Hi all, I ran a compression test this evening, as part & parcel of trying to diagnose Harvey's latest little upset. I got the following numbers: 125 psi 110 psi 105 psi 82 psi - rising to 92 with a little oil down the plug-hole. I'm not sure about 2 & 3...the compression tester may not have been fully screwed in. They were a little fiddly, but 4 is clearly down. I'm interpreting the change from 82 to 92 psi as indicative that part of the low pressure is due to worn piston rings, but there may also be valve guide wear too, since the pressure didn't get up above 100 psi, like the other barrels. I guess a top end rebuild would be a good idea - I have an (almost) unused set of 1641 Bs & Ps, and a pair of heads available, but I'd prefer to hold off until the winter. Should I be overly concerned by that low number on 4, or will it be OK for a few months? By 'overly concerned', I guess I mean...could it be 1) contributing significantly to the general running issues that have been keeping me entertained since getting Harvey or 2) likely to deteriorate into something more serious/expensive than a top end rebuild? cheers P.
Not the best idea , Ever twist your foot . . I have . When walking for a few days . My back seems to hurt next. Same principle 95 o.k. But below ? 82 ! You answered your own question, Shirt trips only. Ok . But warm it up! So the ring/expands .
Did you set your valves first? All plugs out? Foot flat on the go pedal? No.2 is the easiest to get at??
Although the numbers should be within 10% of each other I don't think you'd notice the low one too much. I'd go for a full rebuild rather than just the top end if and when...
Fair enough...2 and 3 were just a bit stiff to screw in, compared to the others. I'm pretty sure they were screwed fully home...but not 100%. Yup...recently set the valves. Ran the tests with the other plugs in...will re run and see what happens.. P.
You might find the readings went down as you went round because the engine wasn't spinning quite as fast by the time you finished, so any leaks are more exagerated. Taking out the plugs and putting you foot down make it easier to turn the engine and lessen the effect. Try starting on 4 and going the other way round next time?
So taking Zed's advise I've just retested with all plugs out (and ofc no manifolds)...the figures are a little better: 148 psi 136 psi 148 psi 115 psi (and 139 psi with a little oil down the bore) I interpret that as the heads are fine (or at least all equally worn) but the rings on #3 need replacing. I'll schedule a rebuild for the next few months. A have a spare T1 (i.e. not is universal case), which needs a rebuild anyway...would it be feasible to drill & tap this to accept bolts for the rear support...I think the bosses are there, just not drilled & trapped...? P.
Fair point, @zed. Though I've noticed that the stock air filter is splattered with oil from the breather pipe, that links from the filler neck. I guess this isn't standard behavoiur? I had assumed that this we as caused by over pressure in the case, caused by some degree of blow by( from what now would appear to be #4). We'll see when I strip it all down. Quite looking forward to it. P.
