ande
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| posted on 15/7/15 at 02:49 PM |
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Engine advice needed
Hi, i have a 1300 crossflow from a mk1 fiesta, it has a large valve head on it, kent bcf3 cam with an adjustable sprocket and it has been bored out to
+40, i have another 1300 bored out to +60, i want to put the head, cam into the +60 block but someone said i will need to get the valve to piston
clearance checked so i don't get contact. Can you advise me on what i should do?
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snapper
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| posted on 15/7/15 at 02:59 PM |
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The difference between +40 and +60 is negligible in performance terms
Your better off sticking with what you have and getting it fully rolling roaded
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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ande
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| posted on 15/7/15 at 03:02 PM |
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so if i stick the parts back into the +40 would i still need to get the piston/valve clearance checked? or should it be the same as when i took it
out?
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Paul Turner
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| posted on 15/7/15 at 03:57 PM |
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quote:
Originally posted by ande
so if i stick the parts back into the +40 would i still need to get the piston/valve clearance checked? or should it be the same as when i took it
out?
If you re-build it exactly as it was before you dismantled it there should be no differences. But if you do not know what the cam timing was set at
previously you need to check clearances to be safe.
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ande
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| posted on 15/7/15 at 04:18 PM |
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will i have to do the valve clearances again or can i just put it back on?
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snapper
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| posted on 15/7/15 at 05:08 PM |
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You will need to do valve to piston checks once you have dummy built the engine
Use the old gasket bolted down and plasticine on the Pistons rotate engine by hand once cam timing has been set
Rocket gaps will need setting to specifications of the cam if it's not a standard cam
I eat to survive
I drink to forget
I breath to pi55 my ex wife off (and now my ex partner)
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ande
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| posted on 20/7/15 at 10:26 PM |
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on the +40 pistons the valve pockets are 4mm deep whereas the standard ford ones are 2.7, so i thought they must have had these machined to clear the
valves, i did a dummy build anyway with the plasticine and i had about 2mm between the piston and center of the valve, but on the radial i have 1mm if
that, so, is that too close?
apart from wanting to know if it is too close, i need advice on the following:
I have been told by some bloke on another forum that a kent bcf3 doesn't have any power at low revs anyway, to get it to work properly you need
higher than standard compression plus much modified 1.1 or 1.3 pistons.
I would be better off with my standard cam he said.
So what do i do? carry on with my +60 engine with standard parts, would it be worth my time putting the ported/polished head on it?
Is the bloke right in what he says or do i use the +40 with the cam etc by either having some more machined off the pistons or just risk the very
close p-v clearance?
Here is what i have, what do you think is my best combination, based on taking bits from either engine to make one i am going to use.
1300 with +60 pistons, otherwise standard.
1300 with +40 pistons, ported/polished head, kent bcf3 fast road cam and adjustable sprocket, full steel rocker assembly with rollers.
Carbwise, i have a brand new weber 32 dft twin choke as fitted to the 1300.
4 branch manifold and standard xr system.
Would really appreciate some advice, thanks.
ande
[Edited on 20/7/15 by ande]
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MikeRJ
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| posted on 21/7/15 at 11:17 AM |
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If the +40 bores and bottom end are in good condition then I'd go with that. The BCF3 is a fairly warm cam, you will lose some low end torque
and the idle may be slightly rough but you will gain a significant amount of mid-high end power over the standard camshaft. That said, it's
nowhere near a "race" or "rally" profile, so should be be perfectly usable on a road car.
The BCF3 is supposed to be able to be used without piston mods, but the clearance is marginal. On an otherwise standard engine, a few degrees of
timing or a slightly thinner headgasket could cause valve/piston contact so the clearance should always be checked. Even though your piston cut outs
have been increased in depth, you don't know what else has been done so I would still measure them.
Valve clearances on an OHC engine have to be reset every time the head comes off, but this is a very simple job.
[Edited on 21/7/15 by MikeRJ]
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ande
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| posted on 21/7/15 at 11:36 AM |
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Hi, thanks for your reply, the bores are in excellent condition, i don't think this engine has seen the road since being built or if it has then
not very much, the engine has sat in an incomplete kit car for some years, is there any specific reason you would go with the +40? both the +40 and
+60 are fairly fresh, infact the +60 hasn't even been started yet. The piston to valve clearance is very close on the +40 but i don't
know enough about them to set it properly, a slight adjustment on the cam might be all it needs, you say the bcf3 is designed to need no piston mods?
if i were to put the cam in with the standard ford sprocket, would that increase the gap?
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Paul Turner
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| posted on 21/7/15 at 11:36 AM |
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quote:
Originally posted by MikeRJ
Valve clearances on an OHC engine have to be reset every time the head comes off, but this is a very simple job.
[Edited on 21/7/15 by MikeRJ]
But the OP is fitting (refitting) a x-flow which is OHV.
But whatever the engine the valve clearances should be checked before use.
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ande
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| posted on 21/7/15 at 11:43 AM |
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would i be right in thinking that if a bcf3 is designed to fit without piston mods, then swapping the adjustable sprocket with the standard ford one
should clear the pistons, which are slightly deeper than standard so even more so.
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MikeRJ
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| posted on 24/7/15 at 01:42 PM |
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quote:
Originally posted by Paul Turner
quote:
Originally posted by MikeRJ
Valve clearances on an OHC engine have to be reset every time the head comes off, but this is a very simple job.
[Edited on 21/7/15 by MikeRJ]
But the OP is fitting (refitting) a x-flow which is OHV.
But whatever the engine the valve clearances should be checked before use.
Well spotted, I meant to write OHV  Clearances on an OHC engine don't change when the head is removed.
quote:
Originally posted by ande
would i be right in thinking that if a bcf3 is designed to fit without piston mods, then swapping the adjustable sprocket with the standard ford one
should clear the pistons, which are slightly deeper than standard so even more so.
The whole point of a vernier sprocket or offset drive pegs is to time in the cam to get the best power. Even if you just want to set the cam
manufactures standard timing (which is often not optimal anyway) you will still need some method of adjusting the timing since most after-market cams
are not particularly accurately ground with respect to the key way.
By fitting the standard crossflow sprocket and throwing everything together without setting the cam timing properly you could easily be throwing away
a significant amount of power and/or torque.
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ande
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| posted on 24/7/15 at 09:56 PM |
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i went to an engine specialist today and told him i had like 1mm piston to valve clearance and he said just run it, it will be fine, i wasn't
convinced though, thought i would check the valve clearances and see if it would give me a bit more, looked at the specs for this cam and it says
.016" inlet and .016" exh, so i checked them and they seemed way too tight, so i loosened them off to .016", did another dummy build
and still too close, infact, maybe even closer! how could that happen, surely loosening the rockers off would result in less push on the valves
wouldn't it?
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