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Offline barry.t100sr

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Re: 12,000 mile service...do the valves really need checking?
« Reply #60 on: November 19, 2020, 06:01:43 PM »

I'm prepared to be shot down on this idea, but here goes anyway  :002:

My understanding is that valve clearances on Triumph engines usually tighten up over time due to valve seat recession, and they are also tighter when the engine is cold.  This can result in difficult cold starting but  the engine will run ok when warmed up, until the clearance reduces to zero even when hot.

So, instead of pulling the engine apart to check clearances, why can we not rely on a simple compression test to indicate if there is clearance ?
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Offline Paulhere

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Re: 12,000 mile service...do the valves really need checking?
« Reply #61 on: November 19, 2020, 06:26:05 PM »
No!  :192:
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Offline barry.t100sr

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Re: 12,000 mile service...do the valves really need checking?
« Reply #62 on: November 19, 2020, 06:38:39 PM »
*Originally Posted by Paulhere [+]
No!  :192:

Thanks for your quick response Paul, but my question was "why".
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Offline Paulhere

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Re: 12,000 mile service...do the valves really need checking?
« Reply #63 on: November 19, 2020, 06:46:17 PM »
*Originally Posted by barry.t100sr [+]
Thanks for your quick response Paul, but my question was "why".

Your min exhaust being 0.325mm, if it was 0.025 (1 thou) it would be shut & compression ok, a few miles down the road it'd be open, burning your valve & seat. A mechanic told me he did it your method to save time, glad he told me, I wouldn't let him on my bike.
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Offline awjdthumper

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Re: 12,000 mile service...do the valves really need checking?
« Reply #64 on: November 19, 2020, 07:17:15 PM »
*Originally Posted by barry.t100sr [+]
Thanks for your quick response Paul, but my question was "why".
The valve clearances are not there simply to avoid zero clearance when the engine is hot but to allow the cams to open and close the valves quietly. If you let the clearances close up too much, the top end of the engine is likely to start to rattle!



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Offline barry.t100sr

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Re: 12,000 mile service...do the valves really need checking?
« Reply #65 on: November 19, 2020, 07:31:28 PM »
*Originally Posted by awjdthumper [+]
The valve clearances are not there simply to avoid zero clearance when the engine is hot but to allow the cams to open and close the valves quietly. If you let the clearances close up too much, the top end of the engine is likely to start to rattle!

Surely it's the other way round ?
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Offline street tango

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Re: 12,000 mile service...do the valves really need checking?
« Reply #66 on: November 19, 2020, 08:42:25 PM »
*Originally Posted by barry.t100sr [+]
Surely it's the other way round ?
Correct.

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Re: 12,000 mile service...do the valves really need checking?
« Reply #67 on: November 19, 2020, 09:20:00 PM »
*Originally Posted by barry.t100sr [+]
Surely it's the other way round ?

Yes. It is better to have valve clearances too big/loose rather than too tight which risks burnt valves as seats .... hence, in my day, mechs were taught 'a noisy tappet is a happy tappet'.  :028:
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Offline JohnTz

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Re: 12,000 mile service...do the valves really need checking?
« Reply #68 on: November 20, 2020, 04:59:10 PM »
By the time you see any measurable compression issue the damage is done.

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Re: 12,000 mile service...do the valves really need checking?
« Reply #69 on: November 20, 2020, 05:57:17 PM »
*Originally Posted by barry.t100sr [+]
My understanding is that valve clearances on Triumph engines usually tighten up over time due to valve seat recession, ....

On old Meriden Triumphs designed to run on leaded petrol possibly, but modern engines, like Hinkley Triumph, designed for unleaded I don't believe they suffer valve seat recession. In fact after LRP was phased out well before expectation I have had no option but to run my 79 Bonnie on unleaded fuel and I've not suffered any valve seat recession to date. At the start I kept an extra regular check on valve clearances as the obvious way to spot any issue and have never found any accelerated clearance closing.  :028:
Also owned my 1979 Bonnie T140E from new!

We don't stop playing because we grow old .. WE GROW OLD BECAUSE WE STOP PLAYING!!!


 


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