think they are matched to each other not anything else,try mixing them up and see what fits best , you could always grind the chamfer on the other side of the follower

I've always found it necessary to lap new followers in and it does mean a nice rattle-free fit. Usually a quick figure-of-eight on a new oilstone followed by fine grinding paste and an old pushrod in the tunnels. It is essential that the new followers, when everything is thoroughly cleaned and lightly oiled, can fall under their own weight and be lifted with light finger pressure.

The oil drain chamfer on the leading edge of the follower pairs can vary between sets - check to make sure that the unworn area there is not the cause of the problem.

The NOC 'Service Notes' make reference to casting sand in OE sand cast followers. It was one of John Hudson's recurring themes. I think that he'd seen quite a lot of it. This is something that would not now be found in the current lost-wax cast followers